Effects of ridge-furrow rainwater harvesting with biochar-soil crust mulching on ridge runoff, soil hydrothermal properties, and sainfoin yield

Ridge-furrow rainwater harvesting (RFRH) with mulch offers farmers a means to address drought, water loss, and soil erosion in arid and semiarid regions. The purpose of this study was to determine a suitable biochar type and optimum ridge width for sainfoin (Onobrychis viciaefolia Scop.) production using the RFRH system with biochar application in the semi-arid regions in China. A field experiment with a completely random block design was conducted during the 2017 sainfoin growing season to (1) estimate runoff coefficient of the RFRH system with three ridge widths (30, 45, and 60 cm) and the same narrow width (60 cm), and mulched with three materials (soil crust, maize straw biochar-soil crust, and cow dung biochar-soil crust) and (2) assess the effects of three ridge widths and three mulching materials on soil water storage, topsoil temperature, as well as fodder yield and water use efficiency (WUE) of the RFRH system planted with sainfoin, and a traditional flat planting (FP) system was used as the control. The results showed that the predicted runoff coefficient for ridge-furrow planting with the ridges mulched with manually compacted soil crust, maize straw biochar-soil crust, and cow dung biochar-soil crust (MCS, MSB, and CMB, respectively) was 29.7%, 26.2%, and 25.1%, respectively, whereas the threshold rainfall to produce runoff was 4.2, 4.6, and 5.1 mm, respectively. The runoff coefficient of ridge, soil water storage, and soil temperature increased with increase in ridge width using the same mulching materials. The RFRH system, especially MSB and CMB treatments, increased soil water storage of the root layer and ridge topsoil (0-25 cm) temperature, and decreased the rate of change of furrow top soil (0-25 cm) temperature. Compared with that of FP, the mean soil water storage (0-200 cm) increased by 25.1, 24.7, and 19.4 mm, on an average, under MCS, MSB, and CMB throughout the sainfoin growth period, respectively; whereas the topsoil temperature increased by 1.4℃, 2.0℃, and 2.0℃, respectively, on an average. For the same mulching material, soil water storage and topsoil temperature increased with increase in ridge width. MCS significantly decreased the actual fodder yield of sainfoin, but MSB and CMB significantly increased the actual fodder yield. Compared with that under FP treatment, the actual fodder yield under MCS with 30, 45, and 60 cm ridge width decreased by 6.5%, 12.1%, and 13.8%, respectively. Whereas, the actual fodder yield under MSB with 30, 45, and 60 cm ridge width increased by 19.7%, 24.4%, and 22.5%, and that under CMB increased by 8.0%, 8.9%, and 6.8%, respectively. MSB and CMB significantly increased WUE of sainfoin. Compared with FP, MSB and CMB increased WUE by 6.8-9.7 and 4.4-4.8 kg·hm^-2·mm^-1, respectively. The ridge width had no significant effect on the actual fodder yield and WUE with the same mulching materials. When the ridge width (furrow width was 60 cm) was 49 cm for MSB and 41 cm for CMB, the forage yield reached the maximum. The actual fodder yield and WUE of sainfoin under MSB were significantly higher than those under CMB, which were significantly higher than those under MCS. In summary, RFRH with biochar-soil crust mulching has beneficial effects on soil water storage and yield of sainfoin in the region, especially ridges with maize straw biochar-soil crust mulching.