|Helmers, M -|
|Zhou, X -|
|Asbjornsen, H -|
|Kolka, R -|
|Cruse, R -|
Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 30, 2012
Publication Date: September 14, 2013
Citation: Helmers, M.J., Zhou, X., Asbjornsen, H., Kolka, R., Tomer, M.D., Cruse, R.M. 2013. Sediment removal by perennial filter strips in row-cropped ephemeral watersheds. Agriculture, Ecosystems and Environment. 41(5):1531-1539. Interpretive Summary: Conservation practices that can control soil erosion and sediment loss from agricultural fields need to be more widely implemented, especially under climatic conditions that include high intensity rainfall events. Many practices are tested in small plots without providing information about performance about sediment loss at the hillslope and small watershed scale. This study evaluated perennial filter strips and their capacity to reduce sediment losses from small hillslope-sized watersheds in a replicated experiment. The trial was monitored from 2007 through 2010, a period that included periods of near-record amounts of daily and monthly rainfall. Cropped areas were in a corn and soybean rotation and managed under no-tillage. Results showed the presence of filter strips reduced sediment loss by 96%, or from 3.6 to 0.2 tons of soil per acre (t/ac) on an annual average basis. Among watersheds where the filter strips were present, the proportion of the watershed in filter strip (10 vs 20%) and the distribution of the filter strips on the slopes (at the footslope or distributed in multiple contour strips) did not significantly influence sediment loss. On these 6-10% slopes, no-tillage alone did not prevent soil loss from approaching or even exceeding 'tolerable' losses of 5 t/ac under the patterns of high rainfall observed in 2008 and 2010, but the combination of no-tillage and filter strips was highly effective and always kept average soil loss to less than 0.5 t/ac. These results are of interest to agricultural producers who are concerned about erosion on sloping soils, and conservation planners and policy makers tasked with ensuring conservation practices are effective in reducing sediment losses and maintaining soil productivity under a changing climate.
Technical Abstract: Vegetative filter strips have been demonstrated as a practical strategy in reducing soil loss and nutrient transport from agricultural land. Their environmental benefits need to be further tested in long-term field experiments on a landscape scale. Twelve ephemeral (hillslope-scale) watersheds at the Neal Smith National Wildlife Refuge (NSNWR) in central Iowa were used to evaluate the effectiveness of prairie filter strips (PFS) in trapping sediment from agricultural runoff. Four treatments with PFS of different size and location (100% rowcrop, 10% PFS at footslope, 10% at footslope and in contour strips, 20% PFS at footslope and in contour strips) were seeded in fall 2006 using a balanced incomplete block design. All watersheds were under bromegrass (Bromus L.) cover for at least 10 years prior to the treatment. Cropped areas were managed under a no-till 2-yr corn (Zea mays L.)–soybean [Glycine max. (L.) Merr.] rotation beginning in 2007. Much (38-85%) of the total sediment export from cropland occurred in the spring or during the early growth stage of rowcrop due to wet field conditions and poor ground cover. The highest sediment concentration was observed in 2008 with wet weather and incomplete establishment of PFS vegetation. Thereafter, loads decreased and results showed the PFS were effective at trapping sediment during periods of severe erosion. The mean annual sediment yield through 2010 was 0.36 and 8.11 Mg ha-1 for the watersheds with and without PFS, respectively, a 96% sediment trapping efficiency for the 4-yr study period. While the PFS treatments reduced runoff amount by 34%, the decrease in sediment concentration in runoff was the primary factor that reduced sediment export. The amount and distribution of PFS had no significant impact on runoff and sediment yield, probably due to the relatively large width (27-41 m) of the PFS used in this study. Our findings suggest that incorporation of small amounts of PFS within annual rowcrop systems provide an effective approach to reducing sediment loss in runoff from agricultural landscapes.