Case Study: Nitrogen Cycling on Pasture-Based Dairy Farms

Most animal waste management plans for pasture-based dairy farms use estimates for the amount of manure produced and the yields of forage removed to design the waste plan. A trial was conducted to demonstrate how dairy producers could document agronomic nutrient application and removal on pasture-based dairy farms. This challenge was fairly complex because grazing animals are constantly harvesting forage and depositing manure. This work was conducted on a 160-head Holstein grazing dairy over 2 yr. The operator received a customized animal waste management plan, calibration of manure-handling equipment, and a detailed farm map. Standing forage was estimated daily, before and after grazing, by using a rising-plate meter, and measurements were recorded. Soil samples were taken at a depth of 30 cm at the end of each growing season (October 1) and tested for nitrates to determine N application residues. Estimated annual standing grass yields ranged from 8,736 to 21,056 kg DM/ha, with a mean of 16,912 kg. This DM was the equivalent of 225 to 659 kg N/ha removed. The dairy producer found this increased level of management rewarding because he had actual data to make decisions. Additionally, this increased management was more profitable. The second-year estimated grass yields increased 19.6% (3,182 kg/ha) in total DM produced over 1 yr. This project successfully demonstrated a new model of tracking N applications and removal in pasture-based dairy farms.