Effects of Dense Planting with Less Nitrogen Fertilization on Rice Yield and Nitrogen Use Efficiency in Northeast China

The mode of sparse planting with high N(nitrogen) application in Northeast China is not conducive to high and stable yields nor efficient use of resources. This study investigated if dense planting with less N fertilization in rice could improve nitrogen use efficiency (NUE) and increase yield in Northeast China. we conducted a field experiment using Jijing 88 and Tonghe 99 as planting material and setting three cropping modes of dense planting with less N (T1: 30 cm × 13.3 cm, 200 kg·ha−1; T2: 25 cm × 13.3 cm, 175 kg·ha−1; T3: 25 cm × 10 cm, 150 kg·ha−1) and a local conventional cropping pattern (CK: 30 cm × 16.5 cm, 225 kg·ha−1). The results showed that, when compared to CK, dense planting with less N application (T1, T2) increased the maximum tiller number, above-ground biomass and obtained higher panicle number per m−2 and grain filling rate. The maximum yields of Jijing 88 occurred with T1, which increased by 1.29% on average compared to CK; The maximum yields of Tonghe 99 occurred with T2, which increased by 3.50% on average compared to CK. The T1and T2 increased apparent recovery efficiency of nitrogen fertilizer (REN), agronomic nitrogen use efficiency (AEN), internal nitrogen use efficiency (IEN) compared to CK. Together, reducing N rate from 225 kg·ha−1 (CK) to 175 kg·ha−1 (T2) could obtained resulted generally equal or higher grain yield and higher NUE with increasing transplanting density from 30 cm × 16.5 cm (CK) to 25 cm × 13.3 cm (T2), and dense planting is a feasible strategy to reduce N input in Northeast China.