Abstract
On smallholder farms in Ethiopia, livestock manure and organic residues are traditionally removed from fields for construction, feed, and fuel purposes, while the remainder stays in the field as feed or fertilizer. Burning and removing organic matter without replacing it leads to valuable losses of on-farm nutrients and soil carbon, which could otherwise be used to fertilize crops. Instead, resources need to be used efficiently by reducing and recycling organic residues and forming a closed production system. Competition between applications can be eliminated by bio-methanation using a biodigester. There, organic residues are transformed to biogas utilized for light and cooking and bioslurry, a nutritious organic fertilizer and source of organic matter. Through capturing nutrients in agricultural by-products, nutrients become available to the food system again. Literature review has been supplemented with empirical evidence from a study carried out in the central Ethiopian Highlands on 47 smallholder farms, to provide a baseline for further improvements on the management of biogas technology. The study identifies a series of inadequate handling practices and thus a significant potential to optimize the farming system around a biodigester. It is recommended to include forage legumes in the farm system to enhance on-farm available nutrients that can be recycled through a biodigester. It is further necessary to involve the private sector in biodigester programs, to improve local availability of materials, which are suitable to the local culture and traditions. Space for knowledge exchange between farmers and advisors like demonstration farms can further improve bioslurry management. Although challenges remain, the integration of a biodigester should be encouraged as it fulfills the production of energy and a nutritious and economic fertilizer without additional resources, resulting in a win-win situation for the farmer.
Highlights
With an increasing population and decreasing availability of agricultural land, pressure on resources required for crop production is growing (Rahmann et al 2019)
The current situation on smallholder farms in Ethiopia shows that valuable nutrients and organic matter are often lost from farms, as organic residues are removed for fuel, feed, and construction purposes which could otherwise be used to fertilize crops
The main objective of this paper is to evaluate the performance of biodigesters and its impact on farm nutrient flows by analyzing the management of liquid
Summary
With an increasing population and decreasing availability of agricultural land, pressure on resources required for crop production is growing (Rahmann et al 2019). To cover food demand for the rising population with limited resources, organic matter residue losses should be avoided and biomass and its nutrients recycled (Smith et al 2014). The current situation on smallholder farms in Ethiopia shows that valuable nutrients and organic matter are often lost from farms, as organic residues are removed for fuel, feed, and construction purposes which could otherwise be used to fertilize crops. Chemical fertilizers can be applied to replace nutrients removed from harvested crops, it is expensive to administer, requires fossil fuels, reduces the pH value in often already acidic soils, and is harmful to the environment, due to a lack of knowledge and adapted application technologies. The optimization of the endogenous potential of smallholder farms to recycle farm internal nutrients is a priority
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