Efficacy of earthworm casts on sediment and nitrate loss with runoff in the Chinese Loess Plateau

Abstract

The erosion of sediment and nutrients under rainfall conditions aggravated the degradation of soil quality in sloping farmland. It is very important to comprehensively control the sediment and nutrient loss of sloping farmland and improve the soil fertility of barren sloping farmland caused by soil erosion to improve the plant growth environment in the Loess Plateau of China. However, there is no research to combine the control of soil, water, and nutrient loss with the improvement of soil fertility. To address this issue, earthworm casts (ECs), an excellent organic soil amendment, was applied to the soil (silty loam). Ten rainfall simulation experiments were conducted in a 1.0 m × 1.0 m plot with two application methods (mixed and layered applications) and five application amounts (i.e., 0, 200, 400, 600, and 800 g/m2), and simulated rainfall for 1 h at a rate of 60 mm/h. The main results indicated that the ECs application significantly delayed the time of runoff initiation, reduced unit discharge and sediment yield rate in the early stage. The nitrate nitrogen concentration in runoff could be significantly reduced with the layered application method. The equivalent model of convection was more suitable for simulating nutrient transfer with runoff, and the effective mixing depth decreased with increased the ECs amounts. The ECs application increased the water content and nitrate nitrogen concentration of the soil profile from a depth of 0–20 cm and provided a suitable environment for vegetation growth. Runoff decreased by 18.16–33.47%, sediment decreased by 28.17–87.24%, and nitrate nitrogen loss in runoff decreased by 36.99–51.76% with the layered application. The layered application of ECs with 800 g/m2 had the significant regulation on runoff, sediment yield, and nitrate nitrogen loss. In conclusion, ECs can effectively improve the water erosion resistance of the soil, and enhance the water holding capacity and fertilizer retention capacity of the soil. The layered application of ECs can effectively control nitrogen loss with runoff. In the long run, ECs can provide sufficient nutrient sources for plant growth, improve regional vegetation carrying capacity, and fundamentally solve the problem of soil and water loss and soil degradation of bare slope farmland in the Loess Plateau of China.