Organic amendments (OA) such as crop residues, manures and composts offer valuable and cost effective sources of nitrogen (N) for tropical agricultural production systems in developing countries. The amount and timing of N available for crop growth following OA application to the soil, however, is difficult to predict due to the complex interactions between added N and associated carbon (C) and the soil microbial biomass, climate, and management. Matching N release from the OA with crop N demand is critical for maintaining adequate crop growth and ensure high yield farmers often over apply N, either as OA or with synthetic fertilizer N. As well as reducing farm profitability, this results in substantial N losses, contributing to pollution of waterways and the production of the powerful greenhouse gas N2O. The proposal will extend two current projects which use the latest greenhouse gas research technology developed in Australia and established in field experiments Sri Lanka and India to improve the N use efficiency (NUE) of key tropical agricultural crops and provide farmers with better tools for predicting N availability from OA. The project has three major aims; (1) quantify N turnover and N2O losses from a range commonly used OA, (2) examine the potential for increasing NUE by better accounting for N in OA and develop recommendations for the use of OA by local farming communities and (3) enhance capacity of global change research in India and Sri Lanka.