Manure Nutrient Content on Vermont Dairy Farms: Long-Term Trends and Relationships

Manure nutrient analysis is an important component of nutrient-management planning on dairy farms. The University of Vermont Agricultural and Environmental Testing Laboratory analyzed more than 2,300 dairy manure samples from 1992 to 2006. Means of nutrient content were consistent with published values, but variability among the sample results supports the need for laboratory analysis to determine manure application rates. Phosphorus (P) content of manure decreased by about 30% from 1992 to 2004, presumably reflecting a shift in dairy diets to avoid feeding excess P, but P content increased in the following 2 years. The copper (Cu) content of liquid manure increased four-fold, mostly after 1998, a change attributed to increased use of copper sulfate (CuSO(4)) in foot baths. While not reliable for making nutrient-management decisions on individual farms, long-term summaries can be useful to detect trends and to put individual analytical results in context.