Joel P. Tilley

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 (CuSO4) 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.

Atmospheric Deposition Effects on Surface Waters, Soils, and Forest Productivity

When acid rain was discovered to be a regional problem in North America in the 1970s, initial concerns focused on surface-water acidification. Some of the earliest acidic deposition research found that fish populations in some lakes and streams in the Adirondack Mountains of NY had been eliminated by acidification (Schofield, 1976). In the 1980s, research in the U.S. expanded greatly through the National Acid Precipitation Assessment Program (NAPAP) to include soils and forests, as well as aquatic ecosystems. Because little environmental monitoring had been done before the start of NAPAP, however, information on changes that led to the conditions observed in the 1970s and 1980s was limited. As a result, NAPAP research focused on assessments of current conditions, short-term experimental manipulations, reconstructions from paleolimnological evidence, and mathematical modeling, to investigate past and possible future changes caused by acidic deposition. This program yielded conclusive evidence that acidic deposition had acidified poorly buffered surface waters, resulting in the loss of fish populations and other aquatic organisms, although uncertainties remained about the extent of these effects (NAPAP, 1991). The NAPAP Integrated Assessment Report (NAPAP, 1991) also concluded that acidic deposition may have affected soil chemistry but effects on forest health were not apparent, except for high-elevation spruce-fir forests where stand dieback was attributed to acidic deposition.