The optimum time to apply N is early May and early August.
Split nitrogen (N) applications have long been recommended on rotationally grazed pastures. However, the most efficient timing for these nitrogen applications to rotationally grazed pastures has not been established.
Research conducted by Wisconsin Extension faculty determined that the optimum time to apply nitrogen is early May and early August. Mid-June applications are not productive because cool season grass (i.e. timothy, orchardgrass, and bromegrass) growth is slowed by summer heat and reduced precipitation.
Split applications of nitrogen or a single, well-timed application resulted in the highest yield. Three applications of 50 units of nitrogen each, and a single application on May 1 provided the highest overall yield. Single applications of 50 units of nitrogen on either May 1 or August 1 provided the greatest forage increases per pound of nitrogen applied. The single 50 unit application on June 15 consistently provided the lowest yield increase and the lowest yield increase per pound of nitrogen applied.
The greatest return per dollar were realized with the May 1 application and the three 50 unit applications. The lowest return was from the June 15 single application. It is important to realize, in early May, that pasture growth may already be greater than the animals' ability to utilize it. Nitrogen applications at this time will only exacerbate this problem.
In order to capture this increased growth, pastures may need to be mechanically harvested, have a reduced resting period, or stocked with higher than normal stocking rates.