Humic Acid Fertilizer Incorporation Increases Rice Radiation Use, Growth, and Yield: A Case Study on the Songnen Plain, China

Abstract

Humic acid fertilizer (HA) incorporation is a common method for improving crop growth and soil fertility. However, the effects of HA incorporation on rice growth are still unknown. We conducted a two-year field experiment to determine the radiation use, growth, and yield of rice grown with five different HA rates: 110 kg∙ha−1 100% urea (pure nitrogen) (T1); 30% HA and 70% urea (T2); 50% HA and 50% urea (T3); 70% HA and 30% urea (T4), and 1500 kg∙ha−1 100% HA (T5). The results showed that the T2 treatment had the lowest values of photosynthetic efficiency of PSII (Fv/Fm), relative leaf chlorophyll content (SPAD), plant height and leaf area index (LAI) in both years, which were similar to the photosynthetically active radiation (IPAR), radiation use efficiency (RUE), yield, and biomass. In contrast, the highest harvest index (HI) value was found in the T2 treatment. In the two years, the T4 and T5 treatments showed no significant differences. However, the multivariate statistical method based on principal component analysis showed that in the first principal component, the LAI, biomass, yield, plant height, SPAD, Fv/Fm, IPAR, and RUE had a positive correlation, and the HI had a negative correlation. The LAI, yield, plant height, SPAD, HI, and RUE had a positive correlation, but biomass, Fv/Fm and IPAR had a negative correlation in the second principal component. Across the different HA treatments, the comprehensive scores were T5 > T4 > T3 > T1 > T2, with values of 2.13, 1.38, −0.17, −0.34, and −3.00, respectively. According to the principal component analysis results of each index, the T5 treatment was better than the T4 treatment.