Effects of Crop–Hedgerow Intercropping on the Soil Physicochemical Properties and Crop Yield on Sloping Cultivated Lands in a Purple Soil of Southwestern China

Crop–hedgerow intercropping systems are important agroforestry systems for preventing soil degradation and soil nutrient losses on sloping cultivated land in the Three Gorges Reservoir (TGR) area of China. However, the mechanism by which hedgerow spatial layouts and the planting patterns affect soil nutrients and crop yields is still uncertain. A two-year field experiment was performed on a 10° slope to investigate the effects of slope position and different crop–hedgerow intercropping systems on soil physicochemical properties and crop yields. The treatments were a two-belt mulberry contour hedgerow (TM), a two-belt compound mulberry–vetiver hedgerow (TCMV), a two-belt compound mulberry–alfalfa hedgerow (TCMA), a seven-year-old two-belt mulberry contour hedgerow (7YTM), a seven-year-old mulberry border hedgerow (7YBM), a seven-year-old pure mulberry (7YPM), and a control treatment (CT, no hedgerows). In all treatments, except 7YPM, there was a significant (p < 0.05) increase in crop yield, clay content, soil total nitrogen (STN), acid-hydrolyzable nitrogen (AHN), and soil organic carbon (SOC) with declining slope position, whereas soil bulk density (BD), sand content, and soil pH showed the opposite trend. In TM, TCMV, TCMA, and 7YTM, the mustard yields and soil properties were better than those in CT, and there was no significant (p > 0.05) difference in mustard yield or soil properties between the upper-middle and lower-middle slope positions. Compared with CT, TCMV, and TCMA increased mustard yields by 8.28% and 9.86%, respectively, while 7YTM, 7YBM, and 7YPM reduced mustard yields by 7.69%, 17.69%, and 29.73%, respectively. TCMV and TCMA were confirmed to be viable intercropping systems for significantly reducing nutrient losses, improving soil quality, and changing soil nutrient distributions to maintain optimum crop yields on sloping lands.

Mechanized and Optimized Configuration Pattern of Crop-Mulberry Systems for Controlling Agricultural Non-Point Source Pollution on Sloping Farmland in the Three Gorges Reservoir Area, China

High-intensity utilization of sloping farmland causes serious soil erosion and agricultural non-point source pollution (AGNSP) in the Three Gorges Reservoir Area (TGRA). Crop-mulberry systems are important agroforestry systems for controlling soil, water, and nutrient losses. However, there are many different mulberry hedgerow planting patterns in the TGRA. In this study, soil structure, nutrient buildup, and runoff nutrient loss were observed in field runoff plots with five configurations: P1 (two longitudinal mulberry hedgerows), P2 (two mulberry contour hedgerows), P3 (three mulberry contour hedgerows), P4 (mulberry hedgerow border), and P5 (mulberry hedgerow border and one mulberry contour hedgerow), as well as a control (CT; no mulberry hedgerows). P1 had the smallest percentage of aggregate destruction (18.8%) and largest mean weight diameter (4.48 mm). P5 led to the greatest accumulation of ammonium nitrogen (NH4+–N) and total phosphorus (TP) (13.4 kg ha−1 and 1444.5 kg ha−1 on average, respectively), while P4 led to the greatest accumulation of available phosphorus (AP), nitrate nitrogen (NO3−–N), and total nitrogen (TN) (114.0, 14.9, and 1694.1 kg ha−1, respectively). P5 was best at preventing soil erosion, with the smallest average annual runoff and sediment loss of 112.2 m3 ha−1 and 0.06 t ha−1, respectively, which were over 72.4% and 87.4% lower than those in CT, respectively. P5 and P4 intercepted the most N in runoff, with average NH4+–N, NO3−–N, particulate N, and TN losses of approximately 0.09, 0.07, 0.41, and 0.58 kg ha−1, respectively, which were 49.7%, 76.2%, 71.3%, and 69.9% lower than those in CT, respectively. P5 intercepted the most P in runoff, with average TP and total dissolved phosphorus (TDP) losses of 0.09 and 0.04 kg ha−1, respectively, which were 77.5% and 70.4% lower than those in CT, respectively. Therefore, the pattern with one mulberry hedgerow border and one mulberry contour hedgerow (P5) best controlled AGNSP, followed by that with only a mulberry hedgerow border (P4).