(i) to examine whether introduced cycles of AWD affect ammonia volatilization rates and soil microbial processes leading to increased fertilizer N losses, (ii) to quantify the N flow from 15N-labeled urea fertilizer to the rice crop with special attention to N losses by ammonia volatilization and coupled nitrification-denitrification at different stages of crop growth. Our study was conducted using a systems approach in order to compare two contrasting agricultural systems only differing with regard to water management; i.e. the current best integrated crop management practice for CF irrigated rice in the Mekong delta and its AWD irrigation counterpart.