Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2006
Publication Date: N/A
Citation: N/A Interpretive Summary: Dairy farmers often apply manure to the same fields, year-after-year. Crop nutrient management plans require information on nutrient availability from previous manure applications. A six-year field trial was conducted in central Wisconsin. Semi-solid dairy manure was applied at two rates, either every year, every two years, or every three years to estimate first-, second-, and third-year dairy manure N availability. Estimates of second- and third-year manure N availability averaged 10 and 2% of total manure N applications using the "classical" indirect methods, and were highly variable. Estimates of second- and third-year manure N availability using 15N-labeled manure (direct method) were much less variable and averaged 6% and 2% in the second- and third-year, respectively. University of Wisconsin Cooperative Extension has used this information to revise recommendations on residual manure N availability to corn.
Technical Abstract: It is common practice to repeatedly apply dairy manure to the same fields. To accurately assess the total plant availability of manure nutrients, it is necessary to account for the nutrients remaining in soil from previous manure applications. A field experiment studying manure nitrogen (N) uptake by corn (Zea mays L.) was conducted from 1998-2003 on a Plano silt loam (fine-silty, mixed, mesic, Typic Argiudolls). Plots received two rates of manure: either every year, every two years, or every three years in order to estimate first-, second-, and third-year dairy manure N residuals. Residual manure N availability was estimated from single and multiple manure applications using 1) the fertilizer N equivalence method, 2) the apparent recovery (difference) method, 3) relative effectiveness method, and 4) recovery of 15N labeled manure. Second-year availability after a single manure application using the fertilizer equivalence and difference method was estimated to be 11.6 and 8.4% of total manure N applications, respectively. Estimates of third-year availability by these indirect methods were 2.8 and 1.4%, respectively. Measurement of 15N recovered from labeled manure was 5.6 and 2.0% in the second- and third-year, respectively. Fertilizer equivalence and difference methods showed great variability, making it difficult to estimate residual manure N availability, but using 15N labeled manures reduced variability.