As weather patterns change, some farmers are finding they are losing more nitrogen from their fertilizers to the surrounding environment. In many cases, this is due to increased and unseasonal rainfall followed by long dry spells and warmer winters. This year, we can attribute much of the volatile and unexpected weather to what the National Oceanic and Atmospheric Administration (NOAA) calls a shifting El Nino to La Nina pattern.
“If we look at the history of corn yields since we started keeping records in the 1860s, we have had four 25-year periods of highly variable corn yields because of variability in the weather,” says Elwynn Taylor, climatologist and agronomist at Iowa State University. “Those four periods were separated by four 18-year-long periods of consistent crop yields. I believe what we’re seeing is the beginning of a period of variable yields and weather.”
An increase in weather volatility means bacteria and other microorganisms can become more active earlier than normal, impacting not only crop performance but also nutrients moving off site.
“We might get this really warm weather that we usually don’t have where the soil temperature goes up into the 50s in December,” Taylor says. “Microorganisms in the soil can begin to convert nitrogen to a form that can be lost. Usually if you put on nitrogen in the fall, it will remain with the crop and not be lost to microorganisms in the winter months.”
Increased temperatures allow soil bacteria that contribute to nitrogen loss to be active for longer periods of time. Variability in rainfall may also play an increasing role in nitrogen loss, if we see heavy rains like we’ve had in some areas of the country the past couple of years.
A combination of these factors could increase the likelihood of nitrogen loss, which leads to reduced yields and increases the potential for disease pressure due to less vigorous plants. Lost nitrogen can end up in ground water if it leaches from the root zone as nitrate, or it can enter the air as ammonia.
As weather conditions remain uncertain, it’s important for farmers to talk to their local agronomist and create a nutrient plan that takes into account this volatility.