As discussed in the article “Climate change raises the stakes” starting on page 18, extreme weather events are happening more frequently. In situations of excessive rainfall, nitrogen losses can be exacerbated through three routes: runoff, leaching, and denitrification.
In a recent C.O.R.N. Newsletter published by The Ohio State University, authors Manbir Rakkar, Alexander Lindsey, Greg LaBarge, and Stephany Karhoff discussed these pathways of nitrogen loss. For runoff, fields with no residue or cover are more susceptible. If not incorporated, fertilizer applied to these fields before a heavy rainfall is likely to experience some degree of runoff.
Nitrogen can also be lost though leaching. The amount of loss depends on the amount of rain as well as the fertilizer used and the growth stage of the crop, the authors noted. Fertilizers that contain nitrogen in the nitrate form (such as UAN) are at greater risk for leaching. Similar to runoff, bare fields have more leaching potential. If a growing crop is on the field, nitrate leaching is less likely because of greater nitrogen uptake, they explained.
In saturated soils, nitrogen can be lost through denitrification, which is the conversion of nitrate into a gas form. “The amount of nitrogen loss depends on how long soil stays saturated and soil temperatures during water logging, with warmer temperatures accelerating the denitrification losses,” the experts shared. Potential denitrification losses under various conditions are shown in the table.
“If any of the above nitrogen loss mechanisms occur in your field, especially after a nitrogen fertilizer application was made, it is important to supplement nitrogen to the growing or upcoming crop to avoid yield losses,” the authors wrote.
To decide if additional nitrogen is needed, losses must be quantified. One strategy to estimate nitrogen losses is based on fertilizer type, timing of application, crop growth stage, and soil water content. A formula to calculate this can be found at bit.ly/cornnloss. Alternatively, a presidedress nitrogen test (PSNT) can be used to determine the nitrogen status of the soil.
Plants can also show signs of nitrogen deficiency. An inverted yellow “V” pattern on leaves or yellowing lower leaves may indicate nitrogen deficiency in a crop. If the symptoms remain after soils are no longer cool and waterlogged, it may be worth considering an application of side-dressed nitrogen, the authors advised.
This article appeared in the May 2024 issue of Journal of Nutrient Management on page 23. Not a subscriber? Click to get the print magazine.
