Responses of Growth and Yield of Apple–Polygonatum sibiricum Intercropping System to Agronomical Measures and Supplemental Irrigation on the Loess Plateau of China

The competition between species for soil water represents a significant constraint on the growth and productivity of species within agroforestry systems on the Loess Plateau. This study employed field experiments conducted in 2022 and 2023 to elucidate the impact of agronomic measures（straw mulching, film mulching, root barrier treatment and increasing the spacing between crops and trees）and supplemental irrigation（the lower limits of 55%, 70% and 85% of the field's water holding capacity at three key stages of Polygonatum sibiricum） on the growth, yield and water use efficiency of the components of the apple–Polygonatum sibiricum intercropping system. The findings indicated that all agronomic measures resulted in an increase in soil water content within the intercropping system, with film mulching emerging as the most effective approach. Moreover, the application of film mulching markedly enhanced the growth and yield of the components of the intercropping system, thereby establishing it as an optimal agronomic measure for the apple–Polygonatum sibiricum intercropping system. With the exception of water use efficiency, the growth and yield of the components of the intercropping system increased with the greater quantity of supplemental irrigation. In the Loess Plateau region, where precipitation resources are scarce, film mulching was employed in the apple–Polygonatum sibiricum intercropping system. Meanwhile, the lower supplemental irrigation limits for the Polygonatum sibiricum at the flowering–fruiting stage, fruiting–mature stage and seedling–flowering stage were set at 55%, 85% and 70% of the field water holding capacity, respectively. These measures can assist in alleviating interspecies soil water competition in the apple–Polygonatum sibiricum intercropping system, thereby enhancing the growth, yield and water use efficiency of the intercropping system.