Manure management and nutrient loss under winter conditions: A literature review

ABSTRACT:

Excessive losses of nitrogen (N) and phosphorus (P) from agricultural fields have detrimental impacts on environmental quality. Nutrient management guidelines, such as the P Index, are designed to minimize the risk of nutrient loss with minimal disruption to the whole farm operation. Restricting winter spreading of manure, which is common to most management guidelines developed for cold climates, is a contentious issue in the northern-tier states of the United States and almost all provinces of Canada. Producers have strong opinions with regard to the merits of winter spreading and arguments against the alternative practice of manure storage. The purpose of this paper is to review the results of scientific studies relevant to the issue of winter spreading of manure, and identify needs for additional research in this area. Collectively, these studies illustrate the complexity of N and P dynamics in response to a wide spectrum of winter conditions. They do shed some light on the potential for nutrient loss following manure application during winter with respect to cropping system effects on runoff, manure mulching effects, manure properties, and differences due to manure placement relative to a snow pack and timing of application. However, process-level understanding of nutrient loss following manure application during winter is still lacking, and critical variables that control hydrologic and transport processes under winter conditions are not fully identified or understood. Extensive watershed-scale observations in combination with plot and field scale experiments that focus on specific processes should yield sufficient knowledge and data to develop empirical models, a useful first step in developing more detailed understanding of nutrient losses associated with manure spreading under winter conditions.