Deep Placement of Fertilizer and Straw Incorporation Improved Grain Yield and 2-acetyl-1-pyrroline (2-AP) of Fragrant Rice

Significance of straw incorporation for crop yield and agricultural sustainability has been well recognized. However, the influence of both deep placement of fertilizer (DPF) and straw incorporation on grain yield and 2-acetyl-1-pyrroline (2-AP) content in fragrant rice is poorly understood. Two fragrant rice varieties, Qingxiangyou 19 xiang (QXY 19X) and Xiangyaxiangzhan (XYXZ), were selected. The experimental design consisted of two straw treatments: with or without straw return (SR/NSR), along with two different fertilizer application methods: one-time deep fertilization (OTDF) and traditional farmer's surface broadcast fertilizer (CF), noted as OTDF-NSR, OTDF-SR, CF-NSR, and CF-SR in order. The results demonstrated that the grain yield of the OTDF-SR treatment was remarkably 28.30-53.62% higher than CF-NSR for two rice cultivars, respectively. The OTDF-SR treatment could significantly increase 2-AP of fragrance rice for both QXY 19X and XYXZ, with value of 24.99% and 28.23% respectively, compared to CF-SR, which was responsible for the increase in proline, pyrroline-5-carboxylic acid, 1-pyrroline, proline dehydrogenase and pyrroline-5-carboxylate synthase. Besides, the photosynthetic trait and SOD activity were increased, while MDA content of flag leaves decreased at heading stage for OTDF-SR. The present study shows that both straw incorporation and fertilizer deep placement mainly improve 2-AP synthesis related enzyme activities and slow down leaf senescence, thus the increase of grain yield and 2-AP of fragrant rice. Hence, it can be regarded as an efficient agronomic method to increase grain yield and 2-AP of fragrant rice.