The same spring rains that lessen producers' concerns about drought can also lead to soil erosion and nutrient runoff. Keeping soil and fertilizers where they belong -- in the field -- benefits producers and the environment.
No-till farming, cover crops and rotational grazing will help producers reduce surface runoff to improve soil and water quality, according to South Dakota Agricultural Experiment Station researcher Sandeep Kumar, an assistant professor in the SDSU plant science department.
He and graduate student Sagar Gautam used computer modeling to determine which farm management methods will produce the best reduction in surface runoff through a $60,000 subcontract from a U.S. Department of Agriculture National Institute of Food and Agriculture grant.
Their work is part of a three-year, $482,000 research project led by Distinguished Professor Rattan Lal of the Ohio State School of Environment and Natural Resources. The goal is to determine which farm-management practices will improve soil and water quality on sloped land.
Adjusting model for South Dakota
Kumar and Gautam used the Agricultural Policy/Environmental eXtender (APEX) computational model developed using 40 years of data from the North Appalachian Experimental Watershed near Coshocton, Ohio.
The rolling Ohio landscape provides an ideal platform to study the long-term impact of crops and farm management techniques on the water quality of streams and rivers, according to Kumar, who contributed to the USDA proposal as a postdoctoral researcher at Ohio State.
In 1935, the USDA established the 1,050-acre watershed to determine which farming methods are appropriate for sloped lands. USDA Agricultural Research Service scientists have conducted soil water conservation studies on the watersheds since 1937.
Kumar and Gautam customized the model for South Dakota with soil conditions, management information and weather data from the last 10 years. South Dakota gets half the amount of precipitation that Ohio does, according to Kumar. However, he noted, "this model is universal -- it works everywhere."
Gautam said, "Once the model is ready, you can use different crops and then compare which one gives you more reduction in runoff." The researchers looked at small plots of approximately 2.5 acres, a nearly 20-acre field and even a large-scale model of approximately 27 sections of land to determine the impact of management practices up to 50 years from now.
Recommending management techniques
The computational model confirmed the value of using no-till in the Midwest to retain water and limit nutrient run-off, explained Kumar. "It improves water infiltration."
In a soybean-corn rotation, the use of cover crops, such as winter wheat or oats that can be harvested early, will reduce erosion, Kumar noted. "If there is more cover on the ground, this will minimize water losses."
The researchers also looked at management of orchard grass pastures on a 10 percent slope.
Rotational grazing is beneficial, Kumar explained, pointing out the soil must be properly managed. "When there is a lot of compaction, we are getting more runoff," Gautam noted.
Kumar recommended using perennial grasses, such as switch grass and big blue stem, to reduce runoff. In particular, strips of perennial grasses left ungrazed on the borders between pastureland and waterways provide a buffer to help control runoff and subsequently improve the water quality of streams and rivers.
These findings agree with other studies, Kumar pointed out. However, the next step will be to determine the size and number of strips that are needed based on the slope and size of the grazing lands.
Considering climate change, Kumar and Gautam found that increased precipitation has a direct influence on runoff at a field scale, while increasing or decreasing temperatures have no significant impact.
When considering climate change impacts on a larger watershed scale, Kumar said, "It will take longer to get a better answer, and research is still on-going."
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