Uptake efficiency of 15N-urea in flooded and aerobic rice fields under semi-arid conditions
The sustainability of traditional rice (Oryza sativa L.) cultivation in many Asian countries is being questioned due to severe water shortage conditions, envisaging the need for development of water-saving rice production technologies. A 2-year-field study on a typic Haplustalf soil was conducted to compare traditional transplanted rice–maize system with water-saving aerobic rice–maize system, with an overall objective of investigating the fate of fertilizer nitrogen (N) using 15N-labeled urea. Results from the field experiments showed that the rice plants positively responded to N fertilizer application. The average fertilizer N recovery by rice crop over the 2 years in aerobic rice was 26 kg per 100 kg of applied fertilizer N in the main field and 21 kg per 100 kg of applied N in the microplot, while the recoveries were 41 and 32 kg ha−1 per 100 kg of applied N in traditionally cultivated rice under flooded conditions. The fraction of 15N that was found in soil after the harvest of rice crop ranged from 11.4 to 47.1 kg ha−1 in aerobic rice and 14.2–51.4 kg ha−1 in flooded rice. Average recovery of 15N fertilizer in maize after the first growing season was 3.3 %, and the corresponding recovery in soil was 19 %. An additional 1.3 % of the fertilizer was recovered by crops during the two subsequent seasons. This study indicates the need to develop management practices that improve N use efficiency in aerobic rice by reducing losses to improve yields and reduce N export to the environment.