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

The practice of conservation tillage or straw return to the farmland influences the grain yield and quality of rice (Oryza sativa). The key volatile compound responsible for the fragrance of 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 return on the grain yield and biosynthesis of 2-AP in fragrant rice. This study was conducted over two years in 2016 and 2017 and used two fragrant rice cultivars (Meixiangzhan 2 and Xiangyaxiangzhan) as materials. The experimental design consisted of different tillage management and straw return treatments, which included three tillage management regimes: rotary tillage (T0), minimum tillage (T1), and no tillage (T2); and two straw return treatments: without straw return (S0) and straw return (S1). The straw used for the experiment was sourced from the residue of the corresponding fragrant rice cultivar harvested in the early season. Tillage management and straw return substantially affected the grain yields, grain quality, and 2-AP contents of both fragrant rice cultivars. Compared with the T0S0 treatment, tillage management and straw return resulted in 2-AP content improvements in 2016 (12.41–116.85%) and 2017 (34.85–103.89%) on average. Higher 2-AP contents were also detected in both fragrant rice cultivars in the T2S1 and T1S1 treatments. A structural equation model (SEM) demonstrated that the activities of enzymes related to 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 was 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 components contributed to the grain yield. The T1S1 treatment resulted in the highest average grain yield of 760.75 g m^–2, which could be attributed to increases in various attributes, such as the leaf area index, SPAD value, nitrogen metabolism, panicle number m^–2, and grain number per panicle. In summary, the minimum tillage and straw return (T1S1) treatment is more effective at simultaneously improving both the grain yield and 2-AP content in fragrant rice.