Incorporation of spring maize into paddy fields increased nitrogen uptake in late rice by enhancing soil nitrogen supply: Field 15N tracer studies

To assess the impacts of the incorporation of spring maize into paddy fields on the utilization of nitrogen (N) fertilizer by late rice, a two-year microplot experiment was performed using labeled 15N-urea to trace the fate of N fertilizer in spring maize-late rice (SM-LR) and early rice-late rice (ER-LR) systems. Compared with ER-LR system, SM-LR system showed higher grain yields and total N use of late rice. However, no difference in fertilizer-N use in late rice between the two cropping systems, and the utilization of soil-N rather than fertilizer-N was responsible for the increased total N uptake by late rice. Further microplot experiments on the fate of soil residual 15N showed a greater amount of soil residual 15N in the spring maize season than in the early rice season (122 vs. 72 kg N ha-1). However, soil residual 15N from the first season had a negligible contribution to the utilization of N in late rice. We conclude that the improvement in the soil N supply accounts for the increased total N use in late rice under the incorporation of spring maize into paddy fields.