While the state of Alabama has modified its corn nitrogen recommendations this year to reflect “anticipated yields,” the basics of fertilization still apply, says Charles Mitchell, Auburn University Extension agronomist.
“There are basic strategies for dealing with rising fertilizer prices,” says Mitchell.
“Soil testing is No. 1 — don’t put it out if you don’t need it. Also, use legumes to get nitrogen if you’re in a forage situation, and use poultry litter where you can. Use the least expensive source of nitrogen, or the most economical source for your situation, and recycle nutrients wherever you can.”
In the past, Alabama corn fertilization recommendations have not used anticipated yields, he says.
“I’d rather not use the term ‘yield goals’ because everyone has high yield goals. For irrigated corn, where you know you’ll have at least 180 pounds per acre anticipated yield and probably higher, we went with a standard recommendation of 200 pounds per acre, along with a little bit more phosphate and potash.
“If yield potential is greater than 200 bushels per acre, apply up to 1.25 pounds of nitrogen per bushel of anticipated yield in multiple applications,” he says.
It’s important, says Mitchell, to replace the nutrients you remove from the land. “If you take off a ton of hay, you’re going to take off 50 pounds of nitrogen, 10 pounds of phosphate, and 40 pounds of potash.
“If you’re removing that from the land, you’ve got to put it back on. That’s the basis of our recommendation for a hay crop. Very few people can make 8 tons, but if you make 8 tons, that’s 400 pounds of nitrogen, 80 pounds of phosphate, and 320 pounds of potash.”
Depending on what you’re growing corn for, you may or may not remove the whole plant, he says.
“If you’re just growing grain, corn grain is high in protein and you’re taking off a lot of nitrogen. With a yield of 180 bushels of corn per acre, you’re going to remove close to 180 pounds of nitrogen, and you’ve got to replace it. That’s where our 1 pound per bushel of anticipated yield comes from.
“We upped it to 1.25 because you don’t get 100 percent nitrogen use-efficiency. As yields get higher, use-efficiency goes down,” he says.
Organic matter’s role
Nitrogen is returned to the soil in the form of organic matter, says Mitchell. If you have very poor quality soil that is low in organic matter, you might have to compensate, and that’s not taken into account in a soil testing program, he adds.
“We’re going to look at possibly incorporating some soil quality or productivity index into our soil testing program in the future. We’ll start testing it this year to see if it’ll work.”
If you’re harvesting corn for grain, potassium is not a big concern because you’re recycling most of the potassium in the stalks and leaves, he says. When you’re removing corn grain, there are about 60 pounds of potassium in 180 bushels.
“There’s a lot of nitrogen and protein in cottonseed, so if you take off just lint, you’re not removing a lot. When we take off more than just lint, we take off seed which contains most of the nutrients.
“In a two-bale per-acre cotton crop, the standard recommendation would be about 90 to 120 pounds of nitrogen, depending upon the field.
“We’re actually putting on up to 120 pounds of nitrogen, but we’re only removing — in seed — about 60 pounds in two bales.
“Nitrogen management in cotton can be difficult, but it’s not related as much to yields as in corn. It’s very difficult to base nitrogen recommendations for cotton on yield potential.”
Potassium, on the other hand, gets recycled in the stalks and leaves, he says. “But on fine-textured, sandy soils, you might have to add potassium every year if your soils are testing low.”
Fertilizer prices — on the whole — have gone up and down in recent years and now seem to be trending back up, says Mitchell.
“Anhydrous ammonia remains the cheapest source of nitrogen available. Poultry litter is a good value, using an average value of 60 pounds of nitrogen per ton, 78 pounds of phosphate, and 56 pounds of potash.
“Just the nitrogen in chicken litter is worth $48 per ton if you can get it from the co-op for that price. I know some farmers in Alabama who are paying $70 per ton to have chicken litter spread, and they’re glad to get it.
“And phosphate is the most valuable component in chicken litter. We’re up to about $130 per ton value in chicken litter.”