Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2006
Publication Date: 10/15/2006
Citation: Cusick, P.R., Kelling, K.A., Powell, J.M., Munoz, G.R. 2006. Estimates of residual dairy manure n availability using various techniques. Journal of Environmental Quality. 35:2170-2177. Interpretive Summary: Dairy farmers often apply manure year after year to the same fields. When calculating crop nutrient requirements, information is needed on nutrients available not only from present, but also from previous manure applications. A six-year field experiment 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 nitrogen availability. Estimates of second-year availability after a single manure application using common indirect methods were 11.6 and 8.4% of total manure nitrogen applications, respectively. Estimates of third-year availability by these common methods were 2.8 and 1.4%, respectively. Direct measurements using manure labeled with the stable isotope 15-nitrogen were 5.6 and 2.0% in the second- and third-year, respectively. The indirect methods showed great variability, making it difficult to estimate residual manure N availability. Using 15-nitrogen manure reduced variability considerably. This information will assist extension agents and farmers in better prediction of manure nitrogen availability to crops, therby reducing risks of manure application in excess of crop nitrogen requiremnets, nitrogen loss, and environmental contamination.
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.