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The shortage of and intense competition for water and light are the main factors restricting the productivity of agroforestry systems in the Loess Plateau of western Shanxi, China. The combination of soil mulch and irrigation in agroforestry systems can regulate the interspecific relationships and increase the productivity of the component crops. However, the effects of mulch and irrigation regimes on the photosynthetic physiological characteristics of the agroforestry system and its synergistic mechanisms are still unclear. A 3-year experiment with two factors, mulch and irrigation, was conducted to investigate the effects of different mulch practices and irrigation levels on the photosynthetic characteristics, growth indices, and interspecific relationships of a fruit tree-crop intercropping system. An apple–soybean intercropping system was selected as the research object, and two mulch types [straw mulch (M1) and plastic mulch (M2)] and four maximum irrigation levels [no irrigation (W0), 55% (W1), 70% (W2), and 85% (W3) field capacity (Fc)] were tested. No mulch together with no irrigation was the control treatment (CK). The results showed that there was no photosynthetic siesta phenomenon in the intercropping system, and the daily variations of the net photosynthetic rate (Pn) and transpiration rate (Tr) were unimodal. The mean values for Pn, Tr, and leaf photosynthetic efficiency (PUE) of the apple and soybean under the M2 treatment were generally higher than under the M1 treatment, whereas Tr and PUE increased as the amount of irrigation increased. In 2017–2018, the maximum mean Pn values for both apple and soybean were observed under the M2W2 treatment, whereas in 2019, they were observed under the M2W3 treatment. The Pn, Tr, and leaf intrinsic water use efficiency (WUEi) of soybean correlated positively with the distance from the trees, whereas PUE correlated negatively with it. Mulch and water replenishment increased apple shoot growth and the height, leaf area index, and yield of soybean, especially under plastic mulch. A principal components analysis found that the M2W2 treatment had the highest comprehensive benefits in 2017–2018, whereas in 2019, the highest were achieved with the M2W3 treatment. Therefore, to optimize the photosynthetic efficiency and yield of the apple–soybean intercropping system in the loess region of western Shanxi, we suggest a combination of plastic mulch and maximum irrigation of 70% Fc in normal years, but maximum irrigation should be increased to 85% Fc in dry years. • Both mulch and irrigation enhanced photosynthesis and yield in apple-soybean intercropping system. • The photosynthesis parameters under plastic mulch was greater than those under straw mulch. • Plastic mulch and 70–85% Fc irrigation was the most efficient regimes for the apple-soybean intercropping system. [ABSTRACT FROM AUTHOR]

Soil water and nutrients are the main factors that restrict the stable development of alley cropping systems in the Loess Plateau of west Shanxi, China. Field experiments were conducted during 2014–2016 to investigate the effects of water and fertilizer coupling regulation on soil water, nutrient distribution and their use efficiencies in a typical apple–maize alley cropping system in the area. There were three upper limits for irrigation according to appropriate ranges of soil moisture for apple and maize, 50% (W1), 65% (W2) and 85% (W3) of field capacity (Fc) for the 0–60 cm soil layer, coupled with three nitrogen/phosphorus/potassium compound fertilizer levels of F1 (289.0/118.0/118.0 kg∙ha−1), F2 (421.4/168.8/168.8 kg∙ha−1), and F3 (537.0/219.0/219.0 kg∙ha−1) and a CK (rain fed, no irrigation or fertilizer) as a control, making a total of 10 treatments. The results indicated that the horizontal and vertical soil water content (SWC) increased with distance from the tree row and with soil depth, respectively. The SWC near the maize belts was greater than near the tree line, and this was reversed with the increase of intercropping years. In the horizontal direction, the soil nutrient content (SNC) for each indicator increased with distance from the tree row, with the maximum value occurring at 2.5 m. In the vertical direction, SNC decreased with soil depth, with the maximum value at 0–20 cm. The 85% Fc combined with 70% empirical fertilizer application amount resulted in the maximum grain yield and partial factor productivity (PFP). Irrigation water use efficiency (IWUE) was highest for the F1 level. Multivariate and spatial analyses showed that a range of 50–65% Fc combined with 70% empirical fertilizer application was suitable for optimal irrigation and fertilization management of this alley cropping system considering the integrated benefits of maize yield, IWUE and PFP. • With the increasing intercropping years, the apple trees showed soil water and nutrient advantages. • Excessive irrigation and fertilization can cause soil nutrients leaching and reduce the water and fertilizer use efficiency. • 50%−65% Fc combined with 70% empirical fertilizer application amount was most optimal management. [ABSTRACT FROM AUTHOR]

Water scarcity seriously hinders the sustainable development of the fruit tree–crops intercropping system in the Loess Gully Area of western Shanxi. The combination of mulch measures and appropriate irrigation would help to maintain soil moisture and improve crop yield and water use efficiency (WUE). This study investigated the combined effects of mulch and irrigation on soil water and root distribution, yield, and water use of an apple–soybean intercropping system. A three-year field trial was performed with two factors: two types of mulch, namely straw mulch (M1), and plastic mulch (M2), and three levels of maximum irrigation (55%, 70%, or 85% of field capacity [Fc]), which were designated W1, W2, and W3, respectively. Three groups of non-irrigation controls i.e., CK0 (no mulch), CK1 (straw mulch), and CK2 (plastic mulch) were also included. These results indicated that the soil water contents (SWC) in each treatment initially decreased and then increased with increasing distance from the tree, whereas it increased gradually with depth. The SWCs in various sampling points under straw mulch was generally higher than under plastic mulch. The root length density (RLD) of apple tree decreased with increasing distance from the tree in the horizontal direction, while the opposite trend was observed for soybean. The RLD of both apple tree and soybean in the soil layer (0–60 cm) under plastic mulch was higher than that under straw mulch, and increased with increased irrigation level. The underground interspecific competition intensity index (UICII) of the apple–soybean intercropping system under straw mulch was higher than that under plastic mulch, and increased with the increased irrigation amount. Water consumption, soybean yield, and WUE under plastic mulch were significantly higher than under straw mulch. The results of this study suggested that the combination of plastic mulch and irrigation water supplied at 70–85% Fc could effectively increase the yield and WUE of the apple–soybean intercropping system. • Mulch and irrigation reduced underground competition in apple-soybean intercropping system. • The soil water content under straw mulch was greater than that under plastic mulch. • Plastic mulch significantly improved water use efficiency of apple-soybean intercropping system. • Plastic mulch and 70–85% Fc irrigation was the most efficient regimes. [ABSTRACT FROM AUTHOR]