Assessing the effect of management intensive grazing on water quality in the northeast US

Stocking rate is the key determining effect of management intensive grazing on dairy farm profitability. However, increased stocking rate can increase NO3- leaching from pastures. Increasing stocking rate increases NO3- loss through leaching because the bulk of the N consumed by the animal is excreted in concentrated areas of the pasture mainly in urine. We used experimental data from the northeast U.S. and the literature to assess the relationships between stocking rate and NO3- leaching losses beneath an intensively grazed pasture. A relatively low cumulative seasonal stocking rate of about 200 mature Holstein ha(-1) could result in a 10 mg l(-1) NO3-N concentration in the leachate beneath a fertilized, intensively grazed pasture. This means that while management intensive grazing can improve farm profitability and help control erosion, it can have a significant negative effect on water quality beneath pastures. The extent to which this effect occurs within specific watersheds needs to be evaluated in context of the other cropping systems and land uses within the watershed.