Triangular Transplanting Pattern and Split Nitrogen Fertilizer Application Increase Rice Yield and Nitrogen Fertilizer Recovery

Field experiments were conducted to evaluate the effects of improved crop management (OPT) for irrigated rice (Oryza sativa L.) on grain yield and N recovery efficiency in southwestern China. In the OPT treatment, rice seedlings were transplanted in a triangular spatial pattern and the N fertilizer was split, based on the difference between the estimated total N requirement and the soil and environmental N supply. Fine-tuning of application rates was achieved using leaf greenness measurements. The performance of OPT was tested in two adjacent fields in which the crops preceding rice were wheat (Triticum aestivum L.; R-w) and rapeseed (Brassica napus var. napus; R-o). The OPT and traditional farming practice (TRA) treatments both gave higher average grain yields than zero-N controls (CK). Rice yields were considerably smaller in R-w than R-o under CK. Compared with TRA, OPT led to significantly higher aboveground N uptake, biomass accumulation, and grain yield in R-w. Over the 2 yr of the study, average rice grain yields under OPT increased by 19 and 22% compared with TRA and 30 farmers' fields, respectively. The OPT treatment performed better than TRA in N-15 recovery efficiency. Compared with TRA, OPT led to increased N-15 fertilizer recovery efficiency from 19% in TRA to 42% in OPT, and decreased loss from 68% in TRA to 39% in OPT. In conclusion, OPT practice is a feasible means to attain increased yield with efficient N use. This study provides guidance for farmers using rice-based cropping systems, especially in southwestern China.