Assessing the Management of Nitrogen Fertilizer Levels for Yield Values, Photosynthetic Characteristics and Non-Structural Carbohydrates in Rice

Abstract

The interaction between the amount and frequencies of nitrogen application has always been a hot issue in improving crop yield and reducing environmental pollution. Photosynthesis and non-structural carbohydrates (NSCs) play an important role in the formation of rice yield. However, the research on photosynthetic characteristics and NSCs under nitrogen fertilizer management on rice yield is still insufficient. This work was a two-year field trial in China’s Hunan Province in 2020–2021. To analyze the photosynthetic characteristics and NSCs of the hybrid rice “Zhu Liangyou 819” (ZLY819), the experiment was set up with N application frequencies, specifically P1 (basal-tiller fertilizer at a ratio of 5:5), P2 (basal-tiller-spike fertilizer at a ratio of 4:3:3), and P3 (basal-tiller-spike-grain fertilizer at a ratio of 4:3:2:1). Additionally, three distinct amounts of N applications were utilized: N1 (90 kg ha−1), N2 (150 kg ha−1), and N3 (210 kg ha−1). The findings indicated that under the same N application amount, N2 increased the effective spike by 9.32–17.80% and the number of grains per spike by 12.21–13.28% compared with N1. Under the same N application frequency, P3 had the highest effective number of spikes and number of grains per spike, which were 320.83 × 104 ha−1 and 113.99–119.81, respectively. Under the same N application amount, the SPAD and photosynthetic rate (Pn) of N2 at the heading stage were increased by 5.61–5.68% and 11.73–13.81%, respectively, compared with that of N1; and at the maturity stage, the SPAD of N2 was increased by 14.79–17.21%. At the same N application frequency, SPAD and Pn were 5.40–6.78% and 4.70–12.85% higher in P3 compared to P1, respectively, at the heading stage. At maturity, SPAD showed 14.59–15.64% higher values in P3 compared to P1. The photosynthetically active radiations (PAR) and radiation use efficiency (RUE) of ZLY819 obtained the highest values under N2 or N3 as the differences between these both were nonsignificant. PAR and RUE tended to increase with the increase in the application frequency. NSC accumulation, output, and contribution rate to grains all exhibited a pattern of initial increase followed by a subsequent decline in response to escalating nitrogen application, i.e., it was highest under N2 treatment. A statistically significant positive correlation was observed between rice yield and effective number of spikes, number of grains per spike, SPAD, Pn RUE, output of NSCs, and contribution rate to grains. Appropriate amount and frequency of N application (P3N2) can significantly improve photosynthetic characteristics and NSCs of rice, thus increasing rice yield.