Intercropping systems reduce ineffective evaporation between trees but also intensify interspecific competition and reduce productivity. To improve the water-use efficiency and the economic benefits of an intercropping system on the Loess Plateau, China, where rainfall is limited and evaporation intense, an apple–soybean intercropping system with micro-irrigation water control was adopted to analyze the soil water, root density, water-use efficiency, yield, and economic benefits of intercropping under different micro-irrigation methods. Subsurface seepage irrigation, bubbler irrigation, and drip irrigation under mulching were used with irrigation upper limit levels of three maximum irrigation levels [60% (W1), 75% (W2), and 90% (W3) of field capacity (FC)]. Rainwater harvesting from ridges and furrows (GL) without irrigation was the control. Bubbler irrigation increased the soil water content, optimized the vertical soil water distribution, and promoted root growth. Except for the control treatment (GL), the other micro-irrigation treatments increased with the irrigation amount, but the water-use efficiency decreased. Drip irrigation under mulch combined with W2 (75% Fc) irrigation could obtain the maximum intercropping yield, which was increased by 71.1% compared with the GL treatment. Drip irrigation under a mulch combined with W2 produced the maximum intercropping yield; the economic benefits were higher under drip irrigation with mulching combined with W1; and all three micro-irrigation methods combined with W2 improved the economic benefits by 52.1–115.5% compared to GL. Drip irrigation under mulching or bubbler irrigation combined with W2 should be used when there are sufficient water resources, but drip irrigation under a mulch combined with W1 when there is a water shortage.

In this study, a typical apple–soybean intercropping system was used to analyze the effects of different soil water and heat regulation modes on the spatial distribution of the soil water content (SWC), photosynthetic physiological characteristics, and growth. Three maximum irrigation levels [50% (W1), 65% (W2), and 80% (W3) of field capacity (FC)] and two mulching intervals [from seedling to podding stage (M1) and during the full stage (M2) of soybeans] were tested. The results showed that the SWC of W3M2 was the highest, while the W2M1 and W1M2 treatments used more deep soil water. Irrigation increased the chlorophyll content, net photosynthesis, and transpiration rate of leaves in the agroforestry system. In addition, the net photosynthetic rate of leaves under the W2 irrigation level increased after mulch removal in the later growth stage. At W1 and W2 irrigation levels, the soybean yield of half-stage mulching was 0.85–15.49% higher than that of full-stage mulching. Multiple regression analysis showed that grain yield under the W3M2 treatment reached the maximum value of the fitting equation. The photosynthetic rate, water use efficiency, and grain yield under W2M1 reached 71–86% of the maximum value of the fitting equation, with the largest soil plant analysis development value. To effectively alleviate water competition in the apple–soybean intercropping system, our results suggest adoption of the 80% FC upper irrigation limit (W3) combined with soybean M2 treatment in young apple trees–soybean intercropping system during water abundant years. In addition, adoption of the 65% FC upper irrigation limit (W2) combined with the soybean M1 treatment in water deficit years could effectively improve soil water, heat environment, and promote growth.

Uneven soil moisture and nutrient distribution before and after intercropping limits apple cropping system productivity in the western Shanxi–Loess Plateau area. To address this issue, a field trial was conducted between 2020 and 2021 to study the effects of different water and fertilizer management practices on soil moisture, nutrients, and root distribution, as well as the overall effectiveness of the apple–maize and apple–soybean intercropping systems during crop replacement. The experiment involved two irrigation methods: drip (D) and flood (M) irrigation. Three irrigation levels included rain-fed without irrigation (W0), and 50% (W1) and 80% (W2) of field capacity (Fc). Three fertilizer treatments included no additional fertilizer application (F0), 375 kg∙hm⁻² (F1), and 750 kg∙hm⁻² (F2), in addition to a control (CK) without irrigation or fertilization. The soil water content (SWC) decreased after the crop replacement. Additionally, nitrate nitrogen (NN), ammonium nitrogen (AN), and organic matter (OM) content levels in all treatments increased, whereas total phosphorus (TP) content decreased. The soil layer with crop roots moved downward after crop replacement, and partial fertilizer productivity (PFP), irrigation water use efficiency (IWUE), and water use efficiency (WUE) were decreased under both irrigation treatments. Principal component analysis showed that the W2F2 treatment had the highest benefit from crop combination across both irrigation treatments during the crop replacement period. According to our results, to optimize the benefits of apple-crop intercropping, drip irrigation with complete water supply and flood irrigation with incomplete water supply are recommended during crop replacement. In addition, an upper irrigation limit of 80% Fc with 750 kg∙hm⁻² fertilization is recommended for optimal water and fertilizer regulation.

Uneven soil moisture and nutrient distribution before and after intercropping limits apple cropping system productivity in the western Shanxi loess area. To address the problem, a field experiment was conducted between 2020 and 2021 to investigate the effects of different water and fertilizer management practices on soil moisture, nutrients, root distribution, and overall benefits of the intercropping system during the crop replacement period. The experimental set up included three factors: irrigation method, irrigation level, and fertilizer application; irrigation methods included drip (D) and flood (M) irrigation; irrigation levels included rain-fed without irrigation (W0), 50% of the field water holding capacity (Fc)-W1, and 80% of the field water holding capacity (Fc)-W2; fertilizer treatments included F0 (no additional fertilizer application), F1 (N 206.2 kg∙hm-2 + P2O5 84.4 kg∙hm-2 + K2O 84.4 kg∙hm-2), F2 (N 412.4 kg∙hm-2 + P2O5 168.8 kg∙hm-2 + K2O 168.8 kg∙hm-2), and control (CK) without irrigation and fertilization, for a total of 15 treatments. According to the results, soil water content (SWC) decreased after the crop replacement. Besides, nitrate nitrogen (NN), ammonium nitrogen (AN), and organic matter (OM) contents in all treatments increased, whereas total phosphorus (TP) content decreased. The main soil aggregate layer with crop roots shifted downwards (from the 0–40 cm soil layer before crop replacement to the 0–60 cm soil layer) after crop replacement, and partial fertilizer productivity (PFP), irrigation water use efficiency (IWUE), and water use efficiency (WUE) under both irrigation treatments were decreased. Principal component analysis showed that the W2F2 treatment had the highest combined benefits both irrigation treatments during the crop replacement period. Structural equation modeling showed that apple tree and maize RLDs had no significant effects on water use (ET) and WUE before crop replacement. Apple tree and soybean RLDs had significant positive correlations with ET and significant negative correlations with WUE after crop replacement. According to our results, to optimize the benefits of apple-crop intercropping, drip irrigation with complete water supply and flood irrigation with incomplete water supply are recommended during crop replacement. In addition, an upper irrigation limit of 80% of the field water holding capacity and a fertilizer application rate of N 412.4 kg∙hm-2 + P2O5 168.8 kg∙hm-2 + K2O 168.8 kg∙hm-2 are recommended for optimal water and fertilizer regulation.