Temporal variations in rill erosion resistance following incorporated wheat straw returning combined with nitrogen and polyphenols

The widely implemented wheat straw incorporation returning combined with nitrogen fertilizer and newly-developed secondary plant metabolites such as polyphenol, could result in variations of rill erosion resistance, and then soil detachment and channel scour. However, the variation pattern and its key influencing factorsremain unclear. Taking a silt loam soil as the research object, this study used the orthogonal table of L 9 (3 4 ) to arrange four influencing factors at three levels: straw length (2, 5, 8 cm), straw returning amount (2000, 4000, 8000 kg h m −2 ), nitrogen amount (100, 140, 180 kg hm −2 ), and polyphenol amount (0, 40, 80 kg hm −2 ). Rill erodibility ( kd ) and soil critical shear stress ( τc ), representing the soil resistance to rill erosion, were measured twice by submerged jet equipment in August 2020 and 2021. The results presented significant temporal variations in kd and τc with changes in straw decomposition and soil properties after straw incorporation. Compared with the results on day 60 following straw incorporation, kd and τc decreased by 57.07% and 25.11% on day 425, respectively. On day 425, the straw length, straw returning amount, and nitrogen amount had significant effects on kd ( P  < 0.05), with the contributions of 7.97%, 42.06%, and 7.62%. Conversely, the straw returning amount and polyphenol amount had significant effects on τc, with respective contributions of 50.88% and 11.24%. The variation of kd and τc could be linearly fitted by the soil aggregate greater than 0.25 mm, with R2 values of 0.71 and 0.87, respectively, which could be used to estimate rill channel scour depth in the Soil and Water Assessment Tool in the absence of measured data on soil resistance to rill erosion.