The influence of prairie strips sown in midwestern corn and soybean fields on sediment discharge throughout the year

Abstract

Many crop fields in the United States Corn Belt continue to erode at rates in excess of soil regeneration leading to sediment being transported from farms to adjacent surface water and degrading wildlife habitat. To reduce or eliminate sediment loss, vegetative filter strips can be established perpendicular to the hillslope and at the edge-of-field to intercept and filter surface runoff transporting sediment. The filter strips can be planted with native prairie vegetation to filter sediment out of runoff as well as establishing high quality habitat. A long-term study at Neal Smith Wildlife Refuge Farm in central Iowa found that with as little as 10% of a field converted to prairie filter strips, sediment discharge from fields could be reduced up to 95%. To improve our understanding of prairie filter strips and erosion processes over a broader range of landscapes, this study was conducted at six farm sites throughout Iowa. Following a paired treatment approach, each farm site was broken into two different subcatchments; one subcatchment was fully cropped (control) while the other had a portion of the field sown with native prairie vegetation. Each subcatchment had an H-flume installed to sample runoff water and determine the total suspended sediment (TSS) load and a rain gauge to monitor rainfall amount, frequency, and duration. Between 2016 and 2021, subcatchments with prairie strips median TSS load was 89.5% lower (95% CI, 69.2% to 96.4%, p < 0.001) than the control subcatchments. In fields when corn was planted, the subcatchments with prairie strips had significantly lower TSS discharged, with a median TSS load 97.6% less (95% CI, 92.1% to 99.3%, p < 0.001) compared to the control subcatchments. The TSS loads were significantly influenced by the amount of rainfall (p < 0.001) despite the treatment. To investigate effects of seasonality and rainfall amount, the data set was parsed out based on the growing season of the dominant cropping system. There was no prairie strip effect during the primary growing months (PGS) (May to August); however, outside of the primary growing months (OPGS) (March to April and September to November) the prairie strip subcatchments median TSS load was 96.1% less (95% CI, 82.5% to 99.1%, p < 0.001) than the controls. The significant interaction of crop planted with prairie strip treatment and the differences between PGS and OPGS suggest that prairie strips have the capacity to reduce sediment leaving a field when they are the most vulnerable to effects of splash erosion (i.e., low ground cover and higher rainfall amount). Climate change models predict that areas like Iowa will continue to trend toward higher frequency and intensity rain events, so the compounded benefits of prairie planted in cropped fields could promote biodiverse landscapes that increase resilience to predicted effects from climate change during parts of the year when the land is more susceptible to erosion.