Effects of nitrogen, phosphorus and potassium fertilizer rates on yield and grain quality of soft japonica rice under straw returning condition

Objectives Straw returning and machanical transplanting technologies have been widely extended in the rice production. This paper studied the effects of the rates of nitrogen (N), phosphorus (P) and potassium (K) on grain yield and quality of soft japonica rice under the technologies, in order to propose the appropriate fertilization measurements.

Methods Field experiments were conducted in Diaoyu Town, Xinghua City, Jiangsu Province in 2014 and 2015, using a good eating quality rice cultivar Nanjing 9108 as tested materials. Taking the recommended N 270 kg/hm², P 108 kg/hm² and K 216 kg/hm² for rice in the area as level 2, six levels were tested for all the N, P and K fertilizers as 0, 1, 1.5, 2, 2.5, 3. The grain yield and quality were investigated.

Results The main nutrient affecting rice yield and quality was N, then was K and P. Within the tested N levels, the highest rice yield was obtained in level 2; the brown rice percentage (BR), milled rice percentage (MR), head rice percentage (HR) and protein content (PC) were increased with the increased N levels, the amylose contents (AC) were reduced on the contrary, and the gel consistency (GC) was shorten, the peak viscosity and breakdown were declined, the trough viscosity and setback were increased; the differences of these rice quality indices were significant between the high (N3) and low nitrogen (N1) treatments. Within the tested P levels, the rice yields were relatively high in level 2; the processing quality of rice were improved with the increased P levels, and there was no differences in PC, AC and GC, but the RVA profile of starch showed worse. Within the tested K levels, the highest rice yield was obtained in level 2, BR, MR and HR were increased to the maximum in level 2.5 and then decreased, PC was increased, AC was decreased, the peak viscosity and breakdown were increased and then decreased, the setback was decreased and then increased.

Conclusions Under the experimental condition, suitable rates of N, P and K fertilizers could enhance rice processing quality and yields, N plays greater role than P and K. Comprehensively considering the yield, quality and economic profit, the recommended N 270 kg/hm², P 108 kg/hm² and K 216 kg/hm² for rice could coordinate preferably high-yield and good quality of rice.