Effect of irrigation regime on grain yield, water productivity, and methane emissions in dry direct-seeded rice grown in raised beds with wheat straw incorporation

Dry direct-seeded rice grown in raised beds is becoming an important practice in the wheat-rice rotation system in China. However, little information has been available on the effect of various irrigation regimes on grain yield, water productivity (WP), nitrogen use efficiency (NUE), and greenhouse gas emission in this practice. This study investigated the question using two rice cultivars in 2015 and 2016 grown in soil with wheat straw incorporated into it. Rice seeds were directly seeded into raised beds, which were maintained under aerobic conditions during the early seedling period. Three irrigation regimes: continuous flooding (CF), alternate wetting and drying (AWD), and furrow irrigation (FI), were applied from 4.5-leaf-stage to maturity. Compared with CF, both AWD and FI significantly increased grain yield, WP, and internal NUE, with greater increases under the FI regime. The two cultivars showed the same tendency in both years. Both AWD and FI markedly increased soil redox potential, root and shoot biomass, root oxidation activity, leaf photosynthetic NUE, and harvest index and markedly decreased global warming potential, owing to substantial reduction in seasonal CH4 emissions. The results demonstrate that adoption of either AWD or FI could increase grain yield and resource-use efficiency and reduce environmental risks in dry direct-seeded rice grown on raised beds with wheat straw incorporation in the wheat-rice rotation system.