Effects of Incorporated Straw Length on Runoff and Sediment Characteristics of a Cultivated Black Soil

Straw incorporation is a tillage practice that has been increasingly adopted to sustain soil quality and combat soil erosion in the black soil region of northeast China. Most of the previous studies in this region focused on the impact of incorporation rate, yet the effects of straw length on runoff and sediment characteristics there remain obscure. In this study, maize straw segments of four different lengths (2, 5, 10, 20 cm) were incorporated at a constant rate of 6 t hm⁻² into the plow layer of a cultivated black soil, and a bare black soil without straw application was used as the control (CK). Simulating rainfalls at two intensities (60, 90 mm h⁻¹) and two slopes (3°, 6°), straw incorporation was found to generally delay runoff generation, reduce surface runoff, decelerate surface flow, and impair soil erosion compared to CK. However, the runoff and sediment characteristics responded differently to straw length (SL). As SL increased, the runoff initiation time increased exponentially, the total runoff depth (RD) decreased linearly, but the mean flow velocity initially decreased and then increased. The mean sediment concentration (SC) also exhibited decreasing-then-increasing trends with SL except under the 90 mm h⁻¹ rainfall intensity and 6° slope combination (R90-S6). The relationships of the total sediment yield (SY) with SL basically followed those of SC, which were significantly fitted by the quadratic functions (p < 0.05) and the optimal SL corresponding to the least SY was estimated at ~12 cm. The only exception was spotted under R90-S6 presenting relatively consistent SCs, where similar to RD, SY exhibited a linearly decreasing trend with SL. In this case, the longest straw segments of 20 cm under investigation were believed optimal. These findings demonstrate the critical role of straw length and reveal its varying effects on runoff and sediment characteristics, and hold practical implications for agricultural management on local sloping farmlands.