Effects of Organic Fertilizer Substitution for Chemical Fertilizer on Grain Yield and 2-Acetyl-1-pyrroline (2-AP) of Fragrant Rice

Organic fertilizer replacing a portion of chemical fertilizers is a key strategy for improving grain qualities and economic benefits. Fragrant rice, favored by consumers for its superior quality and rich aroma, has garnered significant attention. However, there is little information on the effect of organic fertilizer replacing a portion of chemical fertilizers on the grain yield and 2-AP of fragrant rice. Taking Meixiangzhan2 and Qingxiangyou19 as experimental materials, five different experimental treatments were designed: all urea (T1), 33.3% organic fertilizer substitution for urea (T2), 66.7% organic fertilizer substitution for urea (T3), all organic fertilizer (T4), and no fertilizer as a control (CK). The results showed that the T2 treatment could significantly increase the grain yield of Meixiangzhan2 to 62.50 g·pot−1 and Qingxiangyou19 to 67.88 g·pot−1 due to the increase of 27.90% and 26.03% over T1, and 72.18% and 59.45% over CK, respectively. Compared with T1, the T2 treatment could markedly enhance the 2-AP content in Meixiangzhan2 (418.01 μg kg−1, up by 7.70%) and Qingxiangyou19 (378.53 μg kg−1, up by 9.12%). Relative to CK, the aroma content of these two varieties under the T2 treatment rose by 22.05% and 31.04%, respectively. The main reasons were due to the increase in pyrroline-5-carboxylic acid, 1-pyrroline, proline dehydrogenase, and pyrroline-5-carboxylate synthase. The dry matter accumulation, leaf area, and photosynthetic rate of Meixiangzhan2 and Qingxiangyou19 were also significantly increased, and the activities of nitrate reductase and glutamine synthetase were also significantly improved. Moreover, the activities of peroxidase and catalase in rice sword leaves were remarkably improved, and the content of malondialdehyde was significantly decreased. The results showed that 33.3% of organic fertilizer instead of chemical fertilizer had the positive effect of increasing the grain yield and improving the aroma of rice, which was worth further popularization and application.