Spatial distribution of soil water, plant roots, and water use pattern under different drip fertigation regimes in an apple-soybean intercropping system on the Loess Plateau, China

The irrational utilization of water resources restricts the sustainable development of tree-crop intercropping in the Loess region. Drip fertigation was applied for two years in an intercropping system to save water resources, and improve water use efficiency (WUE) and crop yield. The spatial distribution of soil water , plant roots, and water use pattern were investigated in a drip fertigated intercropping system. A two-factor randomized block design was adopted. Four irrigation levels: 60% (W1), 70% (W2), 80% (W3), and 90% (W4) of field capacity (Fc), together with three nitrogen fertilization treatments [59.40 (F1), 92.00 (F2), and 124.32 kg ha –1 (F3)], were set up with a blank control (CK), which was rain-fed with base fertilizer applied before sowing. The soil water content (SWC) distribution had a “U” shape in the horizontal direction, and the vertical water competition area moved downward as the intercropping year increased. The soybean root length density (RLD) increased as the distance from the tree row increased, but apple showed the reverse trend. The overlap between apple and soybean roots generally decreased as the distance from the tree row increased, but the vertical overlap of roots extended from 0–40 cm (2018) to 0–60 cm (2019). The interspecific competition increased with the increase in intercropping years, resulting in a downward shift of the competition area. Water consumption in 2018 and 2019 increased as the irrigation level rose. The SWC, RLD, soybean yield, and WUE of W3F2 were the highest among the treatments. Excessive irrigation can lead to vigorous vegetative growth , but reduced yields. The negative effects of intense interspecific competition were relieved under drip fertigation. The results suggested that drip irrigation at 80% Fc combined with 92 kg ha –1 N fertilization can improve the yield and WUE of the apple-soybean system on the Loess Plateau . • The negative effects of intense interspecific competition were relieved under drip fertigation. • Excessive irrigation can lead to vigorous vegetative growth, but reduced yields in tree-crop system. • 80% Fc maximum irrigation combined with 92 kg ha −1 N fertilization can improve the yield and WUE of the apple-soybean system through drip fertigation on the Loess Plateau.