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:

  • The amount of runoff and erosion from the land. This is determined by the amount of precipitation and intensity of rainfall events, slope steepness and length, soil type, crops grown, and management practices.

  • Distance to concentrated water flow or to surface waters. Most of the nitrogen that enters surface waters comes from areas that are near a concentrated water flow. Therefore, fertilizer or manure nitrogen applied within 50 feet of concentrated water flow is more likely to enter surface waters than for N applied more than 100 feet away.

  • Whether there are any management practices in place to trap sediments and nutrients carried by runoff and erosion before these enter surface waters. Vegetative filter strips and buffer zones along streams are effective in filtering sediments and nutrients from erosion and runoff to reduce the amounts entering surface waters.

    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:

  • Use tillage practices that minimize the potential for nitrogen loss in runoff and erosion.

  • Use the right amount of nitrogen fertilizer. Credit needs to be given to nitrogen from previous legume crops, manure applications, and irrigation water. Guidelines are available for each state for determining the nitrogen application rate.

  • Avoid surface application of nitrogen in spring. There tend to be more intense storms in the spring than at other times of the year, and this is when there is the greatest risk for nitrogen loss to surface waters.

  • 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.