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.

Automated summary

A two-year microplot experiment was conducted to examine the effects of incorporating spring maize into paddy fields on the utilization of nitrogen (N) fertilizer by late rice. The results showed that the SM-LR system had higher grain yields and total N use of late rice compared to the ER-LR system. However, there was no difference in fertilizer-N use in late rice between the two cropping systems, and the increased total N uptake by late rice was attributed to the utilization of soil-N. Further experiments on soil residual 15N revealed a higher amount of soil residual 15N in the spring maize season, but it had negligible contribution to the N utilization in late rice.