This year, fields with flooded areas are fairly commonplace in certain parts of the country that have been plagued by heavy rains over the spring and summer. There are the obvious challenges and decisions that need to be made about planting and replanting damaged crops, but there are also some concerns about nutrient loss.

Fields that have received a lot of rain could have stunted plants or uneven growth. Does this mean the plants are lacking nitrogen, sulfur, and just oxygen?

“A lack of oxygen can mimic nutrient management deficiency,” said University of Minnesota Extension researcher Jeff Vetsch in a “Strategic Farming: Field Notes” podcast. “Sometimes it is hard to know.”

In terms of nitrogen loss, Vetsch said denitrification, which is the conversion of nitrate to nitrogen gas, is a driving factor in wet conditions. At his home base in southern Minnesota, some locations had close to 10 inches of rain in a week. He predicted that some of these areas may have lost up to 50% of the available nitrogen due to denitrification and leaching.

Supplemental nitrogen may be needed, but Vetsch noted that in their years of research, more than 40 to 50 pounds per acre is rarely needed. This year could be an exception, though, potentially requiring 60 to 70 pounds of supplemental nitrogen per acre, especially on fields planted to corn following corn.

Fields experiencing the most nitrogen loss are those that had manure applied in the fall. Application of other nitrogen sources or anhydrous ammonium in the fall would also be more susceptible. However, enough time has passed that Vetsch said almost any applied nitrogen, except for sidedressed nitrogen, could be affected by the conversion of ammonium to nitrate-nitrogen nitrification and lost. “I don’t think there’s any one source that’s safe; even spring applications of ammonia probably still saw some significant loss,” said Vetsch.

This nitrogen can be dribbled or applied using y-drops. If the ability to apply with wide drops is not available, he said rubber hoses can be attached to the nozzles. They will dangle between the rows while driving down the field with the manure dribbling out of the hose.

Ideally, these rescue treatments are applied to growing corn by the V6 or V8 stage, but Vetsch said it can still be beneficial up to the V14 stage. Once plants get to tasseling and beyond, the return on investment becomes less certain, he noted.

Extreme rainfall can cause erosion on fields used to grow feed for livestock, but Vetsch said it also enhances the risk of compaction. “It’s amazing how this rainfall can compact soils,” he noted. “Fields are very hard, and that really hurts infiltration when we get more rain in the days to come.” When applying supplemental nitrogen or other nutrients, be aware of this risk caused by wet conditions and take steps to reduce compaction when possible.