MANHATTAN, Kan. -- Producers may be planning to topdress nitrogen on wheat this winter while the ground is still firm and frozen, and before soils become too wet to accommodate fertilizer applicators.
This practice, however, should be avoided, said Dan Devlin, Kansas State University environmental quality scientist.
Nitrogen should not be applied to frozen soils because of the potential for surface runoff, Devlin said.
"When nitrogen is applied to frozen soils, it remains on the soil surface and on crop residue until the ground has thawed and precipitation moves the nitrogen into the soil," explained the agronomist, who is a specialist with K-State Research and Extension.
"If precipitation falls while the soil is still frozen, a high percentage of it could move off the field in runoff water and into nearby surface waters. This causes nitrogen contamination of surface waters, one of the major water pollution concerns in Kansas and nationwide."
Agricultural lands are the source of much of the nitrogen entering surface waters, according to research nationally.
"The nitrogen may be in inorganic forms, primarily ammonium and nitrate ions, and organic forms. Inorganic forms are most immediately available to aquatic vegetation, but much of the organic nitrogen becomes available over time," Devlin said.
Nitrogen transport to surface waters is largely determined by several factors, he said, including:
Much of the sediment-bound nitrogen can be retained in sedimentation basins and wetlands preventing entry to surface waters.
In addition to avoiding nitrogen applications on frozen ground, Devlin said that several management options may be considered to minimize nitrogen runoff losses:
When surface waters are enriched with nitrogen or phosphorus, excessive growth of algae and other aquatic vegetation can occur, Devlin said. This vegetation growth depletes the oxygen concentration in the water.
"When the vegetative mass dies and decomposes, oxygen is further depleted and compounds toxic to other aquatic life may be released resulting in eutrophication. Nitrogen in surface waters moves easily in the flow of water in streams and rivers. Much of that in the Mississippi River watershed eventually reaches the Gulf of Mexico where it contributes to the 'dead zone' or the condition of hypoxia," he said.
SOURCE: K-State Research and Extension news release.