Responses of soil aggregates, organic carbon, and crop yield to short-term intermittent deep tillage in Southern China

Long-term shallow rotary tillage has reduced the soil quality and restricted the crop yield growth of farmland in Southern China. Deep tillage can effectively loosen the soil and reduce the compaction of deep soil, while no-tillage can ensure the sustainable use of soil. In this study, we selected three paddyupland multiple cropping rotation areas in Southern China. Two tillage regimes were carried out, one (DT) where rice straw mulching was followed by deep tillage (subsoiling 30 cm) and then, for the next three years, no-tillage in the flue-cured tobacco planting season and rotary tillage in the rice planting season vs a control (RT) where no tillage after rice straw mulching was carried out, and rotary tillage was conducted in both the flue-cured tobacco planting season and rice planting season for the next three years. We compared the yield and output value of flue-cured tobacco and grain yield under DT and RT tillage regimes in the three areas, and analyzed the economic benefits brought by DT. Furthermore, we identified the effects of DT on soil aggregates, soil organic carbon (SOC), crop growth, and nutrient uptake at the experimental site in Yunyuan. Compared with RT, DT can increase the weight proportion of macroaggregates and SOC content in the 10-30 cm soil layer and improve the stability of soil aggregates in the 0-30 cm soil layer. In 2019, the mean weight diameter (MWD) and geometric mean diameter (GMD) of the 0-30 cm soil layer increased by 0.47 mm and 0.20 mm, respectively, on average. In 2020, the MWD and GMD increased by 0.33 mm and 0.11 mm, respectively, on average. DT promoted the roots of flue-cured tobacco to extend down to the 30-40 cm soil layer, and DT flue-cured tobacco plants had more leaves, higher dry matter weight, and greater N and P absorption than RT flue-cured tobacco. These results were conducive to the increase of yield and output value of flue-cured tobacco. During the threeyear test period, the yield of flue-cured tobacco increased by 4%-9%, the output value increased by 7%-13%, and the net economic benefits also increased. In the paddy-upland multiple cropping rotation areas of Southern China, DT is more conducive to the improvement of dryland crop yield than paddy field crop yield. Intermittent deep tillage (one-time deep tillage and then no tillage) is expected to provide a potential way to effectively increase production, high economic efficiency, and soil improvement in promoting sustainable agricultural development and cleaner production.