Deep placement of liquid fertilizer at tillering stage influences grain quality, 2-acetyl-1-pyrroline synthesis, and antioxidant response of fragrant rice

Abstract

In recent years, the deep placement of solid fertilizers has become popular in rice production due to high fertilizer utilization efficiency and productivity. There is limited knowledge about the effect of deep placement of liquid fertilizer at the tillering stage on grain quality and productivity of fragrant rice. Therefore, a two-year field experiment was conducted from 2019 to 2020 with two fragrant rice cultivars Yuxiangyouzhan (YXYZ) and Xiangyaxiangzhan (XYXZ) under four fertilization treatments: no fertilizer application (T1); application of solid fertilizer (150 kg ha −1 NPK; broadcasted 90 kg ha −1 NPK as basal fertilizer and 60 kg ha −1 NPK at the tillering stage, T2); application of liquid fertilizer with 10 % less N (broadcasted 90 kg ha −1 NPK as basal fertilizer and deeply placed 45 kg ha −1 N and 90 kg ha −1 PK at the tillering stage, T3); application of liquid fertilizer with 20 % less N (broadcasted 90 kg ha −1 NPK as basal fertilizer and deeply placed 30 kg ha −1 N and 90 kg ha −1 PK at the tillering stage, T4). The study showed the highest 2-acetyl-1-pyrroline (2AP) content under T3 treatment (2019, 115.35–120.11 μg kg −1 and 112.97–130.30 μg kg −1 , 2020). The proline (PRO) content, proline dehydrogenase (PDH) activity, 1-pyrrolin-5-carboxylic acid (P5C) content, and 1-pyrrolin-5-carboxylic acid synthase (P5CS) activity also improved under T3 and T4 treatments compared with T2 treatment. Besides, the T3 and T4 treatments increased the protein content and decreased the chalkiness degree and chalky rice rate compared with the T2 treatment. Moreover, T3 and T4 treatments improved the superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities and reduced the malondialdehyde (MDA) content of the leaves compared with the T2 treatment. Further, the structural equation model revealed that POD and CAT and rice appearance quality had significant positive effects on 2AP content, and that POD and CAT indirectly affected 2AP content by showing a significant positive effect on the PRO. The T3 treatment also showed relatively stable and higher head rice yield and net income in the two-year field experiment. Overall, side deep placement of liquid fertilizer improved the 2AP synthesis, and antioxidant response of fragrant rice and under T3 treatment, the head rice yield was stable and the economic income was higher. Therefore, in the future of agricultural production, it is recommended that farmers use liquid fertilizer with 10 % less N (T3) to improve the quality and stress resistance of fragrant rice and obtain stable and more economic benefits. • Deep placement of liquid fertilizer at tillering stage improved 2-acetyl-1-pyrroline and grain quality of fragrant rice. • Deep placement of liquid fertilizer at tillering stage enhanced antioxidant enzyme activities in leaves of fragrant rice. • The relationship among antioxidant response, 2-acetyl-1-pyrroline, and grain quality in fragrant rice were interpreted. • Optimization of deep placement of liquid fertilizer at the tillering stage yield higher economic income.