Quantifying the Impact of Winter Cover Crops on Sediment Export in Small Agricultural Watersheds and Beyond.

Agricultural land use increases the potential for soil erosion when the absence of vegetative cover during the fallow period makes fields vulnerable to runoff. Soil erosion can decrease crop yields and increase sedimentation in downstream water bodies. Agricultural conservation practices, such as the planting of winter cover crops, may protect soils and reduce erosion. To quantify the effect of cover crop use on field- and watershed-scale sediment export, we measured turbidity from tile drains and monitored continuous turbidity at the outlets of two agricultural watersheds in Indiana, USA, over seven water years (Oct 2016-Oct 2022). The watersheds differed in cover crop coverage: Shatto Ditch Watershed (23-68% coverage) and Kirkpatrick Ditch Watershed (8-30% coverage). We related turbidity to total suspended solids (TSS) using grab samples, and generated a record of daily TSS loads. We found that, on average, TSS losses from tiles draining fields with cover crops were 26% lower than fields without cover crops at Shatto, and 65% lower at Kirkpatrick (paired Wilcoxon signed-rank test; p < 0.001 for both watersheds). Average annual TSS yield from Shatto (159 kg/ha/yr) was 30% less than Kirkpatrick (226 kg/ha/yr). We also explored how TSS yields in these two small agricultural watersheds compared to TSS yields in river basins in the state of Indiana, and found that Kirkpatrick yields were significantly higher than the three major basins (ANOVA; p < 0.05), but Shatto TSS yields were not (ANOVA; p > 0.1). Overall, cover crops may reduce sediment loss from agricultural landscapes, especially during high-risk periods, helping protect sensitive downstream waters.