Reduced tillage coupled with straw returning improves grain yield and 2-acetyl-1-pyrroline content in fragrant rice

The practice of conservation tillage or straw returning to the farmland influences the grain yield and quality of rice (Oryza sativa). The key volatile compound responsible for the fragrance in fragrant rice is 2-acetyl-1-pyrroline (2-AP), which is significantly affected by field management measures. The purpose of this study was to investigate the impact of tillage management and straw returning on the grain yield and biosynthesis of 2-AP in fragrant rice. This study was conducted over two years in 2016 and 2017 and utilized two fragrant rice cultivars (Meixiangzhan 2 and Xiangyaxiangzhan) as materials. It consisted of different tillage managements and straw returning treatments, which included three tillage managements: rotary tillage (T0), minimum tillage (T1), and no tillage (T2), and two straw returning treatments: without straw returning (S0) and straw returning (S1). The straw used for the experiment was sourced from the residue of the early season harvested corresponding fragrant rice cultivar. Tillage management and straw returning substantially affected the grain yield, grain quality, and 2-AP content of both fragrant rice cultivars. Compared with the T0S0 treatment, tillage management and straw returning resulted in an improvement in the 2-AP content in 2016 (12.41-116.85%) and 2017 (34.85-103.89%) on average. A higher content of 2-AP was detected in both fragrant rice cultivars in the T2S1 and T1S1 treatments. A structural equation model (SEM) demonstrated that the enzyme activities of fragrance metabolism in the leaves and grain jointly regulated the biosynthesis of precursors of fragrance metabolism in the grain, which further promoted the accumulation of 2-AP. In addition, a principal component analysis indicated that the T1S1 treatment positively correlated with both 2-AP and grain yield. The SEM demonstrated that the enzymes related to nitrogen metabolism, parameters related to photosynthesis, and yield component contributed to the grain yield. The T1S1 treatment resulted in the highest average grain yield of 760.75 g m-2, which can be attributed to an increase in various attributes, such as the leaf area index, SPAD value, nitrogen metabolism, panicle number per m2, and grain number per panicle. The minimum tillage and straw returning (T1S1) treatment is more effective at simultaneously improving both the grain yield and 2-AP content in fragrant rice.