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Forage crops: soil testing to manage nutrient costs

With fertilizer prices at a near record high, the admonition to base fertilization on soil tests should not have trouble being heard. Soil testing remains one of the cheapest practices a forage producer can use. For the past few years, fertilizer prices have increased significantly and have not come down much — producers must learn to manage costs and maintain optimum production. Fertility recommendations should be based on how much nitrogen, phosphorus and potassium, as well as secondary and micronutrients are available in the soil.

It’s a sermon the Extension Service has preached for years, but with fertilizer prices at a near record high, the admonition to base fertilization on soil tests should bring new converts into the fold.

“Soil testing is one of the cheapest practices a forage producer can use,” said Texas AgriLife Extension forage specialist Vanessa Corriher, speaking at the annual Ag Technology Conference on the Texas A&M-Commerce campus.

“For the past few years, fertilizer prices have increased significantly and have not come down much,” Corriher said.”So producers must learn to manage cost and maintain optimum production.”

Fertility recommendations should be based on how much nitrogen, phosphorus and potassium, as well as secondary and micronutrients are available in the soil. “If you don’t know what nutrients you need and at what rate, you either waste money or lose production.”

A $12 bargain

Producers should set production goals for hay production or grazing and fertilize accordingly. “Without soil test recommendations, it’s just a guessing game. At $12 per sample, soil testing is a bargain.”

She recommends annual testing for hay production. “Taking hay off removes nutrients and changes the soil environment every time you cut and bale.”

For pastures, she said testing every two or three years should be adequate and that recommendations will consider credits for nutrients already available. “Cattle recycle nutrients with feces and urine in pastures. Nutrient recycling is less in hay meadows.”

Producers should take a standard sample, from 0 to 6 inches deep, for nitrogen, phosphorus and potassium. They might also want a deeper sample to detect nutrients at 12, 18 or 24 inches. She said secondary nutrients—calcium, magnesium and sulfur—are also important, along with micronutrients—copper, iron, manganese and zinc.

N, P and K

“Nitrogen, phosphorus and potassium are needed in the largest quantities.”

Corriher said producers should set production goals and fertilize to meet those standards. For a 1 ton per acre forage production goal, coastal bermudagrass needs 50 pounds of nitrogen, 14 pounds of phosphorus and 42 pounds of potassium. For 2 tons, rates increase to 100, 28 and 84.

One ton production would need 8 pounds of calcium, 3 pounds of magnesium and 4 pounds of sulfur. The rate increases to 15, 6 and 8 for a 2 ton yield goal.

Nitrogen may be the most essential nutrient. “Without nitrogen we get no growth. If nitrogen is deficient, grass will have a yellowish color,” she said. Ample nitrogen improves the grass’ ability to compete with weeds “and possibly decrease herbicide needs. Also, nitrogen increases forage production and crude protein.”

Nitrogen is mobile, leaches and volatizes.

Phosphorus, Corriher said, stimulates early growth and root formation, improves moisture and nutrient uptake and promotes optimum forage yield and quality. Phosphorus is immobile and will not leach or volatize. “It is subject to stratification and may build up in the top 2 to 3 inches of soil where it us not readily available to the roots.”

Potassium aids water use efficiency, increases disease resistance and improves cold hardiness. It also does not leach is not volatile.

“Potassium deficiency is uncommon in heavy soils and is more likely to occur in medium/coarse textured soils. Deficiencies may result in stand decline and winter kill.”

Maintain balance

Corriher said producers should stay on top of nutrient management for consistent production and emphasized that soils should maintain a balanced nutrient profile. She said some managers might try to decrease or eliminate one nutrient to save money. “But balance is important. Leaving out either one of the three primary nutrients will affect production, if soil test recommendations call for all three.”

Proper nitrogen application rates are important to meet production goals. With improved bermudagrass for hay production, Corriher said 100 pounds of nitrogen is needed per acre for each cutting. For grazing, 60 pounds of nitrogen per acre, applied up to three times a year may be necessary.

“To establish bermudagrass, apply 40 pounds of nitrogen per acre and after sprigs are established and growing, add another 50 pounds per acre to enhance establishment for one cutting the first year.”

She said improved bermudagrass, such as Tifton 85, may have “heavier nutrient demand because of higher yield and quality potential. Common bermuda or seeded bermudagrass may have lower fertility requirements but yield and quality will be lower.”

One application per year, at planting, should be sufficient for phosphorus and potassium. She recommends a split application of nitrogen to decrease nitrogen loss. “Split application increases yield by 5 percent to 10 percent and increase nutrient use efficiency by 25 percent to 30 percent. It’s also an advantage during extreme conditions.” Split applications reduce the risk of leaching, volatization, late freeze or drought.”

Corriher said current high fertilizer prices might tempt some producers to cut back on fertility. “Don’t eliminate one specific nutrient and rely on a soil analysis to get better information about what’s available and what can be reduced. If you must cut back, do so uniformly, not just one nutrient. Don’t apply just nitrogen if the analysis calls for nitrogen, phosphorus and potassium.”

She said soil pH plays a significant role in forage production and affects fertility rates. At a pH of 7, for instance, producers need 70 pounds of nitrogen, 30 pounds of phosphorus and 60 pounds of potassium. At 5.5, that changes to 52, 15 and 45.

Alternative sources

Producers looking to save money might also consider alternative sources, Corriher said. Animal manures may be an option, but she recommends testing to determine nutrient content.

She said beef cattle manure will average 27 pounds of nitrogen, 24 pounds of phosphorus and 36 pounds of potassium per ton. Dairy cattle manure averages 28, 11, and 26 pounds per ton. Broiler manure contains an average of 58 pounds of nitrogen, 51 pounds of phosphorus and 40 pounds of potassium per ton. Layer manure averages 30, 40 and 20 pounds per ton and swine manure provides 10, 9 and 7 pounds per ton, on average.

Corriher said these are averages and actual amounts vary. “Have it tested,” she said. “There is no guaranteed analysis.”

She said legumes may offer another nitrogen source for forage producers and provides added benefits. “Legume in forage may reduce or eliminate some commercial fertilizer,” she said. “Producers will still need phosphorus and potassium. They also get improved animal performance and may reduce winter feeding costs while improving soil tilth.”

Legumes also attract wildlife and help suppress weeds, which could reduce herbicide demand.

“But the best way to reduce cost is to soil test and calculate the cost per pound of nutrients, especially the three primary nutrients. If fertilizer and limestone are reduced, be prepared to lower stocking rates.”

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