Understory mowing controls soil drying in a rainfed jujube agroforestry system in the Loess Plateau

The widely adopted practice of clean-cultivation in rainfed orchards in the Loess Plateau has led to serious soil erosion and degradation problems. Agroforestry is a promising management practice for solving these problems, but may reduce available soil water. Thus, reasonable soil and water management strategies should be developed for agroforestry systems in this region. The objective of this study was to determine whether adopting proper mowing management of the understory intercrop limited soil drying in a rainfed jujube (Ziziphus jujuba Mill.) orchard in this region. Various mowing intensities (3-, 6-, 9-cm stubble height and unmowed treatments) were imposed on three intercrop species: bluegrass (Poa pratensis L.), white clover (Trifolium repens L.), and hairy vetch (Vicia villosa Roth) to investigate and compare their root characteristics and soil moisture responses to mowing under greenhouse and field conditions. Based on the results, the most promising intercrop species and mowing intensity to be used in a jujube orchard were selected for field validation. The results showed that mowing effectively regulated intercrop root amount and distribution, as well as associated soil moisture conditions. However, the sensitivities of root characteristics and soil moisture to mowing and growth environment were species-specific. Bluegrass mowed to a 3-cm stubble height produced the minimum root amount, the shallowest root depth, and the greatest soil water content. When this treatment was applied to a rainfed jujube orchard during the 2015 and 2016 growing seasons, average soil moisture in the 0–300 cm soil layer was essentially unaffected, while fruit yield was increased. Consequently, bluegrass mowed to a stubble height of 3 cm when intercropped with jujube trees in the Loess plateau is a feasible practice to increase jujube yield and avoid extra soil drying.