Nutrient management in pastures presents special challenges, mainly because cattle tend to congregate in certain areas, leaving more nutrient deposits of manure and urine around shade or water tanks.
This usually results in too many nutrients in some areas and not enough in others.
Kevin Shelley, with the University of Wisconsin-Extension Nutrient Pest Management Program points out, "Manure and urine are important sources of nutrients for pasture forage production. The challenge in grazing systems is to assure optimal distribution of manure nutrients across and throughout the pastures."
Shelley recommends maintaining heavy grazing pressure in small areas for short periods of time, then rotating livestock to the next paddock. This reduces the potential for livestock to graze selectively, feeding more in some areas than in others.
While many producers, particularly dairy producers, tend to follow this practice, he said there are further steps graziers can take to insure more even distribution of nutrients.
"Provide water sources throughout the pasture so that livestock do not need to leave the rotated grazing areas to drink," he suggests. "Cattle oilers, scratchers and supplemental feed bunks are best moved out to grazing areas as well for nutrient distribution purposes."
He further recommends limiting access to areas where livestock routinely congregate and lay when not grazing, such as shade or shelter, when these areas are not essential.
When it is hot, he suggests providing shade on one side of the paddock and water on the opposite side to encourage the animals to walk from one area to the next and not congregate in one place.
When doing a nutrient management plan for pastures, start with soil tests of the pastures. Then consider what pasture crops are growing there, including the ratio of legume to grass.
"When a pasture sward contains a significant percentage of legumes, such as alfalfa or clovers, nitrogen additions are not recommended," he illustrates. "The legume species biologically fix nitrogen for their own use, and provide some nitrogen to companion grasses as legume plant roots, crowns and leaves decompose and regenerate."
He adds, "If you really want to optimize productivity in the short run, fertilize with nitrogen but not over the long-term and if you do fertilize, split applications are better."
He points to research done at the University of Wisconsin-River Falls by Dennis Cosgrove indicating that the ideal times for nitrogen application are May 1 and August 1.
In mid-June and early-July, the heat of the summer and the warm nights shut down the metabolism of the grass and the plants will not respond to the addition of nitrogen.
When pastures are properly managed with good manure distribution, there is usually efficient cycling of phosphorus and potassium between grazing livestock and forage production.
The need for these nutrients may be minimal, he suggests, particularly when grazing livestock are supplemented with other feeds.
He says the need for potassium and phosphorus additions is best determined by updated soil testing every three or four years. When soil tests indicate a need for fertilizer, take credits for the manure that is provided by the livestock.