Integrating mulching and supplementary irrigation for soil environment improvements in apple orchards of northwest China

Abstract: Mulching and supplementary irrigation are commonly used water-saving techniques ensuring agricultural sustainability in drylands of northwest China. However, the effects of the combination of mulching and supplementary irrigation on the soil environment, and the growth of apple trees remain unclear. Field experiments were conducted in 2023 to evaluate the effects of the combination of mulching and supplementary irrigation on the soil water and heat, and the growth of apple trees. In the experiments, one mulching method (corn straw mulching, SM), two types of drip irrigation, which included above-ground ring drip irrigation (M1) and above-ground two-row drip irrigation (M2), were used. Additionally, three irrigation levels of 100% (W1), 75% (W2), and 50% (W3) of full irrigation (referred to as full, moderate deficit, and severe deficit irrigation, respectively) were used. The results showed that SM significantly increased the soil water content (SWC), especially in the early stage of the growth period. SM significantly reduced and stabilized the soil temperature during the whole growth season, while M1 and M2 had no significant effect on the soil temperature. Both mulching and drip irrigation significantly increased the net photosynthetic rate (Pn) of leaves. Supplementary irrigation had no significant effect on shoot length, but increased shoot diameter. The evapotranspiration of various stages on apple trees was in the following descending order: fruit expansion stage (III), bud development and flowering stage (I), leaf expansion stage (II), and fruit maturing stage (IV). Therefore, SM has the potential to increase apple yields in the Loess Plateau by improving the soil environment and regulating the growth and physiology of apple trees.