However, several general findings may still be derived, as discussed below. Several are interdependent, often resulting in difficulty isolating the relative effects of any particular parameter compared to another and, in some cases, contradictory research results are found. Included, but not limited to, are slope, soil type, depth of freeze, rate of thaw, depth of snow, presence of cover crops, tilling practices, manure moisture content, and timing of application. There are several parameters that ultimately determine the impact winter manure spreading will have on the environment and the nutrient content that remains in the soil after application. Additionally, the loss of nutrients during spring thaws means a loss of soil productivity for farmers and added expense to purchase soil amendments. The emergence of environmental issues downstream of livestock operations such as algae blooms and fish kills has led some States to ban winter manure application all together, although some states still allow emergency applications and exempt smaller farms from the regulations. The US Environmental Protection Agency (EPA) and the Natural Resource Conservation Service (NRCS) discourages the application of manure in winter because of the elevated risk of nutrient loss to the environment as demonstrated by several field, laboratory, and modeling studies (Srinivasan et al., 2006). Contaminants of concern, emerging pollutants, case studies, existing best management practices, state level policy, and key data gaps were identified. What did we do?Ī comprehensive literature review was conducted that included scientific, technology transfer, and regulatory documents.
Based on this literature review, research needs and future directions were identified. Interest in winter manure application has increased, in part, due to the high-profile nutrient impacts to the Great Lakes and the several resulting new policies that have been implemented within the surrounding states. To better understand the state of the science and to lessen the present risk of winter manure application, a literature review was conducted that examined a wealth of studies dating back to 1945.
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