Validation of feed and manure data collected on Wisconsin dairy farms.

An on-farm study of 54 representative Wisconsin dairy farms was conducted to evaluate the influence of biophysical and socioeconomic factors on overall feed, fertilizer, and manure nutrient use. This report validates 1) how well data on cow diets, feed analyses, and milk production reflected established feed-milk-manure relationships; and 2) how well farmer-recorded data on manure land application reflected literature values of manure N and P excretion, collection, and loss. Calculated feed N and P use efficiencies (18 to 33% and 18 to 35%, respectively) fell within ranges expected for dairy farms. This suggested that our on-farm methods of data collection provided reliable information on relationships among feed N and P intake, secretions in milk, and excretion in manure. On stanchion farms, there were no differences between farmer estimates (kg/farm) of manure P collected (1,140) and land-applied (1,210) and what would be calculated from the literature (1,340). On freestall farms, there were no differences in amounts (kg/farm) of manure P collected (2,889), land-applied (2,350), or literature estimates (2,675). Manure P applications (kg/ha) to tilled cropland would be similar using either farmer estimates of manure collected and land-applied, or literature estimates. The data provided a snapshot of Wisconsin industry practices, as well as information on the range of feed and manure management practices on individual dairy farms. Improvements to data collection methods would require increased skill and training of both farmers and those responsible for assisting farmers in on-farm data collection and analyses.