Abstract

Soil fertility depletion in smallholder farms is one of the fundamental biophysical causes for declining use per capita food production in Ethiopia. In the present study, resource flow analysis was made at catchment scale in northern Ethiopia, analyzing nutrient balances. JMP 5, a computer program for statistics and used in applications such as design experiment and scientific research was used to process and to analyze the data of different resources flow into and out of the watershed. Nutrient balances for N, P and K from four nutrient fluxes entering and four nutrient fluxes leaving the watershed were calculated. Some of the fluxes (e.g. wet deposition and gaseous losses) were estimated using transfer functions. At the catchment level, full nutrient balance results indicate a depletion rate of  -42.5 to 13.1 kg N ha^-1year^-1 (for the rich) and -32.7 kg N ha^-1 year^-1, -11.8 kg K ha^-1year^-1 (for the medium) in the upper landscape, -49 kg N ha^-1 year^-1, -14.3 kg K ha^-1 year^-1 ( for  the rich) and -28.5 kg N ha^-1 year^-1, -11.8 kg K ha^-1 year^-1 (for the medium) in the middle landscape, -57 kg N ha^-1 year^-1, -16.1 kg K ha^-1 year^-1 (for the rich) and  -33.5 kg N ha^-1 year^-1, -12.1 kg K ha^-1 year^-1 (for the medium) in the lower landscapes. Less negative value of nutrient balances of the poor socio-economic groups across the three landscapes shows N depletion in the poor socio-economic groups with -17.7kg N ha^-1 year^-1 and -5.59 kg K ha^-1 year^-1,  -21 kg N ha^-1 year^-1 and  -12.8 kg K ha^-1 year^-1 and -19.7 kg N ha^-1 year^-1, and -7.52 kg K ha^-1 year^-1 in the upper, middle and lower landscapes respectively. Soil nutrient stocks in all the landscapes were decreasing with the exception of phosphorus which is positive in all the landscapes. In the analysis, harvested crops (OUT1) and crop residues (OUT2) were the major cause for nutrients depletion.  It was calculated that the contribution of harvested crops (OUT1) and crop residues (OUT2) to N losses was 80.5%, and its contribution to K losses was 65.8%, therefore, application of organic and inorganic inputs, proper management of crop residues and sustaining soil conservation measures are very crucial.

Key words: Resources flow, nutrient balances, soil fertility, landscapes, wealth status.