Efficient fertilizer use helps beat high prices

Farmers in the Southeast had a to take a hard look at fall wheat planting, not because of bad weather or any other production-limiting factors, rather because of the high cost of fertilizers needed to grow the crop.

As farmers plan their 2009 crops, the same process of elimination will be used to figure out which crops in which fields will produce the most optimum crop for the most optimum value using the least amount of fertilizer.

Wise use is a good thing, but simply cutting back on fertilizer can be a very bad thing, cautions Virginia Tech Soil Scientist Mark Alley.

Speaking at the recent Virginia Ag Expo, Alley says, “phosphorus is a good place to start when looking at ways to conserve fertilizer costs. In the upper Southeast growers have often built P levels so high that getting any yield increase from phosphorus is unlikely.

“Now, is a good time to live a couple of years off past good fertility practices when it comes to phosphorus use,” he adds.

When it comes to potassium, world demand has driven a very large price increase. Potassium magnesium sulfate is not so much of a worldwide commodity and the price has not gone up in price as much as other sources of potassium.

“In the past many of our farmers got the sulfur they needed from ammonium sulfate. Now, growers will have an opportunity to get sulfur from potassium magnesium sulfate and possibly reduce the overall cost of fertilizer,” says Alley.

“Soil testing is more important than ever before in terms of cost,” Alley says. “Potash should be used in fields testing low and not used in fields higher in P — the overall impact should be to lower input costs,” he adds.

Though not as sharply as phosphorous and potassium, nitrogen costs have gone up steeply over the past two years.

One impact was the spring 2008 move by China to impose a 140 percent tariff on all nitrogen fertilizers leaving that country. There is no doubt the Chinese tariff contributed to the summer-time spike in nitrogen prices.

The bottom line, says Alley, is that growers have to be more efficient in the way they use nitrogen to continue to take advantage of high commodity prices.

Growers need to understand they lose nitrogen by volatilization, particularly from urea, from runoff from heavy rains, from immobilization when N is tied up in residue, and by leaching. With N at a record high price, the question is how to avoid these losses?

Alley says most N loss can be avoided by avoiding surface applications. Simply putting the N under the soil limits immobilization and eliminates runoff and volatilization.

“When we were paying 19 cents a pound, it didn’t make much difference whether you put it on top or under the soil. We typically just mixed in some weed control, put out the N and went on to work on something else. With today’s prices that’s just not possible,” Alley says.

“For corn, we’ve seen growers go with 50 pounds of N in the starter band, placed two inches by two inches, and that has worked well. Other growers have tweaked that system to a 3 X 2 inch band and upped the N to 60 pounds per acre. Both systems have worked well for Virginia growers,” he adds.

“Banding avoids most of the loss mechanisms, plus it gives you a wide window for side-dress applications. Some growers don’t like handling so many gallons on the planter, but it is a trade off for flexibility of timing side-dress applications.”

For phosphorus, growers can mix it with N in the starter band. In many cases a 3:1 mixture is enough phosphorus. Historically, the ratio went the other way with more P than N, but Alley notes that in most soils in the upper Southeast that ratio is backward to what the soil actually needs.

“We are now looking at ways to inject side-dress N into the soil. We looked at 91, 111 and 130 pounds of N side-dressed. We compared dribble between the rows, which is the common practice for most corn growers, with injection of reduced rates,” Alley says. Two Red Ball injector systems were used in Virginia to apply the subsoil nitrogen.

Paul Davis, Virginia Tech Extension Coordinator in New Kent County, and a long-time proponent of never-till systems, says the new injection systems being tested in Virginia do slow down application of nitrogen, but the tradeoff is lower rates, higher efficiency and ultimately lower cost to the farmer.

Typically, surface applied nitrogen is applied 24 rows at a time and moving 9-10 miles per hour. By comparison, the injection rig covers 12 rows and at the most at 7-8 miles per hour.

At a cost of 90 cents per pound of N, subsurface application of nitrogen is well worth the extra cost and time. Davis points out that a high percentage of grain farmers in central Virginia have been in no-till systems for 10-20 years, leaving a lot of residue on top of the soil. In addition, many growers are adding cover crops, which after burn-down, leaves more residue to tie up fertilizer.

“In many cases by side-dress time, our growers can’t even see the soil,” Davis says. “So, we want to cut through these layers of residue and get N into the soil. We know we can cut back some on rates, but we don’t know how much. Five locations in Virginia should provide some answers as to rate reductions versus yield loss on various grain crops,” he adds.

“Growers need to remember that once they see corn leaves lapping the middle of the rows, the roots are also lapping. So, getting close at side-dress is not so critical,” Mark Alley stresses.

“The other thing we like about these Red Ball applicators is the coulter that allows us to get nitrogen through this residue and into the mineral soil. A sharp coulter is critical, but most farmers have equipment on the tank to make a coulter that will work just fine,” he says.

“The only time we had problems was injecting N into a rye cover crop early in the morning. The residue was still wet and it did clog one of the injectors. When the residue is dry, we’ve had no problems getting N into the soil,” Paul Davis adds.

“We may one day have to grow our own nitrogen. Before it comes to that, just to stay profitable, growers need to look at some alternative ways to apply fertilizer to optimize utilization by the crop and minimize losses to natural occurrences,” Davis says.

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TAGS: Management
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