With fertilizer prices leading the way for increased farming input costs, farmers are looking for strategies that’ll help them maintain nutrient levels while keeping expenses at a minimum.
Long-term plots at Auburn University show winter legumes can go a long way in providing adequate nitrogen for a high-yielding cotton crop.
“Just two years ago, we were talking about $300-per-ton nitrate urea, and now it’s out of sight,” says Charles Mitchell, Auburn University soil fertility specialist. “Some fertilizer prices have dropped significantly since mid-summer of last year when we reached an all-time high. Urea was costing more than ammonium nitrate in our part of the country, and that has never happened before.”
The important thing for producers, is to look at the cost-per-pound of nutrient, says Mitchell. “Don’t worry about the cost per ton – look at the cost per pound.
“We’ve come up with four strategies that can be used by producers in Alabama to help manage fertility costs. They are very narrow strategies, and they are tools we already have at our disposal,” he says.
With 25 years of experience, Mitchell says he probably looks more toward what has been done in the past to guide future strategies.
“One of these strategies is soil testing and the technology supporting soil testing. Another is using legumes as a cover crop. In addition, in the Southeast, poultry litter is a huge source of nutrients. When I first started working in Alabama – up until about two years ago – a big part of my job was talking about the problem we have with excess poultry litter. But we haven’t talked about it in two years. We’re using every ton we can get in Alabama.
“Finally, a good strategy is to use the least expensive source of nitrogen (N) whenever possible,” he says.
Mitchell advises growers to pay attention to soil test results. But, more importantly, pay attention to where the calibration was done. “If you’re living in Arkansas, and you use a laboratory on the East Coast, make sure those calibrations are for Arkansas crops and soils. Once you get beyond a critical value for a specific soil type – whether it’s 25 parts per billion in Alabama or 30 parts per billion in South Carolina – the probability of seeing a response to added phosphorus (P) is very low. If your soils are testing in the high or very high range, save your money. Phosphorus is the most expensive nutrient we could have applied in the past year. If you don’t need it and the probability of response is low, don’t put it out there,” says Mitchell.
If you’re using precision agriculture, and you’re basing your applications on faulty soil test results, you’re wasting a lot of money, he says.
Some growers want to know that if their soil test shows they don’t need P, and they don’t apply any for the next year or two, will there be long-term implications, says Mitchell.
“In our experiment, fertilizer P was applied at different rates up until 1982, and then for 15 years, no additional P was applied to those plants. We monitored the plots and planted cotton, corn, wheat and soybeans over 15 years. Soil-test P did not change over that 15-year period – it was still testing high. We saw the same thing with potassium (K). It was testing high for K in 1982, but by 1996, we had to start re-applying K.
“Last year, in our ‘Old Rotation’ trial at Auburn University – the oldest continuous cotton study in the world – we ran into some potassium problems, after 110 years. The bottom line was that the crop produced 1,940 lbs. lint/acre where we irrigated last year. We had the potash deficiency because of our high yield potential. A little extra K may have pushed yield up to 4 bales/acre – we don’t know.”
Turning to the second strategy, Mitchell says the “Old Rotation” also offered some valuable lessons on the use of legumes as winter cover crops. “This trial was started in 1896, primarily to look at what would be required to make cotton sustainable on the highly erodible, low-fertility soils of the Southeast. It included plots with and without winter legumes. We have been monitoring these for more than 110 years now. I can say you can grow a good cotton crop in the Southeastern U.S. using only winter legume N. Where we had no N and no legume, we were getting about 301 lbs. lint/acre. When we add crimson clover or vetch, we can boost that yield to a little more than 2 bales/acre. When we add about 120 lbs. N/acre, we boost our yields by about 50 lbs./acre over the legumes by themselves.”
It can safely be said, he says, that the legume cover crop adds the equivalent of 120 lbs. N/acre.
“Whenever you have a good cover crop, it increases your yield potential because it offers increased soil organic matter and other factors, like water-use efficiency. I tell our producers that the additional management required by winter legumes is not easy, and it’s not something you can change overnight on 2,000 acres of cotton. But it does work and it is an alternative.”
Another fertilizer option for growers in Alabama is using poultry litter, says Mitchell. Sixty-two percent of Alabama’s farm economy is now based upon poultry production, he adds, with the state producing about twice as many tons of poultry litter as fertilizer that is used.
“We grow cotton in all areas of Alabama. But these cotton fields are in fairly close proximity to our broiler production areas. With high fertilizer prices over the past two years, every ton of poultry litter that’s available is being used by our farmers. They have learned the hard way that it is an alternative source of nutrients.”
Mitchell says he has been telling producers that dry chicken litter, as it comes out of the houses, is about a 3-3-2 fertilizer. “We’ve seen it go up because chicken producers are keeping litter in the houses for longer periods of time, and the P is building to higher levels. In some areas, we’re seeing that N is being built up to higher levels because of management. At current fertilizer prices, the value per ton of chicken litter is about $124. In poultry-producing states, you can have litter spread for $40-70/ton. That’s a bargain, especially if you need that P.”
About two-thirds of the N in poultry litter is available in the year it is spread, he says.
It’s also important, says Mitchell, that growers use the least expensive source of N.