Nitrogen fertilizer management for high nitrogen utilization efficiency and rice yield under straw incorporation in a cold region

Objectives In the cold rice-growing region, straw incorporation is a popular technology for sustaining soil fertility. Here, we studied the allocation of N fertilizer ratio for basal-tillering and panicle stage of rice production to provide a scientific basis for the rational application of N fertilizer in this region.

Methods Field experiments were conducted in 2016 and 2017 in Jilin Province, using rice cultivar Jijing 511 as test materials. In the previous year, 9000 kg/hm² rice straw was cut to about 10 cm long and buried into the soil with a plough. Using a total of 200 kg/hm² N fertilizer, five basal-tillering/panicle application ratios were set up, including 5∶5 (N 5∶5), 6∶4 (N 6∶4), 7∶3 (N 7∶3), 8∶2 (N 8∶2), 9∶1 (N 9∶1), and no N fertilizer application (N0) used as the control. The rice plant’s dry matter and N content were analyzed in 6 growing stages, and yield and its components were investigated at harvest. The N accumulation dynamics, translocation characteristics, and N utilization efficiency were calculated.

Results Compared with N0, N fertilizer application improved panicle number, grain number per panicle, and seed-setting rate of rice, and significantly increased yield as a result. Rice yield reached the highest in the N 8∶2 treatment. N accumulation from returning green stage to jointing stage increased with increased N ratio in basal-tillering stage, but that from the full heading stage to maturity stage increased first and then decreased, with the highest value in N 8∶2 treatment. N fertilizer application significantly increased N translocation and accumulation in the rice grains after the full heading stage. N translocation increased with an increased ratio of N in the basal-tillering stage. Moreover, accumulated N in the rice grains at the full heading stage increased firstly and then decreased, reaching the highest in the N 8∶2 treatment. Correspondingly, all the N recovery efficiency, agronomic efficiency, partial factor productivity, and physiological efficiency reached the highest in the N 8∶2 treatment. Correlation analysis showed a significant positive relationship between yield and N accumulation at the full heading stage (r = 0.8943−0.9476). However, after the full heading stage, the correlation coefficient was higher than the value recorded before this stage.

Conclusions Under straw incorporation, the 8∶2 N fertilizer treatment for basal-tillering and panicle stage of rice production had the highest N accumulation from the full heading stage to maturity stage, increased N translocation to grains, improved yield, and N utilization efficiency. Therefore, under the experimental conditions, we recommend using 200 kg/hm² N fertilizer at 8∶2 for basal-tillering and panicle stage of rice production to optimize N accumulation characteristics and improve yield.