Extensive research in Alabama on wheat fertilization has shown there’s no “one size fits all” nitrogen recommendation, with varying rates and timing depending on your soil type and location in the state, says Kip Balkcom, research agronomist with the National Soil Dynamics Laboratory in Auburn, Ala.
The research began in north Alabama’s Tennessee Valley where many growers were shifting to more intensive wheat production practices, said Balkcom, speaking at a recent meeting of crop consultants in Auburn.
“Growers were trying to maximize their wheat yields with different management practices,” says Balkcom.
“They were planting into existing crop residue, eliminating that one trip across the field. They also were planting higher seeding rates with higher nitrogen levels, so people were concerned. We evaluated nitrogen rates and timing across different production systems.”
Research was conducted for 12 site-years, from one end of Alabama to the other, he says, and with varying nitrogen rates.
“We had three rates of nitrogen, using 60, 90 and 120 pounds of nitrogen per acre, but we applied it at different times and different splits. We chose 20 pounds at fall because that is the current Auburn University recommendation.
“If you put on too much nitrogen in the fall, there will be excess growth, increasing the potential for winter kill,” says Balkcom.
Wheat, like corn grain, requires about 1 to 1.5 pounds total nitrogen per bushel of anticipated yield, he says. Because of its transient nature in the environment, nitrogen fertilization of wheat is the most difficult nutrient to manage, but also one of the most critical because it is an essential component of protein.
Nitrogen produces green, leafy growth, and supplying adequate nitrogen in the fall is necessary for good plant establishment. Once the weather becomes cold in December, wheat makes very little green, leafy growth until the weather warms in late winter.
“Excess nitrogen applied in the late fall is a waste of an expensive resource and can cut into profits. It also could be leached from the soil by winter rainfall and could be unavailable in the early spring when the crop needs it for rapid growth.”
Wheat for grain only
This extensive research has resulted in Auburn University recommendations that call for 20 pounds of nitrogen per acre at fall planting on Coastal Plain soils if wheat is grown for grain only.
Limestone Valley soils are less responsive to fall-applied nitrogen.
“If wheat is following a heavily fertilized corn crop, a good peanut or soybean crop, or a drought-damaged crop that could not utilize all of the nitrogen applied, then often no additional fall nitrogen will be needed on wheat for grain.
“If wheat is to be grazed or if more fall growth is desired and is possible, then up to 100 pounds of nitrogen per acre should be applied in the fall,” according to the recommendations.
The remainder of the nitrogen (60 to 100 pounds per acre) should be applied at Feeke’s growth stage 4 or about mid-February in south Alabama.
In north Alabama, nitrogen should be applied between Feeke’s stages 4 through 6, with Feeke’s stage 6 being at about mid-March.
The complement of nitrogen can be applied in split applications if desired and a high yield potential exists (80-plus bushels per acre).
In south Alabama, where spring temperatures rise dramatically, wheat develops rapidly, and nitrogen must be available during this rapid period of green, leafy growth.
“Afterwards, heading and ripening also occur quickly, and there is not enough time for split nitrogen applications.
“In north Alabama, where cooler springs may prevail, wheat develops slower over a longer period of time. This also may be conducive to higher yields if nitrogen is available throughout this period. “Therefore, split nitrogen applications may be desirable for high yielding wheat in north Alabama,” according to recommendations.
Research has found no wheat yield increase to splitting nitrogen fertilizer rates when wheat was planted following cotton.
The main concern with over-application of early spring nitrogen is the potential for lodging and possible freeze damage in northern Alabama.
Looking at the effect of other nutrients on wheat, Balkcom says low phosphorus levels can be detrimental.
“We had 40 percent of the top yield of 52 bushels per acre when phosphorus was deficient. We take a hit with deficient potassium levels, but it’s not as detrimental.”
The easiest way to guard against deficiencies is with soil-testing, he says.
“It’s easy to take a soil test and then fertilize accordingly. Where we had no sulfur and no micronutrients, there was no effect on wheat. The major things we need to be concerned with as far as wheat goes are nitrogen, phosphorus, potassium and pH.”