|Zhou, Xiaobo -|
|Helmers, Matthew -|
|Asbjornsen, Heidei -|
|Kolka, Randall -|
|Cruse, Richard -|
Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 31, 2013
Publication Date: N/A
Interpretive Summary: Losses of nitrogen and phosphorus from agricultural fields can impact aquatic ecosystems and the beneficial use of water resources. Each agricultural producer needs information to understand which conservation practices can most effectively limit these nutrient losses from his/her farm. This study evaluated prairie filter strips as one practice that can decrease nutrient losses in runoff from rolling cropland in Iowa. Prairie filter strips were seeded with an array of native species, and arranged on field-sized watersheds to cover 10 or 20% of the area, and at either the footslope or in narrow contoured strips. A corn–soybean rotation was grown on the cropped land, using no-tillage management. A suite of water quality and biodiversity responses to prairie strips are integrated into this research. During five years (2007-2011), nutrient losses were dominated by a few extreme rainfall runoff events, and the prairie filter strips effectively decreased those losses, with load reductions of 84% for total nitrogen and 90% for total phosphorus. The amount and placement of the filter strips did not significantly affect this result. Prairie filter strips can be placed at footslope positions to be most compatible with field operations, and be highly effective in reducing losses of nutrients from moderately sloping (6-10%), no-tilled cropland, during large runoff events. These results are of interest to the agricultural and conservation communities who need to understand how conservation practices can effectively protect water resources, even during extreme events.
Technical Abstract: Nitrogen and phosphorus from agricultural landscapes have been identified as a primary source of excess nutrients in aquatic systems. The primary objective of this study was to evaluate the effectiveness of prairie filter strips (PFS) in removing nutrients from cropland runoff in 12 small watersheds in Central Iowa. Four treatments with PFS of different spatial coverage and distribution (100% row-crop, 10% PFS of total watershed area at footslope, 10% PFS at footslope and in contour strips, 20% PFS at footslope and in contour strips) were arranged in a balanced incomplete block design across four blocks in 2007. A no-till two-year corn (Zea mays L.) –soybean [Glycine max. (L.) Merr.] rotation was grown in row-cropped areas beginning in 2007. Runoff was monitored by H flumes and runoff water samples were collected during the growing seasons to determine concentrations of nitrate-nitrogen (NO3-N), total nitrogen (TN) and total phosphorus (TP) through 2011. A few large events dominated the nutrient losses and the PFS treatments were effective in decreasing those losses. Overall, the presence of PFS reduced NO3-N, TN, and TP concentrations by 35, 73, and 82%, respectively, and reduced NO3-N, TN, and TP loads by 67, 84, and 90%, respectively. However, the amount and distribution of PFS had no significant impact on runoff and nutrient yields. The findings suggest that incorporation of PFS at the footslope position of annual rowcrop systems provides an effective approach to reducing nutrient loss in runoff from small agricultural watersheds.