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Crop straw return is one of the most important measures to increase soil organic carbon (SOC) content in farmland systems. However, the effects of crop straw return amount on SOC sequestration (SCS) in long‐term crop rotation system is unclear, especially in typically cool and dry regions. A field experiment was conducted from 2015 to 2020 in a wheat‐maize‐potato rotation system including four straw treatments: without straw incorporation (CK), 1/3 straw incorporation (LS), 2/3 straw incorporation (MS), and all‐straw incorporation (HS), respectively. After 6 years of cropping, SCS in 0–30‐cm soil layer of CK, LS, MS, and HS increased by 3.6, 7.0, 7.8, and 9.9 Mg ha−1, compared with the beginning of the experiment, respectively. In particular, SCS in 20–30‐cm soil layer of CK was obviously increased by 2.7 Mg ha−1. When compared with CK, straw incorporation increased total dry matter, total evapotranspiration, SCS, and water productivity by 29.3%, 3.4%, 28.8%, and 25.2% on average, respectively, but decreased pure carbon accumulation and water use efficiency of carbon sequestration. Although the carbon input and SCS showed a linear positive correlation with evapotranspiration, the carbon input efficiency was negatively correlated with pure carbon accumulation in HS and MS. When compared with LS, the carbon input efficiency decreased by 64.1% in HS, restricting SCS. These results indicated that 1/3 straw incorporation could increase SCS efficiency as well as decrease carbon loss in the–crop system, making it more suitable for application in cool semiarid region, and revealed that excessively straw returning to the field could not improve SCS efficiency. [ABSTRACT FROM AUTHOR]

Forage maize is one of the most important feed crops for livestock production, and is mainly grown in northwest China. However, their growth is often stressed by limited soil water availability due to the arid climate. To provide more soil moisture, a high-efficiency tillage technique was required to make crops effectively use soil moisture in deep soil layers. Deep vertical rotary tillage is a promising choice for this purpose. In this study, a long-term (2020–2022) field experiment consisting of three treatments, i.e., traditional tillage (TT), deep rotary tillage (DT), and deep vertical rotary tillage (VRT), was carried out in semiarid areas of Loess Plateau, northwest China, to investigate the effects of VRT on soil water storage (SWS), phase crop evapotranspiration (ETc) during the pre- and post-flowering periods, dry matter accumulation, grain yields and the water use efficiency (WUE) of forage maize. The results showed that VRT significantly improved the absorption of soil moisture from deep layers, especially in dry years. During the pre-flowering period of a dry year (2020), VRT decreased SWS by 7.6%–10.0% in the 60–180 cm layer, and by 17.6%–18.5% in the 180–300 cm layer, respectively, compared to DT and TT. As a result, VRT increased ETc during the pre-flowering period by 6.1% and 9.2%, respectively. In wet years (2021 and 2022), VRT increased total ETc by 2.0%–7.9% in 2021, and by 10.1%–14.9% in 2022, respectively. On average, VRT increased the dry matter weight per plant by 1.0%–7.8%, grain yields by 2.4%–38.6%, biomass yields by 3.4%–16.2%, and WUE by 10.1%–30.0%, respectively. Particularly, the benefit of VRT for increasing yields and WUE was more noticeable in dry years. It can be concluded that VRT is a drought-tolerant and yield-boosting tillage technique that is suitable for rain-fed forage maize in semiarid areas of Loess Plateau, northwest China. [ABSTRACT FROM AUTHOR]