Re-sourcing soil fertility : assessing the soil amendment potential of farm household resources and wastes in Bolo Silasie, Ethiopia
Abstract: The global agriculture of today is to a high degree dependent on mineral fertilisers that through a constant accumulation of nitrogen (N) and phosphorus (P) in the biosphere contribute to greenhouse gas emissions and eutrophication of water bodies. At the same time, agricultural productivity around the world is largely constrained by low inputs of plant nutrients. Increased nutrient recovery from organic wastes and livestock and human excreta is needed to sustain soil fertility and ensure food security within the planetary boundaries. In this study, the resource management in Ethiopian farm households (hhs) has been studied to assess to what extent N, P and organic carbon (OC) could be recirculated to farmland from local farm household resources and wastes. The study included 15 farm hhs divided into three different socio-economic groups in the village of Bolo Silasie in central Ethiopia. The data collection was done through interviews, collection and weighing of waste fractions and lab analyses of total N, total P and OC for the most important farm resources and wastes. To understand the dynamics of nutrient accumulation and losses in the farm system, the data was analysed using material flow analysis (MFA). Additionally, 24 fields belonging to the study hhs were sampled and analysed to assess their current soil status in the village. It was found that although livestock are crucial components in the local farming system, only 19% of the manure is returned to the fields through compost application. Finding an alternative to the current use of manure as stove fuel was identified as the intervention with the highest poten-tial for increased nutrient and organic matter recovery. Utilization of livestock urine and hu-man excreta as well as improved management of compost could also make significant con-tributions to improved nutrient recovery. Depending on resource recovery ambition, local resources could supply up to 50 kg N and 12 kg P ha-1 y-1. This should be compared to the current use of mineral fertilizers of 51 kg N and 26 kg P ha-1 y-1. Today, however, many hh resources and wastes have an alternative use, and any intervention in the management system must be considered together with its social, practical and ecological implications. The three socio-economic groups were found to face different challenges and opportunities in nutrient recycling, mainly related to differences in access to livestock. This study hence suggests that research and advisory around local plant nutrient management should pay greater to socio-economic factors influencing hh resource and waste management.
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