Deep-rooted perennials and vertical hydrological connectivity: Mitigating cropland waterlogging and enhancing resilience to extreme rainfall

To study the effects of annual cropland conversion to perennial forage cropland on infiltration rates and water dynamics, we conducted infiltration tests in August 2024 across the three treatments. A total cumulative infiltration of 1,000 mm was applied in each test using a single-ring infiltrometer, with three replicate measurements per treatment. The infiltrometer, with a diameter of 35 cm, was inserted vertically into the soil to a depth of 10 cm after removing surface vegetation and litter. Tests were conducted on flat, representative areas, and care was taken to ensure the ring remained level. Tap water was added in increments of 50 mm (4.81 L per addition), and the time required for each increment to infiltrate was recorded. Each test was concluded once cumulative infiltration reached 1,000 mm, from which the total infiltration time (IT) was determined. After the infiltration experiments concluded (cumulative infiltration = 1000 mm), the ring was removed and the area immediately covered with a shade net to minimize evaporation and allow water redistribution within the soil profile. Samples for soil water content were collected 24 hours later, a standard interval that permits redistribution of the infiltrated water while minimizing evaporative losses and deep percolation beyond the target profile (Dane and Hopmans, 2002). Samples were collected at the center of the infiltration test point with a 4-cm-diameter soil auger at 10-cm intervals down to 400 cm. To determine initial soil water content, the same procedure was applied prior to infiltration, with samples collected 3 m from the infiltration test point. Gravimetric water content (g g-1) was then obtained in the laboratory using the standard oven-drying method (105°C for 24 hours). One week after the infiltration experiments, a vertical soil profile was excavated along the centerline of the infiltration point and soil samples were collected at 10-cm intervals from 0 to 100 cm. At each depth interval, two adjacent samples were collected: one for assessing root distribution and the other for soil physical and hydraulic properties. Root distribution was obtained following Bohm (1979). Soil monoliths (10 x 15 x 15 cm) were carefully excavated from each depth interval. Cylinders weights were subtracted from the measurements. These values were then used to calculate dry bulk density (BD), total porosity (TP), capillary porosity (CP), and non-capillary porosity (NCP) were calculated.为探究一年生农田转换为多年生饲草农田对土壤入渗速率及水分动态的影响，我们于2024年8月针对三种试验处理开展了入渗试验。本试验采用单环入渗仪（single-ring infiltrometer），每组处理设置三次重复测量，每次试验均施加累计入渗量1000 mm的水量。该单环入渗仪直径为35 cm，在清除地表植被与枯落物后，垂直插入土壤10 cm深度。试验选取平坦且具有代表性的区域开展，并确保入渗环始终保持水平。采用增量投加方式添加自来水，每次添加量为50 mm（单次加水量为4.81 L），并记录每一批次增量水分完全入渗所需的时长。当累计入渗量达到1000 mm时结束单次试验，由此计算得到总入渗时间（total infiltration time, IT）。入渗试验结束（累计入渗量为1000 mm）后，移除入渗环，随即用遮阳网覆盖试验区域，以减少蒸发损失并使水分在土壤剖面中充分重新分布。24小时后采集土壤含水率样品——该间隔时长为行业公认标准，可确保入渗水分充分完成重新分布，同时将蒸发损失与目标剖面外的深层渗漏降至最低（Dane与Hopmans，2002）。样品采集于入渗试验点的中心位置，采用直径4 cm的土壤取样钻（soil auger），以10 cm为间隔向下采集至400 cm深度。为测定初始土壤含水率，我们在入渗试验前开展了相同的取样流程，采样点距离入渗试验点3 m。随后在实验室采用标准烘干法（oven-drying method），于105℃下烘干24小时，测定土壤重量含水率（gravimetric water content, g·g⁻¹）。入渗试验结束一周后，沿入渗点中心线开挖垂直土壤剖面，以10 cm为间隔从0至100 cm深度采集土壤样品。每个深度间隔采集两份相邻样品：一份用于分析根系分布，另一份用于测定土壤物理及水力特性。根系分布的测定参考Bohm（1979）的标准方法。从每个深度间隔小心采集土壤柱样（10×15×15 cm），通过扣除取样环刀的重量得到干重，进而计算得到干容重（dry bulk density, BD）、总孔隙度（total porosity, TP）、毛管孔隙度（capillary porosity, CP）与非毛管孔隙度（non-capillary porosity, NCP）。