Journal of the NACAA
ISSN 2158-9429
Volume 1, Issue 1 - July, 2008


Developing a System to Track Nitrogen Cycling on Pasture-based Dairies

Downing, T.W., Tillamook County Extension, Oregon State University


Most animal waste management plans written for pastured based dairies use estimates for manure produced and yields removed to design the waste plan. Landowners theoretically have been required to apply nitrogen (N) in quantities equal to what they remove annually in a crop. As concerns for water quality have increased, so has the need to demonstrate that the nutrients applied are equal to what is removed. The objectives of this research were to develop a system to document nutrient application and removal on pasture based dairies. This challenge was fairly complex, because grazing animals are constantly harvesting forage and depositing manure. Additionally, grass growth over time is a factor. This work was conducted on a 200 head Holstein grazing dairy over two years. An animal waste management plan was written, manure handling equipment calibrated, and a detailed farm map developed. Daily forage measurements were recorded before and after grazing. Soils samples were taken at 12" deep at the end of each growing season and tested for nitrates to determine nitrogen application residues. Annual grass yields ranged from 3.9 to 9.2 tons of dry matter/acre with an average of 7.55 tons. Pasture protein levels varied some throughout the season, but were averaged to determine the approximate level on nitrogen removed. Total nitrogen removed per acre by grazing ranged from 201 up to 526 lbs. of N/acre removed. The cooperator found this increased level of management rewarding and profitable. Having good data gave him the confidence to add commercial fertilizer and recorded a 20.1% (1.45 tons/acre) increase in total dry matter produced in year two over year one. This project successfully demonstrated a new model of tracking nitrogen applications and removal in pasture-based dairies and has been adopted by others in our region.
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