Richard Ferguson, Nebraska Extension soil scientist, recommends this newly revised publication from North Dakota State University. He notes this is “the best resource I’m aware of to provide concise information on products which can increase N use efficiency and reduce N loss to the environment.”

Nitrogen Extenders and Additives for Field Crops was written by Dave Franzen, North Dakota State University soil specialist, with input from soil scientists in the North Central Extension and Research Activity committee (NCERA-103), including Ferguson. The following is excerpted from this publication.

"Nitrogen management for crop production continues to be difficult due to transformations of N fertilizers when applied to soil and the uncertainities of weather, he writes. Nitrogen is lost from soil through the activity of soil bacterial transformation of ammonium to nitrate, and from nitrate, the N can be lost leaching or denitrification. There are chemistries available that inhibit the transformation of ammonium to nitrate, and there are also compounds that inhibit urease enzyme activity, decreasing the risk of ammonia volatility.

Understanding nitrogen extenders and additives and how they perform under various scenarios can help ensure you select one that best fits your operation.

Franzen writes: “Nitrogen often is applied to crops in the north-central region of the U.S. before planting. During the first four to six weeks after planting, corn requires only about 5 percent of the N applied. The following two to four weeks of growth require a large proportion of the total seasonal N requirement because the rate of N uptake dramatically increases past the V6 growth stage.”

“In winter wheat, low levels of plant-available N are required for overwintering. However, once wheat breaks dormancy, a large proportion of N uptake occurs during the next few weeks.

“To increase N use efficiency, by increased yields or decreased N rates, a number of products have been developed to delay the N transformation process so that the period of time in which the N source remains available for uptake is close to the time of maximum N uptake. These products can be classified into the following groups:

• nitrification inhibitors, including nitrapyrin and dicyandiamide products,
• urease inhibitors,
• combined nitrification and urease inhibitors, and
• slow release N products.

This publication discusses products in each of these categories, including their attributes, performance, and crop yield response in various trials, and reviews research findings from land grant universities, including the University of Nebraska-Lincoln. It also includes information on poly-coated urea and related product research.

Nitrogen extenders and additives add costs to a farming operation. Understanding product attributes and how they perform in various soils should be considered in product selection. To ensure you’re getting value for your investment, Franzen writes “… producers need to give careful thought to selecting the product appropriate for a specific field. In addition, when considering products not explained in this publication, look for independent field trials, preferably conducted by land-grant university researchers, to verify effectiveness and mode of action.”

Read the full discussion in Nitrogen Extenders and Additives for Field Crops (NDSU SF1581).