POTENTIAL AND LIMITATIONS OF COVER CROPS, LIVING MULCHES, AND PERENNIALS TO REDUCE NUTRIENT LOSSES TO WATER SOURCES FROM AGRICULTURAL FIELDS IN THE UPPER MISSISSIPPI BASIN

Authors: Kaspar, Thomas; KLADIVKO, E - PURDUE UNIVERSITY; Singer, Jeremy; MORSE, S - UNIVERSITY OF MINNESOTA; MUTCH, D - MICHIGAN STATE UNIVERSITY

Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 10/23/2007
Publication Date: 3/15/2008
Citation: Kaspar, T.C., Kladivko, E.J., Singer, J.W., Morse, S., Mutch, D. 2008. Potential and limitations of cover crops, living mulches, and perennials to reduce nutrient losses to water sources from agricultural fields in the upper Mississippi basin. In: Final Report: Gulf Hypoxia and Local Water Quality Concerns Workshop. St. Joseph, Michigan, ASABE. p.129-148.

Interpretive Summary: Losses of nitrate and phosphorus from corn and soybean fields in the Upper Mississippi River basin contribute to contamination of the Mississippi River and the Gulf of Mexico. Even when farmers carefully manage fertilizers and put on only what is needed by the crop, substantial nutrient losses occur during the fall, winter, and spring when corn and soybean are not growing and the fields are bare. One way to prevent these losses is to grow plants to take up nutrients and protect the soil surface when the main crops are not present. Cover crops, living mulches, and perennial crops can fill the gap between harvest and planting of corn and soybean. Cover crops are plants that grow only during the period between harvest and planting of the main crops. Living mulches, grow year round between the rows of the main crop, but are suppressed with mowing or herbicides during the summer. Alternately, perennial crops, like alfalfa, would replace the corn and soybean crops altogether. All three of these approaches have advantages, disadvantages, and potential applications. It is generally accepted by scientists that these practices have the potential to reduce nutrient losses, but their adoption is limited by management problems, unfamiliarity of farmers with these practices, and lack of financial incentives. Continued research is needed, but these practices in conjunction with fertilizer management and other practices can reduce nutrient contamination of the Mississippi River and other surface waters, which will benefit farmers and the general public.

Technical Abstract: Losses of nitrate and phosphorus to water resources in the Upper Mississippi River basin threaten aquatic ecosystems and impair water sources. Numerous studies at the field and watershed scale have shown that a significant proportion of the nitrate and phosphorus in surface waters comes from agricultural land used for corn and soybean grain production. Attempts to reduce nitrate and phosphorus losses to surface waters in this region have focused on fertilizer and manure management. Unfortunately, previous research has shown that even when fertilizers are applied at less than the economic optimum rates, significant losses of nutrients still occurs. This happens in part because there are extended periods during each year when living plants are not removing nutrients from the soil and the nutrients are susceptible to losses. Summer annual grain crops, like corn and soybean, accumulate water and nutrients only for about four months of the year. Cover crops, living mulches, and perennial crops, however, can extend the period of active nutrient and water uptake in agricultural systems. Lengthening the period of active uptake, increases annual plant uptake of nutrients, reduces soil concentrations of nutrients, and provides living plant cover for the soil surface, thus reducing the potential for nutrient and sediment losses into surface waters. This literature review discusses the potential, benefits, and disadvantages of cover crops, living mulches, and perennial crops in the Upper Mississippi River basin. All three practices have the potential to reduce nutrients losses from agricultural lands in specific applications, but their adoption is limited by lack of knowledge about these practices, unmet research needs, and financial incentives for farmers.