Developing an economic, environmental and agronomic case for the increased use of organic amendments in South Asia

Abstract

Aggressive fertilizer subsidies throughout South Asia have led to a rapid increase in the use of synthetic nitrogen fertilizers such as urea at the farm level. While this has been successful in increasing yields, significant yield gaps remain between potential and actual farm yields, while unbalanced or over application of fertilizers potentially damages soil and environmental health. This project examined organic amendment (OA) application in India and Sri Lanka on productivity, soil properties and greenhouse gas emissions. In India, poultry, farm-yard manure and vermi-compost were applied to a paddy rice crop, and the potential benefits followed through to a post-rice chickpea crop. In Sri Lanka, we tested the optimal combination of synthetic nitrogen fertilizer rates when using municipal-waste compost in a multi-year maize-soybean rotation. Results at both trial sites saw an increase in crop yields under OA application; in particular chickpea yields from farm-yard manure and after repeated application of municipal-waste compost. However, all OA treatments increased emissions of the greenhouse gases nitrous oxide and methane due to additional nitrogen or carbon availability. Furthermore, the low nutrient content and relatively high cost of the OA’s, particularly the composts, made them uneconomical as nutrient sources compared to conventional fertilizers.