Improving dairy farm sustainability II: Environmental losses and nutrient flows

This paper continues the analysis of nutrient management on a case study dairy farm in New York State. In Part I, it was found that 60 to 70% of the imported N and P were not accounted for in the exported milk, crops, and animals. The purpose of this paper is to present a process for accounting for the fate of the excess nutrients and to determine the extent to which they were contributing to air and water pollution from the farm. Environmental losses of N and net excess of P in different subsections of the farm were estimated. Losses of N from volatilization on the barn floor and in storage were estimated to be 16% of excreted N, As a partial check on these results, manure nutrient composition for lactating cows was analyzed at excretion, entering storage, and leaving storage. Soil leaching losses from the farm were calculated using the LEACHN model, and were 9% of total N inflows to the farm. Predicted nitrate N concentrations in the leachate were 10.6 ppm. Results from monitoring a stream originating from the farm gave an annual average of 14.4 ppm of nitrate N, About 80% of the total N inflows were accounted for as milk sold (25%), animals sold (2%), leaching losses (9%), and volatilization/denitrification losses (46%), Environmental losses accounted for 75% of the excess N, Projected scenarios for increased use of farm-produced forages, reduction in fertilizers, and increased feed conversion to milk resulted in only minor improvements in the nutrient imbalance on this farm.