Pasture Fertility

By Becky Mills
Progressive Farmer Contributing Editor

Like most cattle producers, Traci Talley has to cut corners at times. But don't ask her to shortchange her fescue, orchardgrass and clover pastures.

"When pasture fertility drops, the weeds and undesirable species start coming in," said the Halifax, Virginia, producer.

The best way to keep things in balance isn't new. It all comes down to fertility levels and pH. "You aren't going to eliminate weed pressure, but you can minimize it and allow forage plants to be more competitive," said Tennessee Forage Specialist Gary Bates. And that means better yields and improved production.

So how much is enough fertilizer? Stephen Barnhart, forage specialist in Iowa, said grass-based pastures usually respond well to the first 40 to 50 pounds per acre of nitrogen. Bluegrass continues to respond to nitrogen applications up to 150 to 180 pounds an acre, but at a decreasing rate. Tall cool-season grasses like bromegrass, orchardgrass and tall fescue respond to nitrogen levels up to 250 to 300 pounds, but like bluegrass, at a decreasing rate.

Legumes in the pasture complicate things a bit. Because the legumes fix nitrogen, you may need to adjust what you're adding. Too much nitrogen and the grass will crowd out the legumes. Barnhart's rule of thumb is if a pasture is made up of less than one-third legumes, treat it as a grass pasture. If it is more than one-third legumes, don't apply nitrogen.

BEYOND THE NITROGEN

With phosphorus and potassium, the response isn't nearly as dramatic or consistent as it is with a nitrogen application. Barnhart recommends adding enough of the two nutrients to keep pastures out of the low or very low levels, preferably getting them up to the optimum level. Grass responds to nitrogen more efficiently when phosphorus and potassium levels are adequate.

Don't forget about lime either, especially if you're trying to keep legumes productive. For grass-based pastures, aim for a pH of 6.0 to 6.5. For legumes, keep that pH a little higher—in the range of 6.5 to 7.0

While general guidelines are helpful, there is only one sure way to get the optimum amount of fertilizer and lime on pastures: soil-test. "Fertilizer and lime are too costly to overuse," said Virginia cattlewoman Talley. "On our pastures we soil-test every two years. On hay land where we're removing so much of the plant, we soil-test every year."

When testing, Talley aims for blocks of no more than 5 acres each in larger pastures, then takes around 25 samples per block. "Our soil types change so drastically in Halifax County," she said. "We go from clay to deep, sandy soil."

The more standard recommendation is to soil-test at least every three or four years. The first test gives you a short-term plan. If fertility levels are good, establish a maintenance plan. If levels are low, add fertilizer to build up the land. A follow-up test in three to four years will tell you if you've gotten on track.

Timing counts when it comes to pasture fertility too. Tennessee's Bates said cool-season grasses like fescue should be fertilized once in the spring then again in the fall for stockpiling. Apply phosphorus and potassium once a year, either in the spring or fall. When applying nitrogen in the spring, aim for a very early date (more like late winter) or a late one.

A late-winter application stimulates growth and makes grazing available earlier. Wait until later -- after the grass makes a seed head and you've grazed through it once -- to shift production into summer months when you can stockpile for grazing.

Talley said she opts for the early approach and puts litter from her broiler breeder houses out in mid-February before grass starts to green up.

Warm-season perennials like bahiagrass and bermudagrass call for split potash applications -- one at the start of the growing season and one halfway through.

Apply nitrogen at the start of the growing season. If you are cutting the grass for hay, apply more nitrogen after each cutting.

DURING A DROUGHT

Every year it's a gamble. Should you be an optimist and put down the recommended levels of nitrogen, potassium and phosphorus, even though we're in a drought?

Skip it if you don't have the moisture, said Tennessee forage specialist Gary Bates. "This is especially true with nitrogen. Otherwise you'll make the forage more toxic because plants will store nitrates rather than using them for growth."

When it does start to rain, though, have a supply of nitrogen on hand. Grasses can recover quickly after a drought. And if you applied potassium and phosphorus before you knew you would be in drought conditions, rest assured. It's probably still there and will give those forages a nudge when the rain finally does start.

(VM/CZ)

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