Nitrogen and potassium interactions optimized asynchronous spikelet filling and increased grain yield of japonica rice

Abstract

Poor grain filling severely reduces rice yield. Fertilizers play a vital role in regulating grain filling, especially nitrogen (N) and potassium (K). In this field study we aimed to investigate the interactive effects of N and K on the asynchronous filling properties of superior and inferior spikelets of japonica rice. We looked at grain filling under three N rates (0, 90, and 180 kg N ha^-1) and three K rates (0, 60, and 120 kg K₂O ha^-1) during 2020 and 2021. Across two years, the results showed that the combined use of N and K on superior and inferior spikelets significantly increased their weight by 1.29 mg and 2.31 mg, their maximum grain filling rate by 0.24 mg d^-1 and 0.07 mg d^-1, and their average grain filling rate by 0.21 mg d^-1 and 0.06 mg d^-1, respectively, in comparison with the control (N0K0) treatment. Likewise, K supply increased the average contribution rate of superior and inferior spikelets to yield by 9.1% and 10.0%, respectively. Correlation analysis showed that the grain filling rate of superior and inferior spikelets was an important factor in determining the spikelet weight, whereas the grain filling time was not. We also found that the 1,000-grain weight mainly increased after increasing the spikelets' maximum grain filling rate and average grain filling rate. Collectively, these results illustrate that the combined use of N and K can optimize the asynchronous filling of superior and inferior spikelets and, in particular, enhance inferior spikelet weight with higher rice yield.

Keywords: Asynchronous filling; Interaction effects of nitrogen and potassium; Japonica rice; Superior and inferior spikelets.

Figure 1. Statistics of precipitation and temperature during rice growing season in 2020 (A) and 2021 (B).

Note: red line represents the average temperature, blue columns represents precipitation.

Figure 2. Grain filling curves of rice under different N and K treatments in 2020 (A) and 2021 (B).

Note: blue curve represents the inferior spikelets, red curve represents the inferior spikelets.

Figure 3. Grain filling rate curves of rice under different N and K treatments in 2020 (A) and 2021 (B).

Note: blue curve represents the inferior spikelets, red curve represents the inferior spikelets, t₁ represents the start of the rapid growth stage, t₂ represents the maximum growth stage, t₃ represents the end of the rapid growth stage.

Figure 4. Correlation between grain filling characteristic parameters of superior and inferior spikelets with 1,000-grain weight.

Note: blue and red represents positive and negative correlations, the size of the circle represents the strength of the correlation, S represents the superior spikelet, I represents the inferior spikelet, Gm represents the maximum growth rate, Ga represents the average growth rate, D represents the duration of the rapid growth stage, Tm represents the date when the maximum growth stage is reached, W represents the spikelet weight, G represents the 1,000-grain weight, ** represents statistical significance at P < 0.01, * represents statistical significance at 0.01 < P < 0.05.