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.
Highlights
Agriculture is the main economic activity of Ethiopia
The results of the partial nutrient balance showed that the nutrient removals by the crop harvest and crop residues were the greatest contributors to the N and K negative balances except for the phosphorous in the three landscapes and in all the socio-economic groups, in the case of rich farmers in the middle landscape. These differences are associated with the differences in crop production, that is, higher crop production by rich farm group
These differences are associated with the differences in crop production as the result of chemical and physical soil fertility of the cultivated fields of the rich is generally higher and these rich farmers implement more frequently nutrient-saving techniques, such as soil and water conservation practices and apply more external and internal inputs
Summary
Agriculture is the main economic activity of Ethiopia. It is dominated by smallholder farming (MoFED, 2002; CSA, 2009). Over 50% of the highlands in general and cropped areas of Ethiopia are in an advanced stage of land degradation (Elias, 2002). This is because of the continuous cultivation at least since the 13th century (Tewolde Berhan, 2006). The soil depth in many areas of Ethiopia is less than 20 to 30 cm, this means that it is reaching the lower limits of productivity of the arable land and has lost much of its capacity to retain moisture; with consequent decline in agricultural yield (Stocking and Murnaghan, 2001; Elias, 2002; World Bank, 2007). This kind of information is critical for decision makers to plan and implement integrated nutrient management strategies at a regional and catchment level
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