Figure costs carefully before deciding on nitrogen rates for cool-season pastures
Much of the nitrogen applied to tall fescue and smooth bromegrass hay meadows and pastures goes on in January or February in eastern Kansas.
The amount and timing of nitrogen depends on whether the field is hayed or grazed; how much, if any nitrogen was applied in the fall; the price of nitrogen and hay; and the growing conditions since last fall, said Kansas State University agronomist Dave Mengel.
For fields that will be hayed, normal nitrogen fertilization rates for established fescue and bromegrass hay fields are 90 to 120 pounds of actual nitrogen per acre, or about 30 pounds of nitrogen per ton of expected yield, said Mengel, who is a soil fertility specialist with K-State Research and Extension.
A recent summary of fescue and bromegrass nitrogen response data shows that across nearly 100 experiments in Kansas, the average yields for unfertilized plots was 1.35 tons of hay per acre, while maximum yields averaged 3.15 tons of hay with 140 pounds of nitrogen, he said.
"Doing some simple cost-and-return calculations, using a long-term average value of $60 per ton as the value of the hay produced and 50 cents per pound of nitrogen, the normal rates of nitrogen (90 to 120 pounds per acre) are appropriate to maximize profit in most years. It will be important to watch nitrogen costs, however, as they continue to be volatile," Mengel said.
The other issue is hay price and supply, he added. With the drought, prices for grass hay have been considerably above the long-term average of $60 per ton. If hay prices remain high in 2013 and nitrogen prices for urea continue in the range of 50 cents per pound, applying nitrogen rates at the upper end of the 90- to 120-pound range should be most profitable.
"But going beyond that 120-pound nitrogen rate would still not be cost effective," he added.
One issue these calculations don't consider is hay quality, Mengel said.
"Protein levels will be increased at the higher nitrogen fertilizer rates. So in cases where producers are relying on high-quality hay as their primary protein source, they may want to push nitrogen rates a little higher, or add supplemental protein to rations at the lower nitrogen rates," he said.
Tall fescue and smooth bromegrass pastures that will be grazed in both spring and fall should receive about 100 pounds total nitrogen per acre, with 60 percent applied in the winter or early spring, Mengel said. Producers should plan on applying 60 to 70 pounds nitrogen per acre in winter or early spring, starting as early as January or February.
In any type of fertilizer management program for tall fescue and smooth bromegrass, for best results, needed phosphorus and potash should be applied in the late summer, along with a light application of nitrogen, he said. Rates should be based on soil tests.
"Phosphorus will help the grass develop a good root system for the winter, and develop buds for new tillers the next spring. Phosphorus and potassium applied in winter or early spring won't provide the same benefits," the agronomist said.
One additional nutrient that producers should consider watching for tall fescue and smooth bromegrass pastures or hayfields is sulfur.
"If the pasture or hayfield is receiving adequate nutrients and precipitation, but is dropping off in production, it could be deficient in sulfur. Sulfur deficiency will cause a general reduction in forage production long before it results in visual deficiency symptoms," Mengel said. "An application of sulfur to a tall fescue or smooth bromegrass pasture or hayfield that is deficient in sulfur can result in forage yield increases of as much as 500 to 800 pounds per acre."
To determine whether phosphorus, potassium, sulfur, or lime are needed on tall fescue and smooth bromegrass fields, producers should consider soil sampling, he added. The best time to sample is 30 days prior to fertilizer application.
Samples for a phosphorus and potassium soil test should be taken to a 6-inch depth. A profile test to a depth of 24 inches should be used to evaluate sulfur needs, he said.