Rainwater harvesting capacity of soils subjected to reservoir tillage during rainfall on the Loess Plateau of China

Soil rainwater harvesting (SRWH) is an important process in rainfed farming areas. Improving the capacity for SRWH via tillage is essential in many parts of the world. In recent years, reservoir tillage (RT) has attracted attention because it was said that RT contributes to SRWH. The objectives of this study were to measure the cumulative soil-harvested rainwater (SHR) of slopes subjected to RT and to evaluate the contribution of RT to SRWH under different rainfall conditions. A smooth surface (SS) served as a control surface. Three slope degrees (5 degrees, 15 degrees and 25 degrees) were subjected to low and heavy (60 and 120 min/h) and long-term rainfall (90 min). The results showed that the cumulative SHR decreased to different extents under different rainfall intensities as the slope degree increased. On the gentle slope (5 degrees) and under low rainfall intensity (60 mm/h), no significant differences in cumulative SHR were detected between the RT and SS treatments, whereas significant differences in cumulative SHR were detected between them on the steep slopes (15 degrees and 25 degrees) and under high rainfall intensity (120 mm/h). The differences in cumulative SHR among the different conditions occurred because the contribution of RT to SRWH varied as the soil surface properties changed (especially as surface depression storage decreased due to sediment deposition) under the conditions of long-term rainfall. For example, on the 5 degrees slope at a rainfall intensity of 120 mm/h, the contribution of RT to SRWH was 18.58% during the 0-30-min rainfall stage but -14.84% during the 60-90-min stage, resulting in nearly equal cumulative SHR values between the RT slope and the SS slope. Our results suggest that RT is not necessary contribute to SRWH in all cases.