|Powell, J Mark|
Submitted to: Wisconsin Fertilizer Aglime and Pest Management Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/18/2001
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: In general, many dairy farmers continue to consider manure as a waste, something that needs to be disposed of with least economic cost. Only in the last 10 to 15 years has there been a concerted effort to reintroduce manure as a valuable source of plant nutrients. However, even though proper manure management can be profitable because of reduced fertilizer costs, many farmers do not credit the nutrients contained in manure. The lack of manure nutrient crediting by farmers may be due to many factors that make dairy manure an undependable source of plant nutrients. One of these factors includes the inherent shortcomings of the classical, indirect methods used to estimate manure nutrient availability to crops. This paper reports preliminary results of a long-term study that used the stable isotope 15N to compare direct and indirect determinations of N flow in various components of the feed-animal-manure-soil/crop continuum of dairy systems. We expect the results of this project to have several theoretical, as well as practical, implications for improving environmental impacts of dairy manure management. The 15N technique should provide a tool for better understanding N flow in various components of the animal-feed-manure-soil/crop-environment continuum. 15N-labeling of dairy manure using the inorganic method may provide a less expensive and less difficult tool for making direct measurements of short-term (e.g single cropping season) manure N transformations. The field trial is designed to evaluate the effects on N cycling of various manure management strategies, including the current, predominant practice of Wisconsin farmers: the repeated application of large manure amounts to the same field. The long-term nature of the trial (6-yr minimum) and the use of 15N-labeled manure and fertilizer N should provide opportunities for comparing direct and indirect measurements of manure nutrient dynamics under various manure management regimes. It is expected that this information will increase our confidence in manure N credits. Ultimately, these studies may provide the basis for developing alternative, economically viable and environmentally sound manure management practices.