ASABE Technical Library - Abstract

The Effect of Cover Crops on Water Quality at a Watershed Scale

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Soil Erosion Research Under a Changing Climate, January 8-13, 2023, Aguadilla, Puerto Rico, USA  .(doi:10.13031/soil.23090)
Authors:   Shalamar D Armstrong, Michael D Ruffatti
Keywords:   Cover crops, Nitrogen, Nonpoint source pollution, Phosphorus, Tile drainage, Water quality, Watershed.

Abstract

In the United States, the contribution of nitrogen (N) from the Upper Mississippi River Basin (UMRB) to the hypoxic zone of the Gulf of Mexico continues to be an environmental and sustainability issue for row crop agriculture. The majority of Nutrient Loss Reduction Strategies (OH, MN, IA, and IL) identify cover cropping as the most effective in-field conservation strategy that can be adopted on a large scale to achieve the non-point nutrient loss reduction goals. Several plot scale studies across the UMRB have demonstrated that cover crops have the capacity to reduce N losses via tile drainage by 30-50%. These results were demonstrated on less than 5 acres, where scientist have total experimental control of key variables such as nitrogen management, crop rotation, tillage, crop variety and maturity and percentage of cover crop adoption. However, cover crops have not been tested thoroughly on a watershed scale, where scientist have no control of the aforementioned variables and where 100% cover crop adoption is highly unlikely.

In order to meet the nutrient loss reduction goals that are proposed in the Illinois Nutrient Loss Reduction Strategy, mass scale cover crop adoption on a watershed scale must be employed. Thus, there is a need to test the commonly selected cover crops in our region on a watershed scale, where there is little to no scientific control and partial adoption to determine if partial adoption of cover crops can impact water quality as it refers to N losses via tile-drainage and phosphorus (P) losses through surface runoff events. Therefore, our objectives were to determine the impact of mass adoption of cover crops on nitrogen tile drainage water and surface runoff P loss.

In the Lake Bloomington Watershed of Towanda, IL, we identified two sub-watersheds that drain into Money Creek, the mainstem stream that flows into Lake Bloomington (Figure 1). The treatment watershed is 465 ha (1100 acres) and receives cover crop application on approximately 50% of the drainage area and is drained by a 24-inch tile main. The reference watershed (Control) is 262 ha (770 acres) and is not treated with cover crops. The reference watershed is drained by two 12-inch tiles and one 8-inch tile (more details of dominant land use and soil type, crop rotation, and N management in Figure 1 for treatment and reference watersheds). After a successful aerial seeding of cover crops since the fall of 2017 on 49% of the treatment watershed, we observed a reduction in tile-drainage water NO₃-N concentration for the cover crop watershed relative to the reference (control) watershed that was consistent throughout the study (Figure 2). Furthermore, when considering NO₃-N loads (mass of NO₃-N per 1000 gallons per day), cover crop adoption resulted in a 38% reduction relative to the reference watershed for the entire study period. These observations demonstrate the ability of cover crops to interact and scavenge soil nitrate from the residual and legacy N pools that would otherwise be susceptible to loss via tile-drainage.

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