Nutrient Cycles and Integrated Soil Fertility Management in Geba Catchment, Northern Ethiopia
Nutriëntencycli en geïntegreerd bodemvruchtbaarheidbeheer in het Geba bekken van het bergland in Noord Ethiopië
Woldetensai, Gebreyohannes Girmay; S0186028
English Summary Ethiopia has been facing serious food shortages as food production growth has not kept pace with population growth. The rugged topography and steep slopes, removal of vegetation cover and high rainfall erosivity makes agricultural land prone to erosion. Loss of soil organic matter and nutrients due to removal of the vegetation cover through long term practices of overcultivation and overgrazing are primary causes for soil fertility decline that resulted in low agricultural productivity. The Ethiopian highland soils are deficient in nutrients such as total nitrogen, available phosphorus, iron and zinc. Agricultural production demands for replenishment of the soil fertility. The prevailing predictions made on nutrient losses at national level so far are coarse to be used as information for deciding on precise soil fertility management options at local level. Hence, it is imperative to systematically establish field scale nutrient balance assessment experiments in order to obtain reliable information for planning, implementing and monitoring integrated soil fertility management projects adapted to specific conditions at local level. Thus, the objectives of this research were: · To increase the productivity levels of crops such as wheat through application of N and P fertilizers on specific soil type under rainfed conditions in order to indicate efficient ways to meet the ever-increasing food demand and to achieve household food securityTo understand the significance of N-fixation by legumes in response to applied P and Zn fertilizers on calcareous soils leading to increased yield of subsequent cereal crops such as wheat in the crop rotation systemsTo evaluate the potential of reservoir sediments through studying their fertility characteristics for reclaiming bare land and for subsequent crop production on reclaimed bare landsTo understand and discuss nutrient flow pathways at farm level and main causes of soil nutrient depletion in perspective of the role of household wealth and landscape positions in micro-catchments and recommend strategies for improving nutrient management and crop productivity in the existing farming systems· To understand the causes for and the variability of runoff associated nutrient flows and suggest alternative tools and techniques for management of runoff nutrients for improving in-situ soil fertility and crop performance in the micro-catchments· To understand the variations in release and flow patterns of materials and nutrients in the different landscapes and socio-economic conditions and investigate the implications on maintenance of the nutrient balance in the northern Ethiopian highlands This study shows that a substantial increase in food production can be achieved from using mineral fertilizers in crop lands of declining soil fertility. Increased application rates of mineral fertilizers can build up the nutrient status of the soils thereby improving their responsiveness to inputs and increasing crop productivity in a sustainable way. Furthermore, fertilizer application such as P and Zn to grain legumes grown on less fertile soils improves the grain yield and N2 fixation by the legumes. Furthermore, reclamation of bare lands using reservoir sediments, subsequent growing of garlic resulted in a three-fold increase in bulb yield (from 2.0 to 7.7 t/ha) when bare lands were reclaimed using a 15-cm layer of reservoir sediment.In order to provide farming communities an opportunity to judiciously manage their soil nutrient resources, monitoring nutrient flows can be a vital tool to understand sustainability of the subsistence farming systems and to precisely identify and quantify the nutrient gains and losses of a given farm. Our study along this line also showed a negative nutrient balance at farm scale for N (54 kg/ha.yr) and K (16 kg/ha.yr). Furthermore, it was found there is diversity of the crop nutrient import-export patterns among various household wealth groups, namely; poor, medium and rich households. We found that specific nutrient movement patterns can be defined for various landscape positions and socio-economic groups and understanding these patterns would enable planning and implementing improved soil fertility management through properly harvesting runoff associated nutrients. Soil fertility depletion in smallholder farms is often related to ownership and access to productive assets and their careful management by the households. The resource rich farmers own large livestock with sufficient draught power, cultivate more land, produce more manure, purchase more fertilizer and generate large production output. The significant variation in resource endowment of households in turn has a major impact on farmers success in agricultural activity and soil fertility management. This calls for household variable packages of soil fertility management at farm scale. Higher nutrient mining rate is primarily due to large removals of nutrients in harvested crops and crop residues. Development of other feed sources such as cut and carry systems from exclosures should receive priority. The holistic approach designed for and employed to achieve the objectives of this research can be used as a valid methodological approach to undertake research and development projects for areas in a comparable agro-ecological setting as the northern Ethiopian highlands.