Caution advised for cotton fertility changes

With fertilizer prices shooting through the roof, many farmers may be looking for cheaper alternatives this year. Some may consider cutting back on nutrient recommendations; some may look for different sources of commercial fertilizers, and a few may consider organic materials.

Be cautious, advises Kevin Bronson, Texas Extension fertility specialist, Lubbock.

Bronson says farmers are showing interest in organic fertilizers, mostly cattle manure from feedlots and dairies in the High Plains, and, even if those materials provide some long-term benefits to the soil, growers should make certain they know what they’re getting, he says.

“Composted manure (typically air-dried) adds organic matter to our soils and improves water-holding capacity,” Bronson says. “Our soils are typically low in organic matter.”

But consistency and concentration may be an issue. “Manure is high in phosphorus, often a one-to-one or two-to-one ratio with nitrogen. Plants like a three-to-one to five-to-one ratio.”

He says manure tends to turn soil rich in phosphorus quickly. That may not be as big an issue in the flat and arid High Plains as it is in the rolling, more humid Mid-South or Southeast. “We have relatively flat fields and no significant surface water and a lot of farmers use conservation tillage techniques. Still we can reach a point where we should not add more phosphorus.”

He says manure analysis is also variable with uneven release into the soil. “It is important that a farmer test the material at a soil lab the same as he would with a soil sample. He has to identify the amount of phosphorus, and nitrogen. He can’t afford to work in the dark.”

Bronson says even with a good analysis, farmers still may not know how much of each nutrient will be available the first year. “Release factors vary,” he says, “and are unpredictable.”

He says in some cases manure may not release much nutrient the first year and then more in subsequent years. “And sometimes just the opposite is true. It’s possible to reach a nutrient deficiency quickly.”

Bronson figures problems with organic fertilizers will be minimal in the High Plains. “Folks who have it get rid of it quickly,” he says. “There is not enough to go around. The supply is nowhere close to what we would need for 4 million acres of cotton and all the grain in the area.”

Transportation costs from other areas would likely be prohibitive, he says. The volume of material necessary, the concentration of nutrients, the variability of release and potential cost of transportation are factors that limit use.

Bronson says farmers are also looking at alternative sources for commercial fertilizers. “Traditionally, solid fertilizer has been cheaper than liquid.” That’s not the case this year. Recent prices show dry fertilizer at near $600 a ton in the High Plains with liquid (32-0-0) at $420 a ton.

“That’s 65 cents a pound for nitrogen,” Bronson says, “an all-time high. Nitrogen prices are up like crazy. Phosphorus is also up but not that much.”

He says farmers are using more urea and less anhydrous. “Anhydrous is cheaper if they can get it on. Even if farmers do not have their own application equipment and have to have it custom applied, figures show an advantage with anhydrous over 32-0-0.”

He says a few farmers north of Lubbock use anhydrous but says “it’s rare to see it south of Lubbock.”

As farmers look for way to manage soaring fertility costs Bronson recommends the basic principle of nutrient management. “I still don’t see enough soil testing. Farmers don’t soil test frequently enough and they tend to apply a little rich.”

He’s been working at the Lubbock Research and Extension Station for ten years and says in 1999, when nitrogen was 20 cents a pound, farmers had little interest in fertility. “Price was cheap, cotton was a relatively low-input crop, and they tended to go a little rich (with fertilizer rates).

“Now, they’re not making insurance applications. If a soil test calls for only a small amount of a minor nutrient, they often leave it out.”

He says Texas A&M provides a good role in soil fertility management. “We offer non-biased recommendations. If a farmer wants to check his soil fertility, we can help.”

He says farmers who have been using a bit more fertilizer than A&M recommendations may be able to save money by cutting back a bit. But he cautions against dropping below recommended rates.

“Returns will be down this year because of higher fertilizer prices,” he says. “The same is true because of diesel prices. It costs more money to go across the field. But cutting fertility below good recommendations will reduce returns even more.”

More reasons to soil test. “Don’t go into the season blind without a soil test.”

Bronson says some farmers follow a fertility program, without testing. “They should run their own field trials. Leave a swath and use a different nutrient program and see the difference.”

He says on-farm tests are important for farmers. “Their field conditions are different.”

Soil test recommendations are not foolproof. “We deal in probabilities, but the odds are that following good recommendations will help. If a soil test is low the probability is that following recommendations will increase yield potential. With a high soil test we have less probability of a yield response.”

Soil tests last year were of somewhat limited value, for instance. “We had a lot of rain and a lot of nutrient leached out of the profile. Still, a soil test is better than nothing.”

He says nitrogen is the most important nutrient, followed by phosphorus. Zinc comes in a distant third and may not be necessary every year. He says sulfur is not usually needed.

Iron may be necessary on caliche soils. “Don’t plant peanuts, milo or soybeans on these soils,” Bronson says. He says farmers don’t have a good chelate source of iron for caliche soils. “It exists but it is too expensive for row crops. We do have good chelate sources for zinc.

“Typically, we don’t need potassium, but if fields have produced high yields, 200-bushel corn or 3-bale cotton, for three years in a row, check potassium. See if the soil needs it. High yields may draw down potassium levels.”

The basic management program for any nutrient source has to know what’s in the soil, Bronson says.

email: [email protected]

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