Fertilizers and the Sustainability of Subsistence Agriculture in Developing Countries.

Fertilizers have frequently been chastised for being unsustainable and destroying soil health. Organic nutrient additions have in many instances shown great promise both to substitute inorganic fertilizers and in some cases even be successful in sustaining nutrient needs in traditional intensive agriculture. However, organic resource availability and its quality are often limited on smallholder farms and agricultural intensification may rely in many situations on net nutrient inputs to farm fields. Additions of green manure and compost to 280 farms as part of conservation farming innovation in Zambia showed limited improvements of maize yields. In contrast, adding recommended rates of inorganic fertilizers on average tripled grain yields. Since imported commercial fertilizers are often unavailable and expensive, additional pathways may need to be explored to improve nutrient use in small-scale subsistence agriculture. One such path to evaluate is the recycling of nutrients from food wastes at the household to the agro-industrial scale. Broad assessments of phosphorus in bones of slaughtered livestock in Ethiopia revealed a theoretical potential of offsetting up to half of the nations imports of phosphorus fertilizers. Generating phosphorus fertilizers from bones were found to be as efficient as imported triple superphosphates on acid weathered soil in both greenhouse and field studies. However, bone distribution networks are fragmented, and amounts available on 518 surveyed farms in four districts in Ethiopia were at most able to satisfy phosphorus needs for kitchen gardens. Innovation in agricultural intensification may benefit from rigorous examination of nutrient recycling from wastes to develop business opportunities that generate innovative bio-fertilizers.