Effects of nitrogen application method and bud-promoting nitrogen fertilizer rate on yield and quality of ratoon rice

Objectives The rational application of bud-promoting fertilizer and seedling promoting fertilizer is an important way to ensure the optimum yield and quality in rice ratoon season. It is of great significance to clarify the reasonable nitrogen management mode and the rate of germination promoting nitrogen fertilizer in ratoon season to improve the yield and optimize the quality of ratoon rice.

Methods In this study, a multi-year field experiment was conducted with Shenliangyou 5814 cultivar. Five nitrogen fertilizer treatments were set up: no nitrogen fertilizer (N_0-0) in the regenerative season; bud-promoting N 60 kg/hm² (N_60-0); seedling-promoting N 60 kg/hm² (N_0-60); bud- and seedling-promoting N 60 kg/hm² each (N_60-60); bud-promoting N 120 kg/hm² and seedling-promoting N 60 kg/hm² (N_120-60). The nitrogen fertilizer was applied in the regenerative season. The growth, yield and yield components of ratoon rice were investigated.

Results Although there were large variations in the yields of the three-year trials, the nitrogen application treatments in the same year could significantly improve the yield of ratoon rice. Compared with N_0-0 treatment, N_60-0, N_0-60, and N_60-60 treatments increased production by 35.8%, 40.9%, and 67.4%, respectively. The combined application of bud-promoting fertilizer and seedling- promoting fertilizer further increased the yield of ratoon rice by increasing the number of effective panicles and grains per panicle. With the increase of nitrogen fertilizer application rate, the yield increased firstly and then became stable. The suitable combination of bud-promoting fertilizer and seedling-promoting fertilizer promoted the germination, formation, growth, and development of regenerated buds, and significantly increased the number of effective panicles and grains per panicle at 2^nd and 3^rd nodes (especially 3^rd nodes). Further, with increasing nitrogen application rate, nitrogen uptake in shoot of ratoon rice increased significantly. Compared with N_0-0 treatment, N_60-0, N_0-60, N_60-60 and N_120-60 treatments increased nitrogen uptake by 51.31%, 57.70%, 91.33%, and 124.53% on average, respectively, but the NUE exhibited a decreasing trend. In terms of quality, increasing rate of the nitrogen fertilizer led to an initial increase in the processing quality, appearance quality, and amylose content of ratoon rice but they later decreased, while the protein content increased gradually. Compared with other treatments, the processing quality and appearance quality of ratoon rice were optimized when the combination of bud-promoting fertilizer and seedling-promoting fertilizer was applied at N_60-60. Compared with N_0-0 treatment, brown rice rate, milled rice rate and head milled rice rate of N_60-60 treatment were increased by 2.7%, 1.3%, and 6.7%, respectively. Chalkiness and chalkiness grain rate decreased by 13.8% and 22.6%, respectively. However, when bud-promoting fertilizer application rate increased further (N_120-60), the processing quality and appearance quality of rice were reduced, with the head milled rice rate decreasing and chalkiness grain rate increasing most significantly.

Conclusions Under this experimental conditions, the application of N 60 kg/hm² bud-promoting fertilizer and 60 kg/hm² seedling-promoting fertilizer significantly improves the yield, nitrogen use efficiency, and rice quality.