4.3. Implications
Since the initiation of the Grain for Green project in 1999, extensive commercial plantations of jujube, apple (Malus domestica ), walnut (Juglans regia ), and peach (Prunus persica ), among others, have been planted on the Loess Plateau, with the aim of delivering ecological and economic benefits (Gao et al., 2014). For example, the area of planted apple trees reached 130 million ha by 2017 (Gao et al., under review). On the Loess Plateau, these commercial plantations are primarily run by smallholder farmers. Because of the complex topography and high cost of irrigation, most of these plantations are rainfed (Gao et al., 2018b). Therefore, efficient use of rainwater and improved SWS are critical to their success. Our results indicate that, compared to traditional hillslopes and terraces alone, the combination of terracing and mulching clearly increases SWS, enhances deep-layer water use and transpiration, and results in higher mid-day leaf water potential, particularly during drought periods. Therefore, the combination of terraces and mulches is strongly recommended for use in commercial plantations on the Loess Plateau, and potentially also in drylands worldwide, thus helping to deliver Sustainable Development Goals (United Nations, 2015).