Effects of One-Time Reduced Basal Application of Controlled-Release Nitrogen Fertilizer with Increased Planting Density on Yield and Nitrogen Utilization of Mechanically Transplanted Japonica Rice

The excessive application of nitrogen (N) fertilizer can result in soil and water pollution, thereby negatively impacting the ecological environment. However, reducing the amount of N fertilizer may lead to a decrease in crop yield. Two years’ experiment (2021 and 2022) investigates the influence of one-time reduced basal application of controlled-release N fertilizer (CRU) and increased planting density on the grain yield and N utilization characteristics of mechanically transplanted japonica rice. Nanjing 5718 was used as the experimental material. Under the condition of 225 kg ha−1 of N, three controlled-release periods of CRUs (60d, 80d, 100d) and three planting densities (6, 8, and 10 seedlings/hole) were combined, totaling nine combinations. Moreover, a conventional split fertilization treatment with 300 kg ha−1 of N and a planting density of 4 seedlings/hole was set as the control (CK). The yield, dry matter accumulation, N accumulation, and N utilization efficiency were evaluated. The research findings demonstrate that the CRU80-6 treatment exhibited the highest efficacy among all N reduction and density increase treatments, resulting in a significant yield increase of 3.1–10.3% compared to other treatments. After the jointing stage, the CRU80-6 treatment exhibited the highest dry matter accumulation compared to other treatments, with an increase ranging from 0.8% to 13.6%, and was significantly lower than that of the CK by 4.3% to 5.0%. The N accumulation and translocation traits of the CRU80-6 treatment closely resembled those of CK. However, both N recovery efficiency (NRE) and N agronomic efficiency (NAE) exhibited a remarkable increase compared to CK, with an average enhancement in NRE of 30.01%. Therefore, we contend that the CRU80-6 treatment, with a 25% reduction in N input, can ensure efficient N utilization and attain a relatively stable grain yield.