Push yields to the max. Hold the line on fertilizer costs. Those concepts butt heads in these times of soaring input expenses.
Pay close attention to your fields, however, and you can make progress on both goals. The basics still work. Experts agree soil sampling remains a cornerstone of any well-managed cotton program. In fact, it may be more important now than ever.
"Historically, we have recommended soil sampling every three years. But with fertilizer prices at an all-time high, it may be of benefit to sample every two years,” says Darrin Dodds, Mississippi Extension cotton specialist.
"Growers with soils that test adequately for a nutrient may consider a maintenance fertilizer application compared to a fertilizer application to build soil nutrient levels,” Dodds says. "The goal of a maintenance application is to replace the fertility removed at harvest, not build soil fertility levels.”
Checking fertility levels more often may help keep yields up and costs as low as possible.
"With fertilizer prices as high as they are now, it makes no sense to apply a nutrient to a cotton field that is sufficient. In other words, for phosphorus (P) and potassium (K) fertilizers, a soil sample should be taken and P and K applied accordingly,” says Tom Barber, Arkansas Extension cotton specialist.
Let fertility programs coast too long, though, and yields will suffer.
"It's important to manage these programs carefully as we do not want to further deplete soil nutrients by applying less fertilizer than was removed by the crop,” Dodds says.
Don't just give fields a quick soil test, either. In Texas, for example, you may have to go deep for best results.
"You need a sound soil testing program, not just a surface level program. Look at the subsoil to see how much residual fertility you have,” says Randy Boman, Texas AgriLife Extension cotton specialist in Lubbock.
"Figure ways to get the soil sampled to at least 18" for nitrates. That isn't always easy. In the arid Great Plains states, our soils get dry and hard, especially in winter. If it stays dry November through January, you can have a real hard time getting probes in the ground,” Boman adds.
It can be trickier to trim nitrogen (N) costs than P and K. Since cotton uses little N prior to bloom, Barber says it could help efficiency to cut back on N applications during early growth stages and apply more just before bloom.
"Once cotton blooms it will require 3 lb. to 5 lb. of N and K per acre, depending on the boll load. By making applications closer to bloom we will effectively provide the fertilizer at the time the cotton is at peak demand for nutrients,” Barber says.
On-the-go sensors that apply N based on plant color can vary rates according to need, saving some money, says Gene Stevens, Missouri Extension agronomist.
"When you drive across the field, the sensors measure greenness and apply variable-rate N. The plant does not show the effect of low N until mid-square. From mid-square to first bloom is the window where this works best. Cotton doesn't really show yellowing colors until it gets to the early squaring reproductive stage,” Stevens says.
Using the sensors requires planning, however, which trips up some busy farmers, he says.
"One problem farmers have had when using on-the-go sensors is that they need a high-end reference strip. This is a strip where they apply an excessive amount of N, say 120 lb. per acre. Then, they can run the tractor sensor over the reference area and use it as a baseline,” Stevens explains.
Urease and nitrification inhibitors can help maximize fertilizer efficiency as well, says Glen Harris, Georgia Extension soils and fertilizer agronomist.
"I see them as another tool to increase efficiency in certain situations. For example, top-dressing granular urea in strip-tilled dryland with no rain in the forecast begs for a urease inhibitor. Nitrification inhibitors should help on sandy land with irrigation and above-normal rainfall,” Harris says.
"There are other materials coming out now that are designed to improve efficiency of P and K fertilizer, which will be great, but they are in the testing phase at this point.”
Reducing fertilizer sounds enticing but taking that step should be done only with great care.
"We've got a large number of farmers trying to cut back. The way they've been fertilizing irrigated fields in the past has been for the most part good. They think they could just cruise, but I don't want them to unless they soil sample. ‘Don't guess, soil test' is the old saying, and it's still true,” Boman says.
"Remember: N will be the driver for yield. Don't spend on P and K if you don't really need it. Go with what gives you the most bang for your buck: N,” he adds.
For help figuring your most profitable N rate based on commodity prices, visit a University of Missouri Delta Research Center Web site. It can be used for corn, rice and grain sorghum, as well as cotton. The Excel spreadsheet program is called NITROMAX. Go to http://plantsci.missouri.edu/deltacrops/Nitromax.html
Fertility management helps ensure you can push a cotton plant to its max from the beginning of the season to the end.
Photo by the author
Litter May Help Cut Costs
Chicken litter is a strong contender for Southern cotton growers hoping to cut fertilizer costs. It's abundant, and yields may, in fact, be enhanced when it's substituted for commercial fertilizer.
For five years, Sam Spruell, Mt. Hope, Ala., has applied two tons of litter per acre and averaged 700 lb. of lint per acre on 2,500 acres of non-irrigated cotton.
"We figure we get about 40 lb. of actual nitrogen (N) from each ton of litter. To be on the safe side, we sidedress with an additional 40 lb. of N. But we are at the point where we need no additional phosphorus (P) and very little potassium (K),” Spruell says.
He used to get broiler litter for the cost of cleaning out the chicken house. Demand increased, however, and trucking costs rose, as well. He now pays $25 to $30 per ton for litter, delivered and applied.
On average, broiler litter contains 60 lb. each of N and P and 40 lb. of K, says Charles Mitchell, Alabama Extension soils agronomist. Composition varies from one poultry farm to the next and from batch to batch, so litter nutrient levels should be tested before application.
At current fertilizer prices, the nutrients in the litter are worth almost $140 per ton, Mitchell says. The N alone is worth almost $40 per ton. Research indicates that less than two-thirds of the total N is available to the crop.
"Surprisingly, most Alabama research shows that, pound for pound, the total N in broiler litter is only slightly less effective as the N in ammonium nitrate fertilizer,” Mitchell says.
Some research shows better cotton performance with broiler litter. At the J. Phil Campbell Sr. Natural Resource Conservation Center in Watkinsville, Ga., scientists Dinku Endale and Harry Schomberg compared broiler litter with organic fertilizer in conventional and no-till cotton. They applied two tons of litter per acre.
"Just changing to no-till increased yields by 33% over conventional tillage. But no-till plus poultry litter fertilizer increased yield 42%,” Endale reports.
Research at the North Mississippi Research and Extension Center turned out positive results for litter, as well. Agronomist Haile Tewolde found that 3.5 tons of litter per acre outyielded 90 lb. of commercial N by 14% in no-till and 10% in conventional cotton.
Mitchell says no research shows high rates of broiler litter will reduce cotton yields or lead to excessive vegetative growth, late maturity or boll rot. It's important, though, to monitor N and P levels with regular soil tests, particularly where a shallow water table is present.
Treat broiler litter like commercial fertilizer, advises Charles Burmester, Alabama Extension agronomist.
Don't assume using litter will be cheaper than commercial fertilizer, either.
"We figure for fields that require P and K, broiler litter is still cost-effective, even at current prices. But where we've built up our P and K levels, it's getting harder to justify the cost for the N value alone,” says Alabama farmer Spruell.
---Written by Del Deterling
- September 2008