Effect of some selected tree species on soil attributes and yield of millet (pennisetum typhoides) under semi arid environment. By Mohammed Hussein Abdalla B.Sc. Forestry Science Faculty of Forestry and Range Science Sudan University For Science And Technology 1999. Supervisor Dr. Mubarak Abdelrahman Abdalla A thesis Submitted to the University of Khartoum in partial Fulfillment of the Requirements for the degree of M.Sc of Science in Desertification Desertification and Desert Cultivation Studies Institute, University of Khartoum June - 2008. Dedication To my father To my mother To my wife To my son Eihab To my brothers and sisters To my friends and my colleaques With love and respect Mohammed i Acknowledgments My gratitude and appreciation to Allah who provides me with health and strength. I would like to express my sincere gratitude to my supervisor Dr. Mubarak Abdelrahman Abdalla for his valuable advice and directions throughout the study. Special thanks to the director of Eldubibat Forestry Mr. Gumaa Mukki for his assistance and cooperation during study. Grate full thanks for my family for their patience. Deepest gratitude and appreciation are also extended to the director of the Forestry of South Kurdofan State. My gratitude is extended to the director of Lugawa Forestry Mr. Mohammed Osman. My thanks also extended to the staff of (DADACSI) for advices and encouragement. Full thanks are extended to my dear colleaques in Institute for their assistance during laboratory analysis and so my friends. Also thanks are extended to any person who supported the processing study. ii Abstract Trees tend to improve soil fertility by changing the chemical properties, physical structure, microclimate, infiltration capacity and moisture regime of the soil. Two field experiments were carried out in south Kordofan State (between July and November (2006),) to determine (in the first experiment) the contribution of three selected trees (Acacia senegal, Blanites aegyptiaca and Azadirachtica indica) to millet (Pennisetum typhoides) and soil quality and to monitor (in the second experiment) decomposition and nutrients release of the litters from these tree species. The results showed that millet yield under the Neem (174.83 kg/ha) and Heiglig (173.09 kg/ha) were significantly (P≤0.03) higher than the control (121.43 kg/ha) by an average of 43%. The lowest yield (111.04 kg/ha) was recorded under the Hashab trees. Similarly, straw dry matter in the Heiglig (1161.5 kg/ha) and Neem (857.8 kg/ha) were significantly (P ≤ 0.0001) higher than both under Hashab (321.8 kg/ha and the control (454.8 kg/ha). Trees vary in their capacity to induce changes in soil pH, OC, ECe whereas effects on soil K, P and N were not substantial. In this respect, the Hashab tree was found to contribute much higher amounts of OC to the soil. Initial dry matter weight loss during decomposition of the tree litter varied significantly (P ≤ 0.04) between the different sources and was found to be in the order of Hashab > Neem > Heiglig. The decomposition study also found that tree litters do not vary significantly in their potential to release N and P. However, K in all litters was the rapid element to be mobilized. It is concluded that the capacity of trees to improve soil fertility in the nutrient poor sandy soils could offer an alternative management system for improved cultivation of field crops. iii However, due to high initial P content, Neem tree could be a good source for enriching soil with P. iv ﻣﻠﺨﺺ ﺍﻟﺒﺤﺚ ﺗﺴﺎﻋﺪ ﺍﻷﺷﺠﺎﺭ ﰲ ﲢﺴﲔ ﺧﺼﻮﺑﺔ ﺍﻟﺘﺮﺑﺔ ،ﻭﺫﻟﻚ ﺑﺘﻐﲑ ﺍﳋﻮﺍﺹ ﺍﻟﻜﻴﻤﻴﺎﺋﻴﺔ ،ﺍﺍﻟﺘﺮﻛﻴﺒﺔ ﺍﻟﻔﻴﺰﻳﺎﺋﻴﺔ ،ﺍﳌﻨﺎﺥ ﺍﻟﺪﻗﻴﻖ ،ﺳﻌﺔ ﺍﻟﺘﺸﺮﺏ ﻭﺗﻨﻈﻴﻢ ﺭﻃﻮﺑﺔ ﺍﻟﺘﺮﺑﺔ .ﺍﺟﺮﻳﺖ ﲡﺮﺑﺘﺎﻥ ﺣﻘﻠﻴﺘﺎﻥ ﰱ ﻭﻻﻳﺔ ﺟﻨﻮﺏ ﻛﺮﺩﻓﺎﻥ)ﰲ ﺍﻟﻔﺘﺮﺓ ﻣﺎ ﺑﲔ ﻳﻮﻟﻴﻮ ﺣﱴ ﻧﻮﻓﻤﱪ( ﻭﺫﻟﻚ ﳌﻌﺮﻓﺔ ﻭﲢﺪﻳﺪ)ﰱ ﺍﻟﺘﺠﺮﺑﺔ ﺍﻷﻭﱃ( ﻣﺴﺎﳘﺔ ﺍﻷﺷﺠﺎﺭ ﺍﻟﺜﻼﺛﺔ ﺍﳌﻨﺘﺨﺒﺔ)ﻫﺠﻠﻴﺞ ،ﻧﻴﻢ ﻭﻫﺸﺎﺏ( ﶈﺼﻮﻝ ﺍﻟﺪﺧﻦ ﻭﻣﻌﺮﻓﺔ ﻧﻮﻋﻴﺔ ﺍﻟﺘﺮﺑﺔ ،ﻭﺍﻳﻀﺎ ﳌﻼﺣﻈﺔ)ﰱ ﺍﻟﺘﺠﺮﺑﺔ ﺍﻟﺜﺎﻧﻴﺔ( ﲢﻠﻞ ﺑﻘﺎﻳﺎ ﺍﻭﺭﺍﻕ ﺍﻷﺷﺠﺎﺭ ﻭﻣﻌﺮﻓﺔ ﺍﻟﻌﻨﺎﺻﺮ ﺍﳌﺘﺤﺮﺭﺓ ﻣﻨﻬﺎ. ﺍﻇﻬﺮﺕ ﺍﻟﻨﺘﺎﺋﺞ ﺍﻥ ﺍﻧﺘﺎﺟﻴﺔ ﺍﻟﺪﺧﻦ ﲢﺖ ﺍﺷﺠﺎﺭ ﺍﻟﻨﻴﻢ )174.83ﻛﻠﺠﻢ/ﻫﻜﺘﺎﺭ( ﻭﺍﺷﺠﺎﺭ ﺍﳍﺠﻠﻴﺞ)173.09ﻛﻠﺠﻢ/ﻫﻜﺘﺎﺭ( ﺍﻋﻠﻰ ﻣﻦ ﺍﻧﺘﺎﺟﻴﺘﻪ ﰱ ﺍﻟﺸﺎﻫﺪ )121.43ﻛﻠﺠﻢ/ﻫﻜﺘﺎﺭ( ﲟﻌﺪﻝ .%43 ﺍﻗﻞ ﺍﻧﺘﺎﺟﻴﻪ )111.04ﻛﻠﺠﻢ/ﻫﻜﺘﺎﺭ( ﺳﺠﻠﺖ ﲢﺖ ﺍﺷﺠﺎﺭ ﺍﳍﺸﺎﺏ .ﻭﰱ ﺣﲔ ﺍﻥ ﻭﺯﻥ ﺍﳌﺎﺩﺓ ﺍﳉﺎﻓﺔ ﻟﻘﺼﺐ ﺍﻟﺪﺧﻦ ﲢﺖ ﺍﳍﺠﻠﻴﺞ )1161.5ﻛﻠﺠﻢ/ﻫﻜﺘﺎﺭ( ﻭﺍﻟﻨﻴﻢ 857.8ﻛﻠﺠﻢ/ﻫﻜﺘﺎﺭ( ﺍﻋﻠﻰ ﻣﻨﻬﺎ ﲢﺖ ﺍﺷﺠﺎﺭ ﺍﳍﺸﺎﺏ )321.8ﻛﻠﺠﻢ/ﻫﻜﺘﺎﺭ( ﻭﺍﻟﺸﺎﻫﺪ )454.8ﻛﻠﺠﻢ/ﻫﻜﺘﺎﺭ(. ﲣﺘﻠﻒ ﺍﻷﺷﺠﺎﺭ ﰱ ﻣﻘﺪﺭﺎ ﻻﺣﺪﺍﺙ ﺗﻐﲑﺍﺕ ﰱ ﺍﳊﻤﻮﺿﺔ ،ﺍﻟﻜﺮﺑﻮﻥ ﺍﻟﻌﻀﻮﻯ ﻭﺍﳌﻠﻮﺣﺔ ﺑﺎﻟﻨﺴﺒﺔ ﻟﻠﺘﺮﺑﺔ. ﺑﻴﻨﻤﺎ ﺗﺄﺛﲑﺍﺕ ﺍﻟﺒﻮﺗﺎﺳﻴﻮﻡ ،ﺍﻟﻔﺴﻔﻮﺭ ﻭﺍﻟﻨﻴﺘﺮﻭﺟﲔ ﺗﻌﺪ ﻏﲑ ﺍﺳﺎﺳﻴﺔ ،ﰱ ﻫﺬﺍ ﺍﻟﺴﻴﺎﻕ ،ﻭﺟﻮﺩ ﺷﺠﺮﺓ ﺍﳍﺸﺎﺏ ﻟﻠﻤﺴﺎﳘﺔ ﺑﻘﺪﺭ ﺍﻛﱪ ﻣﻦ ﺍﻟﻜﺮﺑﻮﻥ ﺍﻟﻌﻀﻮﻯ ﰱ ﺍﻟﺘﺮﺑﺔ. ﻓﻘﺪﺍﻥ ﻭﺯﻥ ﺍﳌﺎﺩﺓ ﺍﳉﺎﻓﺔ ﺍﻷﻭﱃ ﺧﻼﻝ ﻓﺘﺮﺓ ﲢﻠﻞ ﺍﻭﺭﺍﻕ ﺍﻷﺷﺠﺎﺭ ﳜﺘﻠﻒ ﺑﺎﺧﺘﻼﻑ ﺍﳌﺼﺎﺩﺭ ﺣﻴﺚ ﻭﺟﺪ ﺗﺮﺗﻴﺒﻪ ﻋﻠﻰ ﺍﻟﻨﺤﻮ ﻫﺸﺎﺏ ﻳﻠﻴﻪ ﺍﻟﻨﻴﻢ ﰒ ﺍﳍﺠﻠﻴﺞ .ﺩﺭﺍﺳﺔ ﺍﻟﺘﺤﻠﻞ ﺍﻳﻀﺎ ﻭﺟﺪﺕ ﺍﻥ ﺍﻭﺭﺍﻕ ﺍﻷﺷﺠﺎﺭ ﻻﲣﺘﻠﻒ ﺑﺼﻮﺭﺓ ﻭﺍﺿﺤﺔ ﰱ ﳏﺘﻮﻳﺎﺎ ﻻﻃﻼﻕ ﺍﻟﻨﻴﺘﺮﻭﺟﲔ ﻭﺍﻟﻔﺴﻔﻮﺭ ،ﺑﻴﻨﻤﺎ ﺍﻟﺒﻮﺗﺎﺳﻴﻮﻡ ﻳﻌﺪ ﻋﻨﺼﺮﺍ ﺳﺮﻳﻌﺎ ﰱ ﻛﻞ ﺍﻷﻭﺭﺍﻕ ﻟﻸﺷﺠﺎﺭ ﺑﺎﻟﻨﺴﺒﺔ ﳊﺮﻛﺘﻪ. ﻫﺬﺍ ﳜﻠﺺ ﺑﺄﻥ ﻣﻘﺪﺭﺓ ﺍﻷﺷﺠﺎﺭ ﰱ ﲢﺴﲔ ﺧﺼﻮﺑﺔ ﺍﻟﺘﺮﺑﺔ ﺑﺎﻟﻨﺴﺒﺔ ﻟﻠﺘﺮﺏ ﺍﻟﺮﻣﻠﻴﺔ ﺍﻟﻔﻘﲑﺓ ﻟﻠﻌﻨﺎﺻﺮ ﻳﻌﻄﻰ ﻧﻈﺎﻡ ﺍﺩﺍﺭﻯ ﺑﺪﻳﻞ ﻟﺘﺤﺴﲔ ﻭﺗﻄﻮﻳﺮ ﺍﶈﺎﺻﻴﻞ ﺍﳊﻘﻠﻴﺔ.ﻋﻠﻴﻪ ﻭﺧﻼﻝ ﺍﶈﺘﻮﻯ ﺍﻷﻭﱃ ﺗﻌﺘﱪ ﺷﺠﺮﺓ ﺍﻟﻨﻴﻢ ﻣﺼﺪﺭ ﺟﻴﺪ ﻟﺘﻐﺬﻳﺔ ﺍﻟﺘﺮﺑﺔ ﺑﺎﻟﻔﺴﻔﻮﺭ v Table of content Dedication Acknowledgment Abstract Arabic Abstract Table of contents List of tables List of figures Chapter One: Introduction Chapter Two: Literature review 2.1 Agroforetry as atool for sustainable agriculture 2.1.1 General 2.1.2 Forest loss and soil degradation in the tropics 2.2 Contribution of tree to soil fertility 2.2.1 General 2.2.2 Tree on farm and their contribution to soil fertility 2.2.3 Main tree types (Heiglig, Neem and Hashab) 2.2.4 Effect of trees on soil biology 2.3 Effect of specific trees on soil properties (Mesquite) 2.4 Effect of afforestation and deforestation on soil properties 2.4.1 General 2.4.2 Effect on soil carbon 2.5 Tree crop interaction 2.6 Decomposition of tree litters 2.6.1 Patterns of decomposition and carbon, nitrogen, and phosphours dynamics of litter in upland forest and peat land 2.7 Importance of efficient use of rainfall Chapter Three :Material and methods 3.1 Location of study area 3.2 Climate 3.3 Topography 3.4 Soil 3.5 Vegetation 3.6 Agriculture 3.7 Experiment layout 3.8 Soil analysis 3.9 Plant analysis 3.10 Calculation Chapter Four : Results vi Page i ii iii v vi viii ix 1 5 5 5 6 10 10 11 13 18 19 20 20 21 23 24 26 28 30 30 30 31 31 32 34 34 37 37 38 40 4.1 Main experiment 4.2 Secondary experiment Chapter Five : Discussion 5.1 Cultivation of millet under different tree species 5.1.1 Effect on yield and straw dry matter 5.2 Decomposition and nutrients release 5.2.1 Dry matter weight loss(DMW) 5.2.2 Nutrients release Chapter Six : Conclusions and Recommendations 6.1 Conclusions 6.2 Recommendations References vii 40 54 64 64 64 69 69 69 72 72 73 74 List of tables 3.1 3.2 4.1 4.2 4.3 Some selected soil physical and chemical properties of the study sit.. 32 Characterization of the plant used…………………………………….36 Effect of trees on yield of millet………………………………………40 Effect of trees on dry matter content of millet………………….….…41 Actual changes of percent dry matter weight remaining of …….……56 Heiglig (H), Neem(N) and Hashab (S) during the period of 10 weeks of decomposition 4.4 Actual changes of percent remaining N of Heiglig (H), Neem(N)…….58 and Hashab (S) during the period of 10 weeks of decomposition 4.5 Actual changes of percent Phosphorus remaining of Heiglig(H), …….60 Neem(N) and Hashab(S) application during the period of 10 weeks of incubation 4.6 Actual changes of percent Potassium remaining of Heiglig(H)…….…62 , Neem(N) and Hashab(S) application during the period of 10 weeks of incubation. 4.7 Actual changes of ash remaining of Heiglig(H), Neem(N) and………63 Hashab(S) application during the period of 10 weeks of incubation. viii List of figures 4.1 Effect of trees on soil pH in the 0-20 (a), 20- 40…………..43 (b) and 40- 60 (c) cm depths 4.2 Effect of trees on ECe (dSm-1) in the 0-20 (a), 20- 40 …….45 (b) and 40- 60 (c) cm depths 4.3 Effect of trees on ECe (dSm-1) in the 0-20 (a), 20- 40……..47 (b) and 40- 60 (c) cm depths 4.4 Effect of trees on TN (%) in the 0-20 (a), 20- 40 ……..…..49 (b) and 40- 60 (c) cm depths 4.5 Effect of trees on Total P (ppm) in the 0-20……………….51 (a), 20- 40 (b) and 40- 60 (c) cm depths 4.6 Effect of trees on Total soluble k (meqL-1) in the 0-20……53 (a), 20- 40 (b) and 40- 60 (c) cm depths ix CHAPTER ONE Introduction Traditionally, soil quality has been mainly associated with forest production (Hornik 1992), whereas more recently the definition has been expanded to include the capacity of a soil to sustain biological productivity, maintain environmental quality, and promote plant and animal health (Doran & Parkin 1994). Moreover, it has been established that more dynamic characteristics such as microbial biomass, soil enzymes activity, soil respiration and other biological indices respond more quickly to changes in management or environmental conditions than characteristics such as soil organic matter and total nitrogen (Brookes 1995; Trasar et al. 1998). Trees tend to improve the site by changing the soil chemical properties, physical structure, microclimate, infiltration capacity and moisture regime of the soil (Prinsely and Swift, 1986). With time, process such as litter fall, nitrogen fixation, root extension, crown expansion and nutrient cycling contribute to nutrient and organic matter build-up in the top soil leading to physical, chemical and biological improvement in the critical rooting zone (Gill et al., 1987; Gill and Abrol, 1991; Evans, 1992; Garg and Jain, 1992). Agroforetry has been defined as "tree plus any other food crop” 1 or, alternatively as land management "comprising trees with a form of food crops” (Mac Dicken and Vergara 1990; Vergara 1985). Agroforestry, also is considered a collective term for those land use practices in which trees and shrubs are combined deliberately on a land unit with the agricultural crops and\ or livestock in spatial arrangements or temporal sequences (Rain tree 1987). A more comprehensive definition that Agroforestry is considered to be any land use that maintains or increase total yields by combining food crops, livestock production and forest crops on the same unit of land. Alternately or simultaneously, using management practices that suit the social and cultural characteristics of the local people, and the ecological and economic condition of the area (Young 1983). The region of south Kordofan is characterised by a wide diversification of vegetation cover and infertile sandy soil is dominated in north side of the state where some crops such as millet is cultivated. It was observed that the yield of annual crops associated with these trees is not similar. Therefore, there is a need to determine the factors that contribute to such variations. From this point of view, we set this research study with the main objective of determination of the contribution of trees to soil 2 amelioration and yield of millet crops in nutrients poor sandy soils. 3 Specific objectives include: 1. Determination of the effect of trees on soil quality attributes (chemical and physical). 2. Monitoring decomposition and nutrients (N, P and K) release from litters of Acacia senegal (Hashab), Blanites aegyptiaca (Heglig) and Azadirachtica indica (Neem). 3. To determine the effects on yield of millet (Penesitum typhoidium) 4 CHAPTER TWO Literature Review 2.1. Agroforestry as a tool for sustainable agriculture: 2.1.1 General A variety of agricultural and natural resource production systems are recognized and practiced in the dry land regions of the world. Depending upon the environmental and socioeconomic situation, these production systems vary from traditional agricultural crop and livestock production systems to different combinations of agricultural, livestock, forestry. and other productions systems that are practiced either rotationally. simultaneously, or spatially on the same piece of land. Regardless of the nature of these combined production systems, their goal is to provide ecological stability and sustainable benefits to users of the land. Combined production systems that involve trees or shrubs are known more commonly as agroforestry systems. Although new to many people. agroforestry is not a new concept of land use. Historically it has been a common practice to cultivate tree or shrub species and agricultural crops in intimate combinations. Worldwide examples of agroforestry are numerous ranging from practices in the middle ages in Europe before colonial times in 5 America, Asia, and Africa (King 1989). Agroforestry was largely a "handmaiden" of forestry in its early history. while today it is recognized set of systems that are capable of yielding food and wood and at the same title conserving and when necessary rehabilitating ecosystems. 2-1-2:Forest loss and soil degradation in the tropics: Tropical forests cover less than 6% of the Earth’s land area but contain the vast majority of the world’s plant and animal genetic resources. It is estimated that the tropical rain forest may contain 30 million plant and animal species. People depend on forests and trees in the developing countries in many different ways (Dubois 2003):- one fourth of the world’s poor depend directly on forests for their livelihood; - 350 million people live in or adjacent to dense forests and rely on them; - At least 2 billion people rely on biomass fuels (mainly fuelwood) for cooking and heating; - Forestry provides employment for more than 10 million people; - Natural products from forests are the only source of medicine for 7590% of people in the world. Shifting cultivation is believed to have originated around 7000 BC, and this system is still common in the mountainous areas of tropical Asia, and in Africa and Latin America. It was predominantly sustainable in the past due to a low population pressure and the availability of large forest areas. Today, shifting cultivation contributes to excessive soil erosion and to land degradation (Steppler and Nair 1987). It is estimated that 500 million farmers in developing countries still use shifting cultivation systems (Scherr 1999). 6 Most of them cultivate their land in marginal areas with poor soil quality, or on steep slopes. Shortening fallow periods and widespread burning to control weeds and pests further contribute to land degradation. Large areas have already been abandoned due to nutrient and organic matter depletion or invasive weeds (Scherr 1999). Soils on steep slopes have commonly completely lost their productivity due to soil erosion. This causes serious local food shortages (Sah 1996). Productivity has declined 16% on the African agricultural lands in the past 50 years. Of the degraded soils, 58% are in drylands and 42% in humid areas. The most common reason for declining productivity is water erosion. Other reasons are wind erosion, chemical soil degradation (loss of nutrients, salinization, pollution, and acidification) and physical soil degradation (loss of organic matter, water logging, and compaction sealing or crusting. The extent and effect of water erosion depend on the soil erosivity, which is the power of the rain to cause erosion; and erodibility, which is the ability of the soil to resist the rain (Hellin 2006). Water erosion is problematic in the tropics because of heavier rain showers, as compared to other regions. Erosion is caused in the tropics due to uncovered soil, absence of windbreaks, lack of organic matter in the soil, and monocultures in farming (Glover 2005). The highest erosion rates in Africa have been calculated in the Maghreb region, East African highlands (including the East Usambara Mountains), eastern Madagascar, and parts of Southern Africa (Scherr 1999). Soil degradation is a major contributor to nutrient losses, because most of the scarce soil nutrients in the tropics are in the top 5-10 cm of the soil (Nkonya et al. 2004). The soils have a low water holding capacity due to a low content of small soil particles. High temperatures favour rapid 7 decomposition of organic residues; thus organic inputs are needed to avoid erosion. Steep lands are more sensitive to rapid soil degradation through runoff (Hellin 2006). Soil fertility depletion on smallholder farms in Africa is already considered as a biophysical limiting factor affecting food production (Sanchez et al. 1997). This soil degradation affects more the rural poor, because they are more dependent on annual agricultural crops that also cause more degradation than the other crops. They also rely more on common-property lands, which often are most seriously degraded. During the present field work local farmers in the 8 Population increase Shortage of land Shortening of fallows Lack of capital Decline in fertility Low crop yields Shortage of food or Low inputs Sloping land Soil erosion Intensive land use Decline in fertility Low crop yields Shortage of food or Lack of conservation Figure 1. Chains of cause and effect linked to decline in soil fertility (UNDP 1995. 9 2.2. Contribution of trees to soil fertility: 2-2-1:General : The properties of forest soils are connected immediately with the type and chemical composition of the forest humus they contain. The chemical nature of forest humus layers plays an important role in the storage and cycling of nutrients (Snyder and Pilgrim 1985). Equally significant is the impact of forest litter and humus on the processes of soil genesis (Duchaufour 1976). The organic matter of forest soils is formed during humification of plant litter, resulting in the formation of three main types of forest humus-mull, moder, and mor, which are determined by the rate of decomposition. The humification process can be followed starting from the natural plant biopolymers. Studies on the quantitative organic chemical composition of forest litter are scarce (Mangenot and Toutain;. 1980), depite the significance of the nature of the parent litter material on the formation of humic compounds, and hence on the quality of forest humus. Conventionally, the chemical composition of litter is divided into four classes: water-soluble compounds, lipids, polysaccharides (cellulose and hemicelluloses), and lignin. These are analyzed by the classical method of successive 10 extractions developed by Waksman and Tenney (1927) and modified by Blume (1965). Mangenot and Toutain (1980) summarized existing data on litter composition and found large differences for contents of cellulose, hernicelluloses, and lignin of several litter types. According to Berthelin and Toutain (1982) and Swift et al (1979), these variations are related not only to differences in the overall litter composition, but mainly to inadequate organic chemical analysis. 2-2-2:Trees on farm and their contribution to soil fertility: Among these tree species, Cordia africana Lam. And Croton macrostachyus Del. are commonly grown in association with crops in many places in Ethiopia including Badessa area. Edwards et al. (1995) and Negash (1995) reported the biology, germination, propagation, uses and distribution of these species. Both species are less vulnerable to drought compared with eucalypts that are re- garded as drought tolerant (Gindaba et al. 2004a) and grow fairly comparable to the eucalypts if moisture is available (Gindaba et al. 2005). Studies by Nyberg and Högberg (1995), Ashagrie et al. (1999) and Yadessa; et al. (2001) reported positive influence of C. macrostachyus and C. africana on various soil fertility parameters. In mixed-farming systems where trees and crops grow 11 in combination, various types of interactions take place between the associates (Nair 1993; Van Noordwijk et al. 1996; Young 1997). According to Van Noordwijk et al. (1996), a tree with a deep root system, having limited lateral extension in the surface soil, is ideal from a nutrient cycling perspective due to the low competition for nutrient and moisture uptake with annual or perennial crops. However, the competition of trees with annual crops is only seasonal and is restricted to the crop root zone (Young 1997). Farmers usually amputate lateral tree roots during tillage and hoeing to discourage the interference of tree roots with crop roots. In addition to root cutting, seasonal shoot pruning and pollarding could also influence root development and the contribution of the trees to underneath soil (Schroth and Zech 1995). Trees on croplands have been reported to improve soil fertility due to their organic inputs with nutrient recycling through mineralization (Nair 1993; Mwiinga et al. 1994; Young 1997; Nyberg 2001; Gindaba et al. 2004b). Comparison of soils from under tree canopy and areas away from the influence of the trees has been used to study the influence of trees on soils (Nyberg and Högberg 1995; Young 1997; Yadessa et al. 2001; Nyberg 2001). However, no studies were made to investigate the lateral distributions of roots of C. africana and C. macrostachyus and their influences on soil nutrient reserve. In Badessa 12 and other areas where the tree cover of croplands are drastically declining with subsequent loss of fertility, knowledge of the contribution of trees to soil fertility is vital to encourage tree planting by individual farmers . 2.2.3. Main tree types (Heiglig, Neem, Hashab): * Blanites aegyptaca (Heiglig): Description: A small to medium sized tree generally reaching 10 miters in height, and rarely goes over 15 miters. This tree is an evergreen which losses its leaves only when very dry. Older trees are recognizable by the bark which has deep vertical fissures running the length of the trunk. The crown of the tree is frequently characterized by drooping young branches. Thorns occur singly and are often over 8 cm log. Distribution: Balanites aegyptiaca is found in Africa in most Arid to sub-humid area north of Zimbabwe. It is wide spread throughout the Sahel and Sudan. The tree is used for fuel wood , amenity, sand dune control, medicine , charcoal , shelter belt, shade , pesticide , fodder , timber , agroforestry and fruit hedging (live and dead). Tree requirements: The tree requires rainfall of about 200 13 ___ 800 mm in a year. However, in areas with lower rainfall this species requires a high water table and initial irrigation. Soil type: Heiglig adaptable to all soil types including sandy, heavy clay, and skeletal soils. Altitude: 380 to 1500 m above see level. Temperature: The tree tolerates extremely high temperatures. Propagation: 500____1500 seeds/kg. The flesh of the fruit should be removed by soaking or washing or it can be eaten .Seed can be directly sown into polythene bags, although germination is enhanced if they are first soaked in cold water for 2 - 3 days. Germination takes 3 - 4 weeks and the germination rate can reach up to 70%. This tree is a valuable and highly recommended tree, despite its slow growth rate. Easily established (especially through direct seeding), and although initial protection is required, it is relatively maintenance-free once rooted. This has been studies by: (Andrews (1956); National Academy of sciences (1980); Von maydell (1986);Vogt (1976); Branney (1989); Wickens (1990); Hamza (1990); Mahony (1990) ). 14 * Azadirachta idica (Neem) Description: The Neem tree is an ever green tree reaching maximum height of 20 m. The leaflets enable easy recognition; they are serrulate and have very bitter, quinine –like taste. Flowers occur in panicles and are small, white to yellow in color, and fragrant. It is universally known by the Indian name (Neem). Distribution: Neem originates from Asia, in particular north east India and naturalized throughout the tropics including Sudan. The tree used for fuel wood, amenity, shelter belt, oil, timber, pesticide, hedging, fruit, medicine and agroforestry. Tree requirements: For establishment, the tree required rainfall of about 400__ 1200 mm in a year. In the presence of high water table, less than 200 mm will be satisfactory for tree establishment or in some cases, if suitable water harvesting techniques are carried out. The tree does not withstand water logging. 15 Soil type: The Neem tree grows in a wide range of conditions, i.e. from sandy to heavy clay soils and also on stony and nutrient poor sites. Temperature: Neem tree tolerates very high temperatures but sensitive to lower temperature degrees (Reference). Propagation: about 5.000 seed/kg. This tree is becoming increasingly popular in the Sahel zone due to its many benefits that mentioned above. This has been studies by: (Tirkul (1984), Von Maydell (1986), Kerkhof (1988), Branney (1989), Hamza (1990), Mahoney (1990), Apdein (1991) personal communication) . * Acacia senegal (Hashab): Description: Acacia senegal is a shrub or small tree approaching 8 m in height and well known for its gum Arabic .This Acacia species is most readily distinguished by its black thorns, that occur in groups of 3 (not in pairs like most other acacia species), with two side thorns curved upwards and the middle one curved downwards, and measuring roughly 0.5 cm in length. 16 Distribution: The tree is typically associated with the Sahel zone and it occupies an area from the red Sea to Senegal. Different varities are also found in east and southern Africa. Also, it has been introduced and naturalized in Asia. The tree used for Fuel wood, amenity, dune control, gums, charcoal, shade, shelter belt, honey, timber, pesticide, fodder, fruit, medicine, hedging, agroforestry. Tree requirement: In the sandy soils, the tree requires rainfall of about 300 to 700 mm/year whereas in the clay soils it requires about 450 mm. Soil type: The tree prefers sandy soils. It will also grow on loamy sands and, in places of higher rainfall, on clays. Temperature Acacia tolerates very high temperatures and very sensitive to frost. It is propagated by seeds at a rate of 8.000-10.000 seeds/kg, Most production takes place in nurseries and seeds should be collected from a good parent stock and if treated with an insecticide will remain viable for at least a year (from one growing season to the next). Sowing can be directly into unshaded pots without any pre-treatment. Germination usually starts after three days and is complete within a week. As it is a fast growing species, 17 total nursery time may be as little as three months. The tree coppices well which is an important point in its favour, when coppicing, stem should be cut at as lant to allow for rainfall runoff and thus prevent rotting. This has been studies by: (Andrews(1956); National Academy of sciences (1980); Wickens (1980); Thirakul (1984); Von Maydell (1986); Vogt (1987); Hamza (1990); Paulos and Abdein (1990). 2-2-4:Effects of trees on soil biology: The influence of different plant species on soil microbial properties has been of interest for decades initially with respect to microbial biomass and activities in stands with different dominant tree species ( Turner et al., 1993; Bauhus et al., 1998 ) and more recently in identifying changes in microbial community composition in the forest floor ( Myers et al., 2001; Priha et al., 2001; Grayston and Prescott, 2005; Hackl et al., 2005 ), in grasslands ( Bardgett and McAlister, 1999; Grayston et al., 2001 ) or in particular ecosystems such as deglaciated terrain and cut-away peatland ( Bardgett and Walker, 2004 ; Potila et al., 2004 ). However, while it is well established that plants have species-specific effects on their associated living microbial biomass, activity and communities, little is known about the degree to which soil microbial residues persist and differ in forest floors under different tree species. Persistence of microbial residues may 18 be an important control over carbon and nitrogen cycling or storage in forest soils ( Balser, 2005 ). Amino sugars are important microbially de rived residues that can be quantified in forest soils to provide information about the fate of carbon and nitrogen within biomass of bacteria and fungi, in turn indicating relative microbial contribution to carbon and nitrogen cycling ( Parsons, 1981; Amelung, 2001). Plants do not synthesize significant amounts of amino sugars, and amino sugars are stable against fluctuations in living microbial biomass (Nannipieri et al., 1979; Chantigny et al., 1997 ). Further, following cell death, amino sugars are significantly stabilized in soils, and accumulate over time (Guggenberger et al., 1999 ; Glaser et al., 2004 ). 2-3:Effects of specific tree on soil properties (Mesquite): Build up of soil organic carbon is only possible with additions of both organic matter and nitrogen. Nitrogen additions are essential to decrease the C/N ratio and facilitate the decomposition of high C/N containing dry matter such as grasses. As soil organic matter degradation is much more rapid above 35.3 oC than at lower temperatures (Jenny, 1944), and as savanna trees decrease soil temperatures by 5–12.3 oC (Belsky et al., 1993), the shading effect of trees helps build soil organic matter. There has been controversy in the literature regarding the cause of the 19 islands of fertility surrounding nitrogen fixing trees in arid regions (Scholes & Archer, 1997; Belsky et al., 1993; Weltzin & Coughenour, 1990). Despite the fact that trees such as Prosopis can fix N, some workers (Garcia-Moya &McKell, 1970; Barth & Klemmedson, 1982) have suggested that the increased nutrients under the canopies is simply a redistribution of nutrients from deeper in the profile and outside the canopy. However, Rundel et al. (1982) conclusively demonstrated that Prosopis glandulosa in the California desert fixed about 30 kg N ha~1year~1 which is about 15 times the annual deposition of N in west Texas (Loftis & Kurtz, 1980). Johnson & Mayeux (1990) found nodules on 19 mesquites at five locations in the eastern portions of mesquite’s range. 2.4. Effects of afforestation and deforestation on soil properties: 2-4-1: General: The complex integration of the primary natural resources, soil, water and vegetation, is vital to maintaining terrestrial ecosystem functions and productivity (Islam & Weil, 2000). Land use changes may influence many natural phenomena and ecological processes, including soil nutrient and soil water change (Fu et al. 1999, 2000). Characterizing soil nutrients in relation to land use types and history is important for understanding how 20 ecosystems work and assessing the effects of future land use change (Wang et al. 2001). Soil nutrient status can be changed where forest is cleared for agricultural cultivation, allowed to revert to natural vegetation or replanted to perennial vegetation (Lepsch et al., 1994; Moran et al., 2000). During the last 50 years, as a result of increasing demand for wood timber, pasture, shelter and food, natural land covers, particularly forests, are being converted to cropland at an alarming rate in southwestern China, particularly in Sichuan province. 2.4.2. Effects on Soil carbon: Due to the low activity of the mineral phase and the restrictive chemical conditions commonly found in soils of wet tropical regions, soil organic carbon (SOC) plays major role in virtually all edaphological processes, from aggregation to plant nutrient supply, and its importance is expected to increase in the less fertile and coarse-textured soils. When in initial, usually labile form (litter and debris), organic matter is a source of energy, carbon and mineral nutrients for soil fauna and micro biota, and may contain a major part of the plant-available nutrient reserve of the soil (Zinn, 1998). Additionally, the by-products of organic decomposition play a decisive role in phenomena such as soil aggregation, chemical buffering and CEC (Silva et al., 1994; Mendonca and Rowell, 1996), when at an 21 intermediate (sugars, polysaccharides, amino sugars, etc.) or advanced stage of chemical alteration (humic substances). The conservation of SOC may be considered a critical factor for the sustainability of land use systems in the tropics, and it also represents an effective way of reducing the agricultural emissions of CO2, and may even be a sink for the anthropogenic atmospheric excess of this greenhouse gas (Lat;. 2001). Nevertheless, many authors report that substitution of native vegetation by agricultural systems leads to depletions in SOC content, primarily due to accelerated decomposition rates caused by soil tillage, which enhances aeration and physical contact to decomposer organisms (Silva et al., 1994; Resck et al., 2000). In the long run, SOC losses may affect crop yields by reduction of nutrient supply from labile forms and organic- dependant CEC. Despite the importance of organic carbon in soils of Brazil and other tropical countries, most research on the subject refers to litter and soil carbon quantification, although studies of SOC dynamics and is chemical characterization in natural and agricultural ecosystems have been given increasing attention (Volkoff et al., 1988; Bravard and Righi, 1991; Nascimento et al., 1992). A fforestation with exotic, fast-growing tree species such as Eucalyptus spp. And Pinus spp. is an important economical activity in many tropical countries, in order to supply wood for industry, energy and farm purposes, 22 and plantation areas may often be very large. Once a fforestation does not require annual or constant tillage and cultivation, it is normally considered a conservation land use system when compared to croplands, even if short rotation cycles (>7 years) are used. Nevertheless, the environmental impacts of this practice, such as on hydrology and soil properties have been a concern in many parts of the world (Lima, 1996). However, the alterations caused in tropical soils through a fforestation with fastgrowing trees are not yet fully understood, and literature frequently reveals opposite conclusions about processes and effects, especially in SOC dynamics and Properties. 2.5. Tree crop interaction: The benefit of deep-rooted vegetation for maintaining ecosystem functioning is a major attraction for using agroforestry for sustainable land and water management in areas where high energy input large scale agriculture is impractical (Kidd and Pimentel, 1992) As in Australia, removal of native perennial vegetation and its replacement by shallow rooted annual crops and pastures in many tropical countries has led to a profound change in the pattern of energy capture by vegetation and to hydrological imbalances. In the Sahel, removal of vegetation with deep roots has led to increased drainage from 10-20 to 200-300 mm per year and leaching of nitrate to the water table (Edmunds, 1991; Deans et al., 1995). On the sandy soils of Niger, unfertilized millet fields utilize only 616% of the total rainfall in a watershed and the remainder is lost a run-off, 23 drainage or through soil evaporation (Rockstrom, 1997). In this paper it is intended to review recent evidence of how agroforestry may be able to improve the efficiency with existing land and water are currently used, with the ultimate aim of achieving sustainability of production and resource use. Because much of the future increase in food and wood production in the tropics, necessary for the needs of increasing populations, will have to be achieved from land and water resources already in use, agro forestry is one of the promising options (Young, 2000). Examples from the semiarid tropics, where average land holdings are rapidly declining (1-2 ha compared to 1000-2000 ha in Australia) but, unlike Australia where tree rows are 100-200 m apart (White et al., 2002), it is necessary to integrate tree and crops more closely without compromising the already low crop yield. In particular, they focus on recent attempts to manipulate root function in order to improve spatial complementarily in below- ground resource use and to promote a closer integration of tree and crops. 2.6. Decomposition of tree litters: Plant required more nutrients to take for growth and yield. These nutrients may be released from decomposing residues or animal remains on the soil. The role of trees for soil mulch and livestock feed has been reviewed by 24 Kang et al.,(1990) and Haque et al.,(1995). For instance, understanding the dynamics of availability in soils amended with organic materials could be important in the overall impact assessment on productivity. The efficiency of nutrient transfer from organic inputs to crops could be improved by varying the quality or the time of the application of organic inputs (Swift, 1985). In this context, N derived from legume or harvest residues depends largely on the synchrony between N release from these residues and N demand for uptake by trees. Palm (1995) pointed out that agroforestry species with high N, lignin, and poly phenolic contents may provide nutrient release patterns that more closely match the demands of crops for nutrients, especially N. Myers et al., (1994) stated that, crop residues promote a greater nutrient cycling and improve the synchrony of nutrient cycling and improve the synchrony of nutrient release with crop demand. It was found that in ally cropping system, leucaena mulch and cattle manure agroforestry, maybe a considerable source of N and K for crop growth (Lupwayi and Haque, 1999). 25 2.6.1 Patterns of decomposition and carbon, nitrogen, and phosphorus dynamics of litter in upland forest and peat land: Organic matter accumulates in northern peat lands and other wetlands because the rates of net primary production of vegetation are faster than the rates at which dead plant tissues are decomposed in the soil profile. Net primary production rates in Canadian peat lands are small compared with those of other ecosystems (e.g., Campbell et al. 2000; Moore et al. 2002), so the organic matter accumulation has been linked to slow rates of litter decomposition. Several studies of short-term decomposition rates in peat lands have been made. In these, peat-forming plant tissues have been placed in litterbags, left for several years, and then retrieved. The mass remaining inside the bags is used as an indication of the rate of decomposition. These studies have shown that decomposition rates vary with overall climate (e.g., Hogg et al. 1994), tissue type (e.g., Rochefort et al. 1990; Johnson and Damman 1991), peat land type (e.g., Szumigalski and Bayley 1996; Thormann and Bayley 1997), and placement position within the soil profile (e.g., Belyea 1996). The rate of decomposition of tissues has commonly been assumed to be slower in peat lands than in nearby well-drained upland sites having forest or grassland vegetation. One reason for this assumption is that many peat 26 land litters, especially in bogs, have low nutrient concentrations, particularly nitrogen (N) and phosphorus (P) (e.g., Aerts et al. 1999). Some peat-forming plants, particularly Sphagnum moss, have very slow rates of decomposition (e.g., Clymo 1965) and produce compounds that may slow the rate of microbial activity and tissue decomposition as the peat forms (e.g., Painter 1991; van Breemen 1995). Furthermore, peat lands have a high water table, and the occurrence of flooding (e.g., Day 1983; Lockaby et al. 1996) and anoxic conditions may slow the rate of litter decomposition. The reduction in the rates of CO2 production from peat during the conversion from oxic to anoxic conditions is well established (e.g., Bridgham et al. 1998; Scanlon and Moore 2000). However, in most peat lands, the water table is beneath the peat surface for most of the year, so aboveground litter initially decomposes under oxic conditions before entering the zone beneath the water table. Roots produced at or below the water table may decompose from the outset under anoxic conditions. Frolking et al. (2001) developed a simple peat decomposition model, based on prescribed decomposition rates, peat temperature, and reduction in decomposition upon passage from the oxic to anoxic zones. The authors were able to reasonably simulate organic matter accumulation 27 in several eastern Canadian peat land profiles. Decomposition of litter under anoxic conditions may also affect the release or retention of N and P. Because litter decomposition studies in peat lands and upland forests have usually been conducted separately, there is no clear evidence of whether the site (peat land or upland) is significant in controlling decomposition rates. To test and quantify this, they examined the rates of decomposition of 11 litters placed in three peat land and three nearby upland sites in central Canada, over a 6-year period. The pairs follow a climatic gradient that extends from near the forest–prairie border to the subarctic. they compared the mass remaining after 6 years and the exponential decay model parameter (k) calculated from annual collections over the 6 years. To test whether placement of litter in upland or peat land sites affects the dynamics of N and P during the early stages of decomposition, they also compared the retention, gain, or loss these two nutrients over the 6 years, as a function of the loss of carbon (C). 2.7. Importance of efficient use of rainfall water: Can agro forestry increase productivity through more effective use of rainfall? Cannell et al. (1996) argued that agro forestry may increase productivity provided the trees capture resources which are underutilized by crops. In annual systems where the land lies bare for extended periods, 28 the residual water remaining in the soil after harvest, and off –season rainfall, are often unused, particularly in areas of unimodal rainfall. For instance, at Hyderabad, India (annual rainfall 800 mm) substantial amounts of water remain available below 50 cm depth after harvesting sorghum (Sorghum bicolour) and pigeon pea (Cajanus cajan) (One et al., 1992) and about 20% of the annual rainfall occurs outside the normal cropping season which could be used by perennial species. 29 CHAPTER THREE Materials and Methods 3.1: Location of study area This experiment was carried out in the area north Aldebaibat, near Dilling city, northern part of South Kordufan State (longitudes 28º-0ֿ, 32º- 5 ֿeast and latitudes 10º-0ֿ, 12º- 5 ֿnorth) (South Kordufan survey Office). 3.2: Climate Sudan is known as a dry tropical climate Country. Dilling locality climate is known as savannah tropical climate with high temperature in summer and low temperature in winter. 3.2.1 Temperature Maximum average temperature in summer is between 36oC and 42 oC whereas the minimum temperature is in winter and ranged between 13 oC and 17 oC while the maximum temperature is reached in May. However, the mean temperature is about 35 oC (Salih 2003). 3.2.2: Rainfall: The study area falls within the savannah region and therefore is characterized by seasonal rainfall. The rains start from May until October and the maximum amount is recorded to be in August. Total annual rainfall varies from 400 mm to 650 mm. 3.2.3: Wind: One of the major factors affecting Sudan climate is the inter tropical zone, particularly its movement from north to south and vice area. In winter 30 north east wind blows from November up to April and it’s a dry wind, in summer the prevailing wind is the (south west wind), it causes rainfall during autumn, it is a humid wind, relative humidity in dry season is about 35%, but during the rainy season it reaches about 75% during august. (Salih 2003). 3.3: Topography: Bashir (2003) reported that the height of Nuba Mountains is generally 600 m above sea level. However, the northern parts of the mountains which include Elhamadi, Adebaibat, Sunjukaia and Elfarshaia areas can be considered as flat plains. 3.4: Soil: The soil in the study site is generally sandy soil covering Elhamadi, Adebaibat and Elfarshaia areas; however some chemical and physical properties of the soil are given in Table 3.1. 31 Table 3.1: Some selected soil physical and chemical properties of the study site Soil attribute 0-20 cm 20-40 cm 40-60 cm pH(paste) 5.2 ± 0.49 4.2 ± 0.32 3.9 ± 0.28 ECe (dSm-1) 0.7 ± 0.59 0.97 ± 0.52 0.2± 0.07 O.C (%) 0.2 ± 0.19 0.3 ± 0.28 0.5 ± 0.33 TN (%) 0.5 ± 0.04 0.5 ± 0.49 0.4 ± 0.12 TP (ppm) 9.1 ± 6.26 8.2 ± 3.82 11.2 ± 6.97 K (meq L-1) 0.2 ± 0.02 0.2 ± 0.01 0.2 ± 0.05 Sand (%) 77.5 ± 2.5 76.9± 2.39 76.3 ± 2.04 Silt (%) 8.1 ± 3.15 9.9 ± 3.42 6.9 ± 1.25 Clay (%) 14.4 ± 1.25 13.2 ± 4.61 16.9 ± 1.25 ECe = Electrical conductivity of the saturation extract O.C = Organic Carbon TN = Total Nitrogen TP = Total Phosphours K = Potassium 3.5: Vegetation: The vegetation of the site can be explained in two categories as follows: Division 1: High land vegetation and this in turns can be divided in to two sub-divisions: a) Vegetation covers with great variability because of the variations in elevations from low levels to high levels and with temperature variations at different levels. 32 Species found are: Sterculia setigera(Tartar), Stereospermum Boswellia papyrifera(Tragtarg), kunthianum(Khashkhash), Anogeissus leiocarpus(Sahabb-Silak) and Albizia amara(Arad), ect. b) High land herbs and grasses: Cassia senna (Sennamecca), Cymbopogon nervatus(Nal), Blepharis linariifolia(Begeil), Triagus perteronianus, Echinochloa colona(Difra), Setaria viridis (Lusig), Solanum dubium(Jubain), Cassia occidentalis (Sim Eldabib), Chloris gayana (Afan Elkhadim). Division 2: vegetation of the Khors and Wadies: The area includes khors and Wadies between hills and characterized by a warm climate. High rainfall for short periods always causes run –off and surface floods. The area is also characterized by the dominance of different trees as follow: a) Trees and shrubs; Adansonia digitata (Tabeldi), Diospyros mespiliformis (Jogan), Sesbania spp. (Sesaban), Acacia albida (Haraz), Acacia nilotica (Sunot), Acacia mellifera(Keter), Acacia senegal(Hashab), Acacia seyal(Talih), Dichrostachys cinerea (Kadad), Hyphaene thebaica (Doam), Balanites aegyptiaca(Heiglig), Guria senegalensis(Gubaish), Combertum hartmannianum (Habeal Elgabal) and other Combertum spp. , Ziziphusspinia-chrisi(Sider).etc. b) Grasses of the Wadies It includes annual and perennial grasses like Amaranthus 33 spp(Lissan Eltair), Cenchrus spp(Haskenit), Aristolchia bractealata(Um Galagil), Eragrostis spp(Bano). ect. 3.6: Agriculture: Majority of the people are practicing traditional shifting cultivation and crops grown in the area are millet (Penesitum spp.), ground nut (Arachis hypoaea), Vigen anguiculata(Adasi), Rosette (Hibiscus sabdariffra) and sesame (Sesamum indicum). 3.7: Experiment lay out: Main experiment (1): Effects of trees on soil and yield of millet 3.7.1: Treatments The treatments included the selection of the followings trees: 1 Blanites aegyptiaca (Heglig). 2 Azadirachtica indica (Neem). 3 Acacia Senegal (Hashab). 4 Control (Without trees) To study the effect of some tree species on soil attributes and yield of millet under arid environment. Plots of a size of about 4 m X 4 m were made beside each treatment tree. The plots were arranged in the Randomized Complete Block Design (RCBD) and was replicated four times (therefore, total experimental plots were 16). Millet crop was grown under three species of trees and the control with four replication in each block. The seed rate was 3.15kg per feddan. The plant was irrigated by the rainfall. 34 Parameters The harvest was carried out after 3 month from each plot, 4 plants were removed from the center rows and were immediately weight, oven dried at 70oC and the moisture content was determined. The heads in each plot were removed, dried and the dry matter yield was recorded. Then after, stalks remained in each plot were cut and weighed fresh. The values of moisture content of the samples previously taken were used for calculation of total dry matter accumulation as follows: Total plot dry matter yield (kg/plot) = total plot fresh yield (kg/plot) X (100- moisture content). Total dry matter (kg/ha)= total plot dry matter (kg/plot) X 10000/16 Similarly, the heads weight of the millet from all the replication was determined. Secondary experiment: Decomposition and nutrient release from tree litters This experiment was carried out to support findings from the main experiment using the litterbag technique. 3.7.2: collection of litters from trees From each tree species under which millet was grown, the fresh leaves were removed and used in this study. About 20 gram fresh plant material (whole plant material without grinding) was placed inside the litterbags. A sample from each type was used to determine moisture content and consequently, the content of dry matter added in each litterbag. Each type plant material was replicated four times. Table 3.2 shows some selected mineral composition of the tree leaves used in this experiment. 35 Table 3.2 Characterization of the plant used TN TP K Ash (%) (H) Heiglig (N) Neem (S) Hashab 3.74 0.36 1.2 20 4.24 4.82 1.14 0.4 0.71 0.42 7.43 23 Then after, the litterbags were placed in plots of the three locations and on the surface of the topsoil. The locations were similar to the site of the main experiment where millet was grown. In each plot, 20 litterbags from were placed. After 2, 4, 6, 8, 10 weeks, four litterbags from each plot (four replications) were drawn and each bag was carefully placed inside a paper envelope with a label and transferred to the laboratory for analysis. The samples were air dried and cleaned carefully from attached soil particles. After that the samples were weighed again for determination of the loss of dry matter. Samples were then crushed, grinded to pass a sieve of 0.5 mm and were stored in small nylon envelopes with a label for further analysis. 3.7.3: Soil sample collection After harvest of the main experiment, soil samples were taken from the four sites using the auger, where the experiment was conducted. They were taken at intervals of 0-20, 20-40, 40-60 cm soil depths. Samples were air dried, crushed and sieved through 2mm. sieve and kept for analysis 36 3-8: Soil analysis: 1 The pH value of the soil paste and extract were measured using pHmeter model Kinck digital type 664/ I. 2 The electrical conductivity of the extract (ECe) was measure by Conduct-meter CG 851. 3 Available phosphorus was determined photometric ally by the blue method (Orsen and Cole 1954). 4 Organic carbon was measured by using the modified Walkley Black methods (Walkleyand Black. 1934): 10 ml of K2 Cr2 O7 (1N) and 20 ml of conc. H2 S O4 were added to 0.05 g of soil sample completed to 200ml with distilled water, after awhile 10ml of conc.H3P2O5 (Orthophosphoric acid) and 10 to 15 drops of Diphenylamine were added to 10ml of the pure solution. Then titrated up on ferrous sulphate (0.5N) 5 Potassium was determined according to the flamphotometric described by Chapman and Pratt (1961). 6 Particle size distribution was determined and the textural class was determined according to the American system using textural triangle (Richard, 1954. Chapman and Pratt 1961 et all, 1986). 3-9: Plant analysis: 6 Total nitrogen was determined by the semi-macro Kjeldanhl apparatus 37 (Bremner and Mulvany. 1982): after wet digestion of 0.2 gram of sample by concentrated H2SO4 and gentle heating. Then distillated against HCL (0.1N). 7 Organic carbon was measured by using the modified Walkley black methods. (Walkley and Black. 1934): 10 ml of K2Cr2O7 (1N) and 20ml of conc.H2SO4 were added to 0.05 g of the plant sample completed to 100ml with distilled water, after awhile 10ml of conc.H3P2O5 (Orthophosphoric acid) and two or three drops of Orthophenatroline were added to 10ml of the pure solution. Then titrated up to on ferrous sulphate (0.5N). 8 The samples were ashed at 150 ºC first, then at 550 C and dissolved in HCL (5N) to extract the samples and determine K and P, they were reading by flame photometer and spectrophotometer respectively. 3.10: Calculations: * Percent remaining dry matter after a sampling period was determined as follow: Weight of dry matter at week (e.g. week 2) X 100 Weight of initial dry matter * Percent remaining nutrient (N, P, K): % element at week (e.g. week 2) X 100 % element of initial material X Dry matter added 38 *Statistical differences between treatments were determined using Statistical Analysis System (SAS, 1985) and means were separated using lest significant difference (LSD). 39 CHAPTER FOUR Results 4.1. Main experiment (1): Effects of trees on soil properties and yield of millet 4.1.1 Effect of trees on yield of millet: The effect of trees on yield of millet is shown in Table 4.1. Statistical analysis showed that there were significant (P≤0.03) differences in yield under the different tree species of Heiglig, Neem and Hashab as compared to the control. The results showed that millet yield under the Neem (174.83 kg/ha) and Heiglig (173.09 kg/ha) were higher than the control (121.43 kg/ha) by an average of 43%. The lowest yield (111.04 kg/ha) was recorded under the Hashab trees. Table 4.1. Effect of trees on yield of millet (Average ± standard Deviation). Treatment Yield kgha-1 H (Heiglig) 173.09a ± 51.2 N (Neem) 174.83a ±40.70 S (Hashab) 111.04b ± 4.02 C (Control) 121.43b ± 14.63 Values in columns followed by similar letter (s) are not significantly different at P ≤ 0.05 using Least Significant Difference (LSD) 40 4.1.2 Effect of trees on millet straw DM The effect of trees on millet DMC is presented in Table 4.2. Statistical analysis indicated that there were significant (P ≤ 0.0001) differences in straw DM among the different species of trees. It was found that straw DM in the Heiglig (1161.5 kg/ha) and Neem (857.8 kg/ha) were significantly higher than both under Hashab (321.8 kg/ha and the control (454.8 kg/ha). Therefore, yield under Heiglig trees was higher than that under Neem, Hashab and the control by 35%, 261% and 155%, respectively. Interestingly, yields under Hashab although not significantly different from the control but seemed to be lower (by about 29%). Table 4.2 Effect of trees on dry matter content of millet (Average ± standard deviation) . Treatment Straw Dry matter kgha-1 H 1161.5a ± 147.7 N 857.8b ± 49.61 S 321.8c ± 139.1 C 454.8c ± 126.2 Values in columns followed by similar letter (s) are not significantly different at P ≤ 0.05 using Least Significant Difference (LSD) N: Neem. H: Heiglig S: Hashab. 41 C: Control. 4.1.3 Effect of millet cultivation beside trees on soil chemical properties 4.1.3.1. pH The effect of trees (H, N and S) on soil pH of the 0-20 (a), 20-40 (b) and 40-60 (c) cm soil depths is illustrated in Figure 4.1. Statistical analysis indicates that there were significant differences (P ≤ 0.05) on soil pH in the (a) depth. Soil pH under the Heiglig showed the highest value (4.93) followed by Neem (4.73) followed by Hashab (4.33) whereas the control showed the lowest value (4.13). In the 20-40 cm soil depth, statistical analysis indicated that there were no significant difference between all treatment (C.V= 6.19). The pH of the 40-60 cm depth showed that there were significant (P≤0.05) differences between treatments where soil under the Heiglig showed the highest value (4.45) while Hashab indicated the lowest pH value (3.83). 42 a ab 5 ab 4.5 N b a H S 4 C 3.5 N 4.5 H S C a a a a b N H 4 S C 3.5 N 5 c 4.5 H S C a ab b 4 N b H S 3.5 C 3 N H S C Figure 4.1 Effect of trees on soil pH in the 0-20 (a), 20- 40 (b) and 40- 60 (c) cm depths. Histograms with similar letter (s) are not significantly different at P ≤ 0.05 using Least Significant Difference (LSD) 43 4.1.3.2. ECe The effect of millet cultivation under Heiglig , Neem , Hashab as compared with the control on soil ECe of the 0-20 (a), 20-40 (b) and 4060 (c) cm depths is illustrated in Figure 4.2. Statistical analysis showed that there were significant (P ≤ 0.05) differences between treatments in the (a) depth. The control treatment showed the highest value (1.07) followed by Hashab, Heiglig and Neem was the lowest (0.5). However, for the 20-40 cm and 40-60 cm depths, statistical analysis showed that there no significant effects on ECe values, though values under Neem cultivation showed consistent increase as compared to other treatments. 44 1.5 a ab 1 a a N H b S 0.5 C 0 N 1 a H S a a C a N b H 0.5 S C 0 N 1 a H S a a C a c N H 0.5 S C 0 N H S C Figure 4.2 Effect of trees on ECe (dSm-1) in the 0-20 (a), 20- 40 (b) and 40- 60 (c) cm depths. Histograms with similar letter (s) are not significantly different at P ≤ 0.05 using Least Significant Difference (LSD) 45 4.1.3.2. O.C. The effect of millet cultivation under the different tree species in the content of soil O.C measured at the 0-20 (a), 20-40 (b) and 40-60 (c) cm depths is illustrated in Figure 4.3. In the 0-20 cm soil depth, statistical analysis showed that there were no significant differences in soil O.C content accumulated due to the different treatments, though values determined under Neem trees seemed to be higher. However, in the second depth (i.e. 20-40 cm), results showed there were significant (P ≤ 0.006) variations between treatments in accumulation of O.C. Soils under the Hashab (1.01%) and Neem (0.925) showed the highest values followed by Heiglig (0.432) and the control sowed the lowest value (0.275). At the lower depth (40-60 cm), statistical analysis showed that there was significant (P ≤ 0.01) difference between the treatments with the highest value of (1.15%) recorded in Hashab treatment whereas other treatments showed similar values. 46 1 a a a a 0.8 N 0.6 H 0.4 S C 0.2 0 N b 1.2 1 0.8 0.6 0.4 0.2 0 H S a ab b b S H S 1.2 C C a 1 c N H N 0.8 C b 0.6 b N b H S 0.4 C 0.2 0 N H S C Figure 4.3 Effect of trees on O.C. (%) in the 0-20 (a), 20- 40 (b) and 40- 60 (c) cm depths. Histograms with similar letter (s) are not significantly different at P ≤ 0.05 using Least Significant Difference (LSD) 47 4.1. 3. 3. Total Nitrogen (TN) The effects of millet cultivation on TN in the soil profile are shown in Figure 4.4. In the topsoil (0-20 cm depth), statistical analysis showed that there were no significant difference between treatments. The content of TN varied from 0.40% (under the Hashab tree) to 0.58% (under the Neem trees). In the sub-soil (20-40 cm depth), content of TN was also not different between treatments. However, values seemed to be higher than that determined in the topsoil. Similarly, there were no clear variations in TN observed in the lower soil depth (40-60 cm). 48 a a 0.6 0.5 0.4 0.3 0.2 0.1 0 a a a N H S N H S a a 0.7 0.6 b a C C a N 0.5 H 0.4 S 0.3 C 0.2 0.1 N 0.6 c a H S a a a 0.5 C N 0.4 H 0.3 S 0.2 C 0.1 N H S C Figure 4.4 Effect of trees on TN (%) in the 0-20 (a), 20- 40 (b) and 40- 60 (c) cm depths. Histograms with similar letter (s) are not significantly different at P ≤ 0.05 using Least Significant Difference (LSD) 49 4.1. 3. 4. Total soil P The content total soil P in the soil profile as affected by millet cultivation under different tree species is given in Figure 4.5. Statistical analysis indicates there were no significant differences between treatments in all soil depths. However, it was noticed that P content in the 0-20 and 20-40 cm soil depths seemed to be higher in plots under Heiglig and Neem, respectively. 50 a 12 10 8 a a a a N H 6 4 2 0 S C N 10 a H S a a a 8 b C N 6 H 4 S 2 C 0 N 10 c 8 a H S a a a C N 6 H 4 S 2 C 0 N H S C Figure 4.5 Effect of trees on Total P (ppm) in the 0-20 (a), 2040 (b) and 40- 60 (c) cm depths. Histograms with similar letter (s) are not significantly different at P ≤ 0.05 using Least Significant Difference (LSD) 51 4.1. 3. 4. Total soluble K The content of soluble K in the soil profile determined after harvest of the millet and under the different tree species is shown in Figure 4.6. Results showed that there no statistical variations between treatments in all depths. However, in the lower depth (40-60 cm), K content under the Neem treem was more than double that determined under other treatments, though not significant. 52 0.24 a a a a 0.2 0.16 a N H 0.12 S 0.08 0.04 C 0 N 0.24 0.2 b a H S a a C a N 0.16 H 0.12 S 0.08 0.04 C 0 N 0.24 H S C a 0.2 c N a 0.16 a a H 0.12 S 0.08 C 0.04 0 N H S C Figure 4.6 Effect of trees on Total soluble k (meqL-1) in the 0-20 (a), 20- 40 (b) and 40- 60 (c) cm depths. Histograms with similar letter (s) are not significantly different at P ≤ 0.05 using Least Significant Difference (LSD) 53 4.2: Secondary Experiment: Decomposition and nutrients release 4-2-1: Dry matter weight loss (DMW) Dry matter weight loss from the three trees residues during decomposition was calculated from that remaining in the litterbag in each sampling week. Table 4.3 shows percent remaining of DMW of Heiglig, Neem and Hashb during the 8 weeks of the decomposition period. Results showed that, after two weeks, there was a rapid loss of DM from Hashab litter and it was significantly (P ≤ 0.04) higher than both from Neem and Heiglig. Accordingly, percent remained DM after this period was 71.06, 86.33 and 90.45% for Hashab, Neem and Heiglig, respectively. The decomposition rate constant [(100%-%remained)/time] after this period were calculated to be 5%, 7% and 13% week -1 for Heglig, Neem and Hashab, respectively. In the fourth week, it was observed that DM of Hashab remained almost similar (71.90%) to the second week and without an advanced loss. Whereas loss during the next two weeks from Neem and Heiglig continued rapidly and accounted for about 11% and 12% for Neem and 54 Heiglig, respectively. By the end of this week the amount of DM remained were statistically similar between tree litters. After 6 weeks, statistical analysis showed that there were also no significant differences in DM loss between the trees litters. They were found to be 45.65%, 48.15% and 41.73% for Hashab, Neem and Heiglig, respectively. After 8 weeks of decomposition, statistical analysis indicates that DM remained was not significantly different between litters. However, DM remained in Hashab (31.34%) seemed to be lower than that found in both Neem (42.04%) and Heiglig (41.52%). After 10 weeks, loss of DM from Hashab (72.38%) was also greater than observed in Neem (67.53%) and Heglig (57.1%). Therefore, despite of absence of significant difference, loss from Hashab was higher than that observed in Heglig and Neem by about 7 to 27%. After this period it was calculated that decomposition rate constants from Higlig, Hashab and Neem were 5.7, 6.8 and 7.3%, respectively. 55 Table 4.3. Actual changes of percent dry matter weight remaining of Heiglig (H), Neem(N) and Hashab (S) during the period of 10 weeks of decomposition. (Average ± standard deviations) Tree type Week2 Week4 Week6 Week8 Week1 0 (%) H N S 90.45a±3. 78.83a±5. 41.73a±5. 41.51a±11 42.94a±11 55 86 85 .22 .03 86.33a±10 75.08a±9. 48.15a±10 42.04a±17 32.47a±12 .85 38 .78 .13 .14 71.06b±12 71.90a±13 45.65a±5. 31.34a±6. 27.62a±12 .41 .78 86 13 .36 Values in columns followed by similar letter (s) were not significantly different at P ≤ 0.05 using Least Significant Difference (LSD) 56 4.2.2 Nutrient release: Percent Remaining N Nitrogen release during the incubation period (10 weeks) is shown in Table 4.4. Statistical analysis showed that, there was none significant difference in N remained in the second week among three trees litters. At the fourth week, statistical analysis indicates there is no significant difference for N released in trees litters, but the N remained in Heiglig, Neem and Hashab is lower by 13%, 12% and 5% respectively than N remained in second week. For 6th week, analysis showed that there was no significant difference among trees litters, however the N remained in this week in Heiglig, Neem and Hashab is lower by 16%, 21% and 8% respectively than in fourth week. At the 8th week, N remained in Heiglig was exceeded by 2% than the N remained in 6th week, while the N remained in both Neem and Hashab is lower by 5% than N remained in 6th week. Statistical analysis showed that, there was no significant difference among three tees litters by the end of 8th week. At 10th week, N remained in Heiglig, Neem and Hashab is lower by 1%, 10% and 6% respectively than the N remained in 8th week. Statistically no significant differences among the trees litters for N remained in 10th week. 57 Generally there was rapid loss N remained in both fourth and sixth week, from 6th week to 10th week no remarkable loss in N remained except the Neem in 10th week. Table 4.4. Actual changes of percent remaining N of Heiglig (H), Neem(N) and Hashab (S) during the period of 10 weeks of decomposition. (Average ± standard deviations) Tree Week2 Week4 N S Week8 Week10 (%) type H Week6 55.84a±12 42.14a±7. 26.5a±1.6 21.38a±6. 20.27a±7. .75 55 9 27 1 66.71a±19 54.66a±7. 33.27a±5. 28.48a±11 18.07a±8. .22 14 98 .70 74 47.24a±16 42.87a±19 34.38a±15 29.62a±14 23.36a±8. .78 .16 .04 .98 30 Values in columns followed by similar letter (s) were not significantly different at P ≤ 0.05 using Least Significant Difference (LSD) 4.2.2.2 Percent Remaining P Phosphorous release during the incubation period is shown in Table (4.5) After second week statistical analysis showed that there was no significant difference among trees litters for remained P. After the fourth week, analysis indicates there is no significant difference among the trees litters, 58 but there was a rapid loss in this week in both Heiglig (66.23% to 10.4%) and Neem (43.61% to 5.28%) than in Hashab (52.9% to22.01%). After sixth week, for P remained, statistical analysis showed that, there were no significant differences among the trees litters, but the P remained was exceeded among all trees litters than P remained in fourth week. For 8th week, the remained P was significantly lower in both Neem(3.61%) and Hashab(3.52%) than Heiglig(9.49%) at (p ≤ 0.04). At 10th week, analysis showed that, P remained in both Neem(2.83%) and Heiglig(5.19%) was significantly lower than P remained in Hashab(14.58%) at (p ≤ 0.01). In this week Hashab was exceeded by 38% than in 8th week . 59 Table 4.5 Actual changes of percent Phosphorus remaining of Heiglig(H), Neem(N) and Hashab(S) application during the period of 10 weeks of incubation Tree Week2 Week4 Week6 Week8 Week1 type 0 (%) H N S 60.23a±2 10.96a±2 39.40a±3 9.49a±4. 5.19b±3. 8.4 .3 2.1 5 6 43.61a±2 5.28b±2. 24.94a±1 3.61b±1. 2.83b±1. 9.5 3 4.5 2 3 52.94a±1 22.01a±2 29.14a±1 3.52b±1. 14.58a±4 8.2 1.4 8.6 5 ..6 Values in columns followed by similar letter (s) were not significantly different at P ≤ 0.05 using Least Significant Difference (LSD) 4.2.2.3 Remaining K: K release during the incubation period is shown in table (4.6). At second week statistical analysis indicates there is significant difference in K remained among the trees litters (p≤ 0.01), percentage remained K in Heiglig(32.97%) is lower than K remained in both Neem(55.76%) and 60 Hashab(68.54%). At fourth week, statistical analysis showed that, there were significant differences among trees litters (p ≤ 0.02), K remained in both Heiglig( 25.33%) and Neem(34.12%) is lower than in Hashab(56.46%). After the end of 6th week, statistical analysis showed that, K remained in both Heiglig(5.31%) and Neem(11,68%) was significantly lower than K remained in Hashab(31.28%) at (p ≤ 0.01). For the 8th week, statistical analysis showed that, there was significant difference among the three trees litters in K remained (p ≤ 0.01), Heiglig(3.53%) was the lowest followed by Neem(10.63%) and Hashab(20.72%) was the highest. At the end of 10th week, statistical analysis showed that, there were none significant differences among Heiglig(5.50%), Neem(3.87%) and Hashab(7.59%), but the K remained in this week was exceeded in Heiglig by 2% than K remained in 8th week. 61 Table 4.6 Actual changes of percent Potassium remaining of Heiglig(H), Neem(N) and Hashab(S) application during the period of 10 weeks of incubation. Tree Week2 Week4 Week6 Week8 Week1 type 0 (%) H N S 32.97b±6 25.35b±8 5.31b±1. 3.53b±1. 5.50a±2. .4 .4 7 6 3 55.76a±1 34.12b±1 11.68b±3 10.63b±4 3.87a±2. 7.6 5.4 .3 .7 6 68.54a±1 56.46±12 31.28±18 72a 20. 7.59a±4. 3.5 .1 .5 ±9.1 4 Values in columns followed by similar letter (s) were not significantly different at P ≤ 0.05 using Least Significant Difference (LSD) 4.2.3: ِAsh content Ash content during the incubation period (10week) is shown table (4.7). Statistical analysis showed that, Heiglig was significantly lower than both Neem and Hashab for ash content for all samples weeks (second week p ≤ 0.03, fourth week p ≤ 0.01, 6th week p ≤ 0.0001, 8th week p ≤ 0.0006 and 10th week p ≤ 0.0002). 62 Table 4.7 Actual changes of ash remaining of Heiglig(H), Neem(N) and Hashab(S) application during the period of 10 weeks of incubation. Tree Week2 Week4 Week6 Week8 type Week1 0 (g/kg) H 196.60b 187.63b 156.00b 124.58b 124.98b N 283.88a 263.10a 270.45a 241.10a 241.68a S 294.10a 274.68a 271.78a 2209.18a 227.80a Values in columns followed by similar letter (s) were not significantly different at P ≤ 0.05 using Least Significant Difference (LSD) . 63 CHAPTER FIVE Discussion 5.1. Cultivation of millet under different tree species 5.1.1. Effects on yield and straw dry matter In this study, millet cultivated under Heiglig and Neem trees were found to produce the highest dry matter yield and also dray matter of straw. This could possibly be due to their initial high N and K contents. However, the Hashab tree (though a legume tree) also contained similar amount of N but yields were lower than other tree species. It was reported earlier that initial N content of many leguminous plants were not good indicators of the N release. This is because other contents (for example lignin and polyphenols) might hasten release of the N. Palm (1995) showed that leguminous materials release nitrogen immediately, unless they contain high levels of lignin or polyphenols. Nonlegumes and litter of both legumes and nonlegumes generally immobilize N initially. Cannel et al. (1996) reported that agroforestry may increase production provided that the trees capture nutrients which are utilized by crops. Dry matter production and yield under Hashab trees are the lowest which could also be due to the low rate for the residues decomposition. The soil pH under the Hashab trees is the lowest, thus that may decreases microbial activities and decomposition of organic matter (Motavali et al., 1995) and also may cause imbalances in nutrients, especially major elements. However, Akbar et al. (1990) reported that the statistical analysis did not show any significant difference in the wheat yield among 64 different tree species (Eucalyptus camaldulensis, Albizia procera, Morus alba and Leucaena leucocephala) along the boundary of wheat fields. However, the wheat yield was numerically lowest at 2 m distance in case of all the four tree species and control. In case of mulberry, it was lowest statistically also from other distances. Numerically higher wheat yield values were noted at later distances (8, 10 and 12 m) in case of all tree species including control except for siris where numerically highest value was found at 6 m distance. Therefore, it can be generalized that tree's impact on wheat yield can be experienced up to 2 m distance, there is little, if any, impact up to 6 m distance and almost no impact at 8, 10 and 12 m distances. The results were also similar to Puri and Bangwara (1992) who studied he effect of Azadirachta indica, Prosopis cineraria, Dalbergia sissoo and Acacia nilotica on the yield of irrigated wheat crop. Their results indicate that A. indica and P. cineraria did not show any significant difference in the wheat yield while the other two species (D. sissoo and A. nilotica) showed a reduction in wheat yield. A. nilotica had the most significant and prominent effect, and a reduction of nearly 40 to 60% wheat yield was observed. The effect of this tree species was observed even beyond the spread of the crown. D. sissoo reduced yield by 4 to 30% but the reduction was only up to a distance of 3 m. In general, the impact of trees on wheat yield was observed up to 3 m distance and there is little, if any, impact up to 5 m distance and almost no impact at 7 m distance. In all the tree species, the wheat yield was reduced to a maximum on the north side of the trees and had almost no effect in the southern direction. Crop maturity was observed to be delayed by three weeks under A. nilotica, by 9–10 65 days under D. sissoo, and only by 6–7 days under P. cineraria and A. indica. 5.1.2. Effects on soil attributes After harvesting, for soil analysis results showed that, the pH under the Heiglig trees of the topsoil was higher than under other trees. This is possibly due to the much release of ash content from the leaves (see decomposition experiment). Ash content was reported to contain basic elements like Ca and Mg which may result in the increase in soil pH. Finzi et al. (1998) found that the pH under sugar marple (Acer saccharum) was significantly higher as compared to other trees. He found that exchangeable Ca and Mg were higher in that site. Moreover, the OC content under the Heiglig was significantly lower than that found under other trees. Therefore, it is expected that decomposition and release of organic acids will be low. These organic acids are responsible for the decrease in soil pH (Jekinson, 1981; Palm and Sanches, 1991; Porter et al., 1997). Gindaba et al. (2005) stated that Cordia macrostachyus and C. africana trees on farms keep soil nutrient high via protection against leaching, translocation of nutrients from deeper to the surface layer and accumulation of litter, which create a temporary nutrient pool in the surface soils under their canopies. This study found that the concentration of soluble salts tends to decrease in the presence of trees, especially under the Neem trees. It is expected these trees improves the aggregation of soil particles and hence this will improve leaching of accumulated cations. Shukla et al. (2006) studied the 66 soil quality under different trees and found that soil quality for each site was good and soil aggregation, water infiltration and SOC concentrations were high. However, the superiority of Neem over other trees might be due to better quality of organic acids which play an important role in the binding capacity of the soil particles. It is generally accepted that planting trees tend to increase soil OC. In this study, it was found that as a general trend, tree planting increased consistently soil OC. However, higher values of OC under the Hashab tree might possible indicates that decomposition of the C (which was not determined was slow). This is supported by the second experiment which showed that dry matter remained at the end of the decomposition period (Table 4.3) was the highest among the three species. This also means that litter quality did not decompose rapidly and tend to accumulate as C in the soil. The absence of significant difference in soil TN indicates that all tree species litters did not contribute significant amounts of N to the soil. This might be due to many factors, chief among them are biotic and abiotic factors. Despite the absence of significant difference between trees species in the contribution to soil P, which could be due to high C.V values, it was observed that in the 20-40 cm soil depth, there was higher amount of soil P under the Neem tree which might be due to higher initial P content (Table 3.2). Hagos and Smit (2005) reported similar results where they found that there were no statistical differences in soil K and P due to planting of various types of Acacia mellifera. This results also was 67 supported by Yadaf and Tarafdar (2004) who found that among trees phytase (an important enzyme in mobilizing P) activity was more under Neem trees Azadriachta indica. This study did not find any significant difference in soil K due different tree types. However, the K content in the 40-60 cm soil depth can not be miss-looked. This high amount of K in this depth which was found under the Neem trees was quite linked to the highest initial content as compared to Heiglig and Hashab. It could also be looked in different angle that K is one of the minerals that is easily leached from the cell since it is not bind to the cell components. Evidence exists that soil enrichment under tree canopies is a slow process. This is demonstrated by correlations between total C and N in soil under tree canopies and tree girth, an index of age (Bernhard-Reversat, 1982). This pattern of soil enrichment was also demonstrated by Belsky et al. (1989) in a semi-arid savanna in Kenya. The results of this study, with the highest nutrient status in soil close to the stem, thus support this observed soil enrichment pattern. The question of source and mechanism of soil enrichment under tree canopies remains largely unexplained. Many theories have been presented. Stemflow and throughfall represent a source of mineral input to soil (Williams et al., 1987; Potter, 1992). Leaf litter from leaf fall has also been mentioned as a possible source (Bosch and Van Wyk, 1970; Stuart-Hill et al., 1987; Belsky et al., 1989; Belsky, 1994). The total litter produced by savanna trees may consist of more than just leaves. The absence of quite clear effects of the Hashab tree, though it is a legume tree is consistent with Deans et al. (2003) who reported that there were few significant differences in soil fertility beneath the various Acacia sp. 68 Nevertheless, soil fertility beneath Azadriachta indica is more fertile than other N fixing trees. 5.2. Decomposition and nutrients release 5.2.1. Dry matter weight loss (DMW): The rapid initial mass loss in the second week in Hashab could be attributed to the removal of water soluble material by rainfall, this was supported earlier by Parsons et al. (1990). Mass loss in the early stages involved both physical leaching and microbial (Berg and Soaf, 1981; Berg and Wessen, 1984). A similar pattern of dry matter weight loss was observed in study of Ahlam (2004) on assessment of rate of decomposition and nutrient release from leaf residue of some trees species. 5.2.2. Nutrients release 5.2.2.1. Nitrogen For all tree litter types N was consistently and regularly released during incubation period, except the N remained in Heiglig at 8th week was increased from 19. 68% at 6th week to 21,38% at 8th week. This increase in N and followed by decline was earlier observed in mango and miombo leaves (Blair, 1988). Also Mtambanonywe and Kirchmann (1995) found similar result of N immobilization from litter of miombo followed by a net mineralization within 2 months. The increase in N concentration in decomposing litter is due to mechanisms such as, microbial immobilization of N (Koeing and Cochran, 1994), fungal translocation, through fall and insect frass (Melillo et al., 1982). 69 5.2.2.2. Phosphorous Phosphours release pattern from all tree litter types seemed to be erratic and did not follow a consistent norm. The rapid loss of P observed here after the end of the fourth week was probably due to removal of soluble P by excessive rainfall. Many studies found that P can be leached in the early stages of decomposition (Musvoto et al., 1999; and Tiquia et al., 2002). However the increase of P leaching reported here at the last stages of decomposition period which synchronized with the beginning of the rainy season. This was also observed by other studies (Blair, 1988; Tripathi and Singh, 1992). The increase of P content observed at the sixth week (in three tree residue) indicates that P could be a limiting nutrient for decomposers. Many studies showed accumulation of P as well as N during decomposition (Staaf and Berg 1982; O,Cnnel 1988). In some cases, P accumulates faster than N during decay of forest debris (Lambert et al; 1980) indicating that the dependence of decomposer activity for phosphours. Other study by O, Cnnel, (2004) showed that there was four, fold increase in the amount of P in mesh bags after decomposition for 5years. Thus, the input of P from lower strata in the litter and mineral soil, probably through translocation in the hyphae of soil and litter fungi (Gholz et al., 1985). 5.2.2.3. Potassium In the second, fourth, six and eighth week of decomposition it was observed that, the Heiglig released K faster than Neem and Hashab, but at the 10th and last week of incubation period, the release of K seemed to be 70 steady and slower in Heiglig and faster in both Hashab and Neem . The high potential for K leaching from plant residues in the early stage of this study is consistent with study showing significant relationships between plant quality indices and K release as suggested by Tian et al; (1992). The high loss of initial K observed here was also reported earlier (Cobo 2002; Laskowsk; and Berg 1993; Singh and Shekhar, 1989). Because K is not a structural element, it is susceptible to high initial loss by leaching, as also reported by Staaf (1980). Others studies also reported that, K release were not to be affected by chemical composition because this cation is not incorporated into the organic compounds tissue in the plant so it is easily leached from residues (Jung et al., 1968; Bunnel and Tiat 1974; Berg 1984; Saini 1989; Reddy and Venkataiah 1989). The slow release of K observed here might be due to the little change in soil exchangeable cation contents, supported by the studies of (Lupway; and Haque, 1998 Alam, 2004). 71 CHAPTER SIX Conclusions and Recommendations 6.1: Conclusions: 1 This study showed that, millet production grown with Neem and Heiglig trees recorded highest dry matter both straw and yield. 2 Trees vary in their capacity to induce changes in soil pH, OC, ECe and effects on soil K, P and N were not substantial. In this respect, the Hashab tree was found to contribute much higher amounts of SOC to the soil. However, due to high initial content, Neem tree could be a good source for enriching soil with P. 3 Heiglig litter is a good source for K, due to the rapid loss of K during the incubation period of decomposition. 4 An important aspect, Phosphorus and N release patterns from all tree litters studies, did not show a period of immobilization indicated by a concentration that was higher than the initial content (100%). This result indicates that incorporation of such litters do not seem to cause P or N starvation to accompanied annual crops. 72 6.2: Recommendations: 1.If the main aim is to increase and sustain crops production in sandy soil, it is worth to utilize the capacity of trees in the improvement of soil fertility. 2.For long term fertility correction (ie. Build up of soil organic matter), combined mulch from Neem and Heiglig or application of litter from Hashab could improve content of soil organic carbon. 3.Judicious application of mixed Heiglig or Neem with Hashab will improve both short and long term soil fertility improvement. 4.Litter from Hashab decomposed slowly. This phenomenon increases chances of accumulation of soil organic matter; hence, this tree might be useful in moisture conservation in such soils. Consequently, it is expected that the soil under such tree will be of better resilience which is important in the reduction of soil erosion. 5. It is suggested that further studies should look into (1) biological effects (e.g. microbial biomass C and N, soil enzymes) and (2) soil stability indices. 73 References Adrien C. Finzi, Charles D. Canham and Nico van Breemen. (1998). Canopy Tree-Soil Interactions within Temperate Forests: Species Effects on pH and Cations Ecological Applications, Vol. 8, No. 2: 447-454 Aerts, R., Verhoeven, J.T.A., and Whigham, D.F. (1999). Plantmediated controls on nutrient cycling in temperate fens and bogs. Ecology, 80: 2170– 2181. Ahlam, A.M. (2004). Assessment of rate of decomposition and nutrient release from leaf residue of some tree species. M.Sc. Thesis desertification, U. of K. Akbar G., Ahmed, M., Rafique, S., and K.N. Babar. (1990). Effect of trees on the yiled of wheat crop. Agroforestry systems 11: 1-10. Amelung, W. (2001). Methods using amino sugars as markers for microbial residues in soil. In Assessment Methods for Soil Carbon. R. Lal, J.M. Kimble, R.F. Follett and B.A. Stewart (eds). CRC/Lewis Publishers,Boca Raton, FL, pp. 233 – 267. Andrews. Fw(1950- 1956): The flowing plants of the anglo . Egyption Sudan, published for the Sudan Government by T Bunkle and co. ltd, Arboath, UK. Apdein Mohamed Abdalla (1990-91). Personal communications (Assistant Manager. ELAin NFMP, Sudan). ASB (Alternatives to Slash and Burn research consortium). Undated. Alternatives to slash and burn: A global initiative. Nairobi, ICRAF. Balser, T.C. (2005) Humifi cation. In Encyclopedia of Soils in the Environment. D. Hillel et al. (eds). Vol. 2. Elsevier, Oxford, UK, pp. 195 – 207. Bardgett, R.D. and McAlister, E. (1999). The measurement of soil fungal: 74 bacterial biomass ratios as an indicator of ecosystem self-regulation in temperate meadow grasslands. Biol. Fertil. Soils 29 , 282 – 290. Bardgett, R.D. and Walker, L.R. (2004) Impact of colonizer plant species on the development of decomposer microbial communities following deglaciation. Soil Biol. Biochem. 36 , 555 – 559. Barth, R.C. & Klemmedson, J.O. (1982). Amount and distribution of dry matter, nitrogen and organic carbon in soil-plant systems of mesquite and palo verde. Journal of Range Management, 35: 412–418. Basher, I.H. (2003). Producing and marketing Arabic in Dilling area partial fuel fillment research for B. Sc. Dilling university, Dilling. Bauhus, J., Paré, D. and Côté, L. (1998). Effects of tree species, stand age and soil type on soil microbial biomass and its activity in a southern boreal forest. Soil Biol. Biochem. 30 , 1077 – 1089 Belsky, A.J., Mwonga, S.M., Amundson, R.G., Duxbury, J.M. & Ali, A.R. - (1993). Comparative effects of isolated trees on their under canopy environments in high- and low-rainfall savannas. Journal of Applied Ecology, 30: 143–155. Belyea, L.R. (1996). Separating the effects of litter quality and microenvironment on decomposition rates in a patterned peatland. Oikos, 77: 529–539. Berg, B. (1984). Decomposition of root litter and some factors regulating the process: Long-term root litter decomposition in Scots pine forest. Soil Biology and Biochemistry 16: 609-617. Berg, B. and Staaf, H. (1981). Leaching accumulation and release of nitrogen in decomposing forest litter. Ecol. Bull.33:163-178. Berg, B. and Wessen, B. (1984). Changes in organic chemical components and in growth of fungal mycelium in decomposing birch leaf litter as 75 compared to pine needles. Pedobiological 26: 285-298. Blair, G.J.; Blair, N.; Lefroy, R.D.B.; Conteh, A. and Daniel, H. (1997). Relationships between KMnO2 oxidizable C and soil aggregate stability and the derivation of carbon management index. In: The role of humic substances in the ecosystems and environmental protection (Eds J. Drozd, SS Gonet. N Sensi. J Weber) pp. 227-232. Blume , H., P. (1965). Die Charakterisierung von Humuskorpern durch Streu-und Humns – Stoffgrup – penanalysen unter Berucksichtigung ihrer morphologischen Eigenschaften . Z. PflanzenernaehrDueng . Bodenkd . 111 : 95 – 114. Branney.P (1989). "propagation of tree species for afforestation in Northern Sudan". Find report for ODA. Bravard, S. Righi, D., (1991). Characterization of fulvic and humic acids from an Oxisol-Spodosol toposequence of Amazonia, Brazil. Geoderma 48, 151-162. Brethelin, J., and F. Toutain. (1982). Soil Biology . In Constituents and Prosperities of soil . M . Bonneau and B . Souchier (eds) . Academic Press, London , pp. 140 – 183. Bridgham, S.D., Updegraff, K., and Pastor, J. (1998). Carbon, nitrogen and phosphorus mineralization in northern wetlands. Ecology, 79: 1545– 1561. Brookes P.C. (1995). The use of microbial parameters in monitoring soil pollution by heavy metals. Biology and Fertility of Soils 19, 269–279. Bunnell, F.L. and Tait, D.E. (1974). Mathematical simulation models of decomposition in Tundra, A.J. Holding, O.W. Heal, S.F. Maclean and P.W. Flanagan (Eds), pp. 207-226. Swedish IBP Committee, Stockholm. Campbell, C., Vitt, D.H., Halsey, L.A., Campbell, I.D., Thormann, 76 M.N., and Bayley, S.E. (2000). Net primary production and standing standing biomass in northern continental wetlands. Can. For. Serv. Inf. Rep. NOR-X-369. Cannell, M.G.R., van Noordwijk, M., Ong, C.K., (1996). The central agroforestry hypothesis: the tree must acquire resources that the crop would not otherwise acquire . Agrofor. Syst.34, 27-31. Champan, H.D and part, P.F. (1961). Methods of analysis of soil, plant waters University of California USA. Chantigny, M.H., Angers, D.A., Prévost, D., Vézina, L.P. and Chalifour, F.-P. (1997). Soil aggregation and fungal and bacterial biomass under annual and perennial cropping systems. Soil Sci.Soc. Am. J.61,262– 267. Clymo, R.S. (1965). Experiments on the breakdown of Sphagnum in two bogs. J. Ecol. 53: 747–757. Cobo, J.G.; Barrios, Kass, D.C.L. and Thomas, R.J. (2002). Decomposition and nutrient release by green manures in a tropical hillside agroecosystem. Plant and soil 240: 331342. Day, F.P. (1983). Effects of flooding on leaf litter decomposition in microcosms. Oecologia, 56: 180–184. Deans et al. (2003). Forest ecology and management. Vol 176: 253-264. Deans, J. D., Lindley, D.K., Munro, R., C., (1995). Deep Beneath Trees in Senegal. Annual report 1993, Institute of Terrestrial Ecology, Bush Estate, penicuik, Scotland, UK, 1994, pp. 12-14. Doran J.W. & Parkin T.B. (1994). Defining and assessing soil quality. In: Defining soil quality for a sustainable environment, ed JW Doran, SSSA Special Publication no. 35. SSSA ASA Madison WI pp 3–21. Dubois, O. (2003). Forest-Based Poverty Reduction: A Brief Review of Facts, Figures, Challenges and Possible Ways Forward. Pp. 65-83. In: Oksanen, Pajari, Tuomasjukka (eds.) Forests in Poverty Reduction 77 Strategies: Capturing the Potential. EFI Proceedings No. 47. European Forest Institute. 206 p. Duchafour , P. (1976). Dynamics of Organic matter in Soils of temperature regions : Its action on pedogenesis . Geoderma 15:31 – 40 . Edmunds, W.M., (1991). Ground-water Recharge in the West African Sahel. Natural Environmental Research Council News No.17,pp.8-10. Frolking, S., Roulet, N.T., Moore, T.R., Richard, P.J.H., Lavoie, M., and Muller, S.D. (2001). Modelling northern peatland decomposition and peat accumulation. Ecosystems, 4: 479–498. G.B. (1982). Seasonal dynamics of nitrogen cycling for a Prosopis woodland in the Sonoran Loftis, S.G. & Kurtz, E.B. (1980). Field studies of inorganic nitrogen added to semi - arid soils by rainfall and blue-green algae. Soil Science, 129: 150–155. Garcia-Moya, E., & McKell, C.M. (1970). Contribution of shrubs to the nitrogen economy of a desert wash plant community. Ecology, 51: 81–88. Gholz, I.I.L.; Perry, C.S.; Cropper, W.P. and Hendry, L.C. (1985). Litterfall, decomposition, and nitrogen and phosphorus dynamics in a chronoseuence of slash pine (Pinus elliottii) plantation. For Sci. 31: 463478. Glaser, B., Turriَn, M.-B. and Alef, K. (2004) Amino sugars and muramic acid – biomarkers for soil microbial community structure analysis. Soil Biol. Biochem. 36 , 399 – 407. Glover, E.K. 2005. Tropical dryland rehabilitation Case study on participatory forest management in Gedaref, Sudan. Doctoral thesis. University of Helsinki, Dept. of Forest Ecology, Viikki Tropical Resources Institute (VITRI). 183 p. Grayston, S.J. and Prescott, C.E. (2005). Microbial communities in forest 78 floors under four tree species in coastal British Columbia. Soil Biol. Biochem. 37 , 1157 – 1167. Grayston, S.J., Griffi th, G.S., Mawdsley, J.L., Campbell, C.D. and Bardgett, R.D. (2001) Accounting for variability in soil microbial communities of temperate upland grassland ecosystems. Soil Biol. Biochem. 33 , 533 – 551. Guggenberger, G., Frey, S.D., Six, J., Paustian, K. and Elliott, E.T. (1999). Bacterial and fungal cell-wall residues in conventional and notillage agroecosystems. Soil Sci. Soc. Am. J. 63 , 1188 – 1198. Hackl, E., Pfeffer, M., Donat, C., Bachmann, G. and ZechmeisterBoltenstern, S. (2005). Composition of the microbial communities in the mineral soil under different types of natural forest. Soil Biol. Biochem. 37, 661 – 671. Hamza Mohamed ELAmin (1990). Trees and shrubs of the Sudan, Ithaca press, Exeter, UK. Haque I., powell, J. M. and Ehui, S. (1995). Improved crop-livestock production strategies for sustainable soil management in tropical Africa. In soil Management: Experamental Basis for sustainability and Environmental Quality, Advances in Soil Science, ed. R. Lal and B.A. Stewart, pp. 293345. Lewis, Boca Raton. Hellin, J. 2006. Better Land Husbandry: From Soil Conservation to Holistic Land Management. Science Publishers, Enfield and Plymouth. 325 p. Hogg, E.H., Malmer, N., and Wallen, B. (1994). Microsite and regional variation in the potential decay-rate of Sphagnum-magellanicum in south Swedish raised bogs. Ecography, 17: 50–59. Hornik S. B. (1992). Factors affecting the nutritional quality of crops. American Journal of Alternative Agriculture 7, 63–68. 79 Jenkinson, D.S. (1981). The fate of plant and animal residues in soil. In the Chemistry of Soil Pro Processes. Eds. D.J. Green land and M.H.B. Hayes. Pp. 505-561. John Wiley and Sons, New York. Jenny, H. (1944). Factors of soil formation. New York: McGraw-Hill Book Co., 281 pp. undel, P.W., Nilsen, E.T., Sharifi, M.R., Virginia, R.A., Jarrell, W.M., Kohl, D.H. & Shearer. Jiregna Gindaba . Andrey Rozanov . Legesse Negash (2005). Trees on farms and their contribution to soil fertility parameters in Badessa, eastern Ethiopia. Plant and Soil 42: 66-71. Johnson, H.B. & Mayeux, H.S. (1990). Prosopis glandulosa and the nitrogen balance of rangelands: Extent and occurrence of nodulation. Oecologia, 84: 176–185. Johnson, L.C., and Damman, A.W.H. (1991). Species controlled Sphagnum decay on a south Swedish raised bog. Oikos, 61: 234–242. June, G.; Bruckert, S. and Dommergues, Y. (1968). Etude compare de diverses substances hydrosolubles extraites de quelques litters tropicals et temperees. Oecologia plantarum 3: 237-253. Kandeler E. Tscherko D. & Spiegel H. (1999). Long-term monitoring of microbial biomass, N mineralization and enzyme activities of a chernozem under different tillage management. Biology and Fertility of Soils 28, 343– 351. Kang B. T., Reynolds, L. and Atta-Krah, A. N. (1990). Alley farming. Advances in Agronomy 43,315-359. Kerkhof, P. (1988). Agroforestry Manual for taita, taveta District, Kenya forest Dept/ DAN/ A/ Kenya Kidd,C.V.,Pimental,D.,(1992). Integrated Resource Management: Agroforestry for Development. Academic press, San Diego,USA. 80 L. sindicus root rhizosphere has higher phytase activity. Lal, R., (2001). The potential of soil carbon sequestration in forest ecosystems to mitigate the greenhouse effect. Soil Science Society of America, Special publication No. 57, pp.137-154. Lambert, R.L.; Lang, G.E. and Reiners, W.A. (1980). Loss of mass and chemical change in decaying boles of a subalpine balsam fir forest. Ecology 61: 1460-1473. Laskowski, R. and Berg, B. (1993). Dynamics of some mineral nutrients and heavy metals in decomposing forest litter. Scand J. For Res. 8: 446456. Lima, W.P.(1996). Impacto ambiental do eucalipto. Sao Paulo Edusp., 301pp. Lockaby, B.G., Wheat, R.S., and Clawson, R.G. (1996). Influence of hydroperiod on litter conversion to soil organic matter in a floodplain forest. Soil Sci. Soc. Am. J. 60: 1989–1993. Lupwayi, N.Z. and Haque, I. (1999). Leucaena hedgerow intercropping and cattle manure application in the Ethiopian high lands I. Decomposition and nutrient release. Biology and Fertility of Soils 28, pp 128-195. M.G. Hagos, G.N. Smit. (2005). Soil enrichment by Acacia mellifera subsp. detinens on nutrient poor sandy soil in a semi-arid southern African savanna. Journal of Arid Environments 61 (2005) 47–59 M.K. Shukla, R. Lal, M. Ebinger, C. Meyer. 2006. Physical and chemical properties of soils under some pin˜ on-juniper-oak canopies in a semi-arid ecosystem in New Mexico. Journal of Arid Environments 66 (2006) 673– 685. Mack Dicken.K.G, and N.T.Vergara. (1990). Introduction to agroforetry. In Mack --..Dicken, K.G. and N.T. Vergara(eds.). 1990 Agroforestry classification and management. John willey and Sons, Inc, NewYorks. pp. 81 1- 30. Mahony, D. (1990). Tree of Somalia: a filed guide for Development workers, OXFAM, oxford, UK . Mangenot , F., and F . Toutain . (1980) . Les litieres . In Actualities d’ecologie forestiere : Sol , flore , faune , P. Pesson (ed) . Gauthier – Villars , Paris , pp. 3-59 . Meentemeyer, V. (1995). Meteorologic control of liter decomposition: With an emphasis on tropical environments. In: Reddy MV (ed) Soil Organisms and Litter Decomposition in the Tropics, pp 153-182. Oxford & IBH, New Delhi, India. Mendonca, E.S., Rowell, D.L., (1996). Mineral and organic fraction of two Oxisols and their influence on effective cation-exchange capacity. Soul Sci. Am. J. 60, 1888-1892. Moore, T.R., Bubier J.L., Frolking, S.E., Lafleur, P.M., and Roulet, N.T. (2002). Plant biomass and production and CO2 exchange in an ombrotrophic bog. J. Ecol. 90: 25–36. Motavalli, P.P.; Plam, C.A.; Parton, W.J.; Elliott, E.T. and Frey, S.D. (1995a). Soil pH and organic C dynamics in tropical forest soils: Evidence from laboratory and simulation studies. Soil boil. Biochem. 27: 1589-1599. Myers R. J.K., palm,C.A., Cuevas,E., Gunatilleke, I.U.N. and Brossard,M. (1994). The synchronization of nutrient mineralization and plant nutrient demand. In: Woolmer PL and Swift M.J(eds). The biological Management of tropical Soil Fertility,.pp 81-116. John Wiley and Sons,Chichester, UK. Myers, R.T., Zak, D.R., White, D.C. and Peacock, A. (2001) Landscapelevel patterns of microbial community composition and substrate use in upland forest ecosystems. Soil Sci. Soc. Am. J. 65, 359 – 367. 82 Nannipieri, P., Pedrazzini, F., Arcara, PG. and Piovanelli, C. (1979) Changes in amino acids, enzyme activities, and biomasses during soil microbial growth. Soil Sci. 127 , 26 – 34. Nascimeto, V.M., Almendros, G., Fernandes, F.M., (1992). Soil humus characterization in virgin and cleared areas of the Parana River basin in Brazil. Geoderma 54, 137-150. National Academy of sciences (1980): fire wood crops vol.2. shrub and tree species for energy production, National Academy of sciences, Washington. D.C. USA . Nkonya, E., Pender, J., Jagger, P., Sserunkuuma, D., Kaizzi, C. and Ssali, H. 2004. Strategies for sustainable land management and poverty reduction in Uganda. Research Report 133. International Food Policy Research Institute. Washington D.C. 136 p. O'Connell, A.M.; Grove, T.S.; Mendham, D. and Rance, S.J. (2000). Effects of site management in eucalypt plantations in south western Australia. In: Nambiar EKS, Tiarks, A., Cossalter C Ranger J (eds) site management and productivity in tropical plantation forest. CIFOR, Bogor, Indonesia, pp. 61-71. Olsen, S.R.; Cole, C.V. (1954). Estimation of available phosphours in soils by extraction with sodium bicarbonate. W.S. Department. Agric. Circular NO. 393. Ong,C.K.,Odongo,J.C.W.,Marshall,F.,Black,C.R.,(1992).Wate use of agroforestry systems R.L.,Adlard,P.G.(Eds.), in semi Growth arid and India.In:Calder,I.R., Water Use of Hall, Plantations. Wiley,Chichester,pp.347-358. Painter, T.J. (1991). Lindow Man, Tollund Man and other peat-bog bodies: the preservative and antimicrobial action of Sphanan, a reactive glycurnoglycan with tanning and sequestering properties. Carbohydr. 83 Polym. 15: 123–142. Palm C. A. (1995). Contribution of agroforestry trees to nutrient requirements of intercropped plants. Agroforestry Systems 30: 105-124 Palm, C.A. (1995). Contribution of agroforestry trees to nutrient requirements of inter-cropped plants. Agroforestry Systems 30: 105-124. Palm, C.A. and Sanchez, P.A. (1991). Nitrogen release from the leaves of some tropical legumes as affected by their lignin and polyphenolic contents. Soil Biology & Biochemistry 23: 83-88. Parsons, J.W. (1981) Chemistry and distribution of amino sugars. In Soil Biochemistry. E.A. Paul and J.N. Ladd (eds). Vol. 5. Marcel Dekker Inc., New York, pp. 197 – 227. Parsons, W.F.J.; Taylor, B.R. and Parkinson, D. (1990). Decomposition of aspen (Populus tremuloides) leaf litter modified by leaching. Can. J. Forest Res. 20: 943-951. Paulas, IR and Abdein Mohamed Abdalla (1990). Gum Arabic Manual (sud/ 84/x01) united National Sudan. Sahelian office, New York, USA . Potila, H., Sarjala, T. and Aro, L. (2004) Does dominant tree species affect soil microbial community in cut-away peatland? In Wise Use of Peatlands. Proceedings of the 12th International Peat Congress. J. Priha, O., Grayston, S.J., Hiukka, R., Pennanen, T. and Smolander, A. (2001) Microbial community structure and characteristics of the organic matter in soils under Pinus sylvestris, Picea abies and Betula pendula seedlings at two forest sites. Biol Fertil. Soils 33 , 17 – 24. Puri S. and Bangarwa.K. S. (1992). Effects of trees on the yield irrigated wheat crop in semi-arid regions. Agroforestry Systems 20: 229-241. Rain tree, J. B. (1987). Dand Dusers manual: An introduction to agroforestry dianosis and design. International council for research in 84 Agroforestry, Nairobi, Kenya . Reddy, V.M. and Venkataiah, B. (1989). Influence of micro-arthropod abundance and limatic factors on weight loss and mineral nutrient contents of eucalyptus leaf litter during decomposition. Biology and fertility of soils, 8: 319-324. Resck, D.V.S., Vasconcellos, C.A., Vilela, L., Macedo, M.C.M., (2000). Impact of conversion of Brazilian Cerralos to cropland and pastureland on soil carbon pool and dynamics. In: Lal, R., Kimble, J.M., Stewart, B.A. (Eds.), Global Climate Change and Tropical Ecosystems. CRC/Lewis Press, Boca Raton, pp.169-196. Rochefort, L., Vitt, D.H., and Bayley, S.E. (1990). Growth, production and decomposition dynamics of Sphagnum under natural and experimentally acidified conditions. Ecology, 71: 1986–2000. Rockstorm,J.,(1997). On-farm agrohydrological analysis of the Sahelian yield crisis: rainfall partitioning, soil nutrients and water use efficiency of pearl miller. Ph. D. Thesis, University of Stockholm, UK. Sah, S. (1996). Use of farmers’ knowledge to forecast areas of cardamom cultivation. An application of a participatory land suitability analysis in East Usambaras, Tanzania. ITC. 161 p. Saini, R.C. (1989). Mass loss and nitrogen concentration changes during the decomposition of rice residues under field conditions. Pedobilogia, 33: 235299. Salih , F.A.(2003). Effect of armed conflicts on the population demography in Dilling province, M. Sc. Thesis Nilain university, Khartoum. Sanchez, P.A., Buresh, R.J. and Leakey, R.R.B. (1997). Trees, soils, and food security. Biological Transactions of the Royal Society 352: 949-961. London, Great Britain. 85 SAS (1985). SAS User's Guide: Statistics, 5th ed., SAS Institute, Cary, N.C. Scanlon, D., and Moore, T.R. (2000). CO2 production from peatland soil profiles: the influence of temperature, oxic/anoxic conditions and substrate. Soil Sci. 165: 153–160. Scherr, S. 1999. Soil Degradation: a threat to developing-country food security by 2020? Food, Agriculture and the Environment Discussion Paper 27. International Food Policy Research Institute. Washington D.C. 63 p. Silva, J.E., Lemainski, J., Resck, D.V.S., (1994) Perdas de materia organica e suas relacoes com a capacidade de troca cationica em solos da regiao de Cerados do oest baiano. Rev. Bras. Cienc.Solo 18, 541-547. Snyder , K . E ., and S. A . L . Pilgrim . 1985 , Sharper Focus on forest floor horizons . Soil Surv . Horizons 26:9-15 . Staaf, H. (1980). Release of plant nutrients from decomposing leaf litter in a South Swedish beech forest. Holarct Ecol. 3: 129-136 Staaf, H. and Berg, B. (1982). Accumulation and release of plant nutrients in decomposing Scots pine needle litter. Long-term decomposition in a Scots pine forest II. Can. J. Bot. 60: 1561-1568. Swift , M . J ., O . W . Heal , and J. M . Anderson , 1979 Decomposition in terrestrial ecosystems . Blackwell , Oxford. Swift, M.J. (1985). Tropical soil biology and fertility: Planning for rsearch. Biology International Special issue 9.24p. Szumigalski, A.R., and Bayley, S.E. (1996). Decomposition along a bog– fen gradient in central Alberta. Can. J. Bot. 74: 573–581. Thirakul, s(1984):M annual of Dendrology Canadian International Development Agency(CIDA) forest invevtory and market demand survey project, Bahr elghazal and Central Regions. Democratic Republic of the Sudan. 86 Thormann, M.N., and Bayley, S.E. (1997). Decomposition along a moderate-rich fen-marsh peatland gradient in boreal Alberta, Canada. Wetlands, 17: 123–137. Tian, G.; Kang, B.T. and Brussaard, L. (1992a). Effects of chemical composition on N, Ca and mg release during incubation of leaves from selected agro-forestry and fallow species. Biogeochemistry 5: 1-17. Trasar C.C. Leiros C. Gil S.F. & Seoane S. (1998). Towards a biochemical quality index for soils: An expression relating several biological and biochemical properties. Biology and Fertility of Soils 26, 100–106. Tripathi S.K. and Singh, K.P. (1992). Nutrient immobilization and release patterns during plant decomposition in a dry tropical bamboo savanna. India. Biology and Fertility of Soils, 14: 191-199. Turner, D.P., Sollins, P., Leuking, M. and Rudd, N. (1993). Availability and uptake of inorganic nitrogen in a mixed old-growth coniferous forest. Plant Soil. 148 , 163 – 174. UNDP. 1995. Agroecology: Creating the Synergism for a Sustainable Agriculture. UNDP Guidebook Series.87 p. Van Breemen, N. (1995). How Sphagnum bogs down other plants. Trends Ecol. Evol. 10: 270–275. Vergara N.T (1983). Agroforestry systems: Aprimer. Unasylva 37. 32. 28 . Vogt. K. (1987): Apreliminary Report on Results obtained in aseries of species trails, Turkana, Kenga. Volkoff, B., Polo, A., Cerri, C.C., (1988). Caracteristiques biochimiques des acides humiques des sols tropicaux du Bresil. Distintion Fonamentale entre les sols equatoriaux et les sols des regions a climat tropical contraste Comptes Rendus Acad. Sci. Paris 307, 95-100. 87 Von Maydell, H.I(1986): trees and shrubs of the Sahel, Their characteristics and uses,GTZ Nerlag Josef Margraf, weikersheim, Germany. Waksman , S . A ., and F. G . Tenney . 1927 . The composition of natural organic material and their decomposition in the soil : 1. methods of quantitative analysis of plant materials . Soil Sci . 24 : 317- 333. White,D.A.,Dunin,F.X.,Turner,N.C.,Ward,B.H.,Galbraith,J.H.,(2002). Water use by contour-planted belts of trees comprised of four Eucalyptus species. Agric. Water Manage.53,133-152. Wickens, G.E. (1990- 95). Personal communications . Wickens. G.E (1980). "Alternative uses of browse species" in Browse in Africa, Le. Houerou, ILCA, Addis Ababa, Ethiopia . Yadav, B.K., J.C. Tarafdar. (2004). Phytase activity in the rhizosphere of crops, trees and grasses under arid environment. Journal of Arid Environments 58 (2004) 285–293. Young, A. (1983), An environmental data base for agroforestry . ICRAF working paper 5, Nairobi, Kenya. Young, A., (2000). How much spare land exists? Bull. Int. Union Soil Sci., in press. Zinn, Y.L.,(1998). Caracteuzacao de propriedades fisicas, qumicas e da materia organica de solos nos Cerrados sob plantacoes de Eucalyptus e Pinus. M.Sc. thesis, Univesity of Brasilia, 85 pp. unpublished. 88
© Copyright 2024