Soil properties of apple orchards on China's Loess Plateau

There are many apple orchards on the Loess Plateau because of their economic value and aggressive expansion is planned. However, little is known about their ecological impact in deep soil water, soil organic carbon (SOC) and soil aggregation. An accurate evaluation of the soil properties of apple orchards is crucial to ensure the establishment of sustainable ecosystems. We, therefore, measured the soil water content variation in deep layers (200-800 cm), SOC content and density (0-800 cm) and, soil aggregate stability (0-40 cm) in apple (Malus pumila) orchards, black locust (Robinia pesudoacacia) and korshinsk peashrub (Caragana korshinskii). We found that (1) there was generally less soil water in deep soil under apple orchards (13.29%), black locust (12.4%) and korshinsk peashrub (13.46%) than under arable land (18.35%) (p < 0.05). This implies that plantations caused intense reductions in soil water compared with arable land, leading to severe soil desiccation. (2) Apple orchards (1.85 to 5.49 g kg^-1) had significantly (p < 0.05) lower SOC density (SOCD) than ecological plantations (2.15 to 8.95 g kg^-1). It suggests that apple orchards have a low value for SOC sequestration because their clean cultivation management increases the risk of SOC loss by soil erosion. (3) soil aggregate stability (mean weight diameter, MWD) in apple orchards (0.26-0.63 mm) was significantly (p < 0.05) lower than under black locust (0.63-2.97 mm) and korshinsk peashrub (0.72-2.13 mm) plantations in the 0-40 cm layers, which means that apple orchards have low anti-erodibility. Our results suggest apple orchards and ecological plantations both consumed large amounts of deep soil water, but the ecological benefits (e.g., SOC sequestration, soil and water conservation) delivered by ecological plantations are much higher than those of apple orchards. In the interest of sustainable development in the region, apple cultivation should be undertaken with caution, especially in semiarid regions.