WISCONSIN DELLS — Farmers who think they’re applying nitrogen fertilizer at recommended rates could still be leaving a surplus of environmentally risky nitrogen on their fields, a University of Kentucky professor said Dec. 12 at the UW Discovery Farms Conference.
Josh McGrath, an associate professor and soil management specialist at the University of Kentucky, talked about “Navigating nutrients in a world of competing interests” to kick off the Discovery Farms Conference.
McGrath said nitrogen recommendations are generally based on average yields on a particular field. But every year, those recommendations are wrong, he said, because yields and plant uptake are always different.
The nitrogen left over after plant uptake is at risk to run off into waterways, McGrath said.
“There are certainly fields where (farmers are) applying (nitrogen) beyond recommendations,” he said. “But I’m saying even if you’re following the recommendations, you’re still leaving a surplus of environmentally risky nitrogen on the field, because we can’t always determine the right rate.”
In most farmers’ eyes, the penalty for underfertilizing is greater than the penalty for overfertilizing, because nitrogen is worth less than corn, he said. Therefore, farmers tend to apply above the economic optimum of nitrogen.
“We need new methods for rate decisions,” McGrath said. “Our technology for making recommendations is old. We have yield monitors, sensors and all this machinery, but the problem is we have made all these hammers, and nobody has taught us how to swing the hammer.”
When it comes to phosphorus, less than 15 percent of the phosphorus applied to fields is available in the first year, McGrath said. Less than 5 percent of applied phosphorus is generally lost, but that can still be well beyond the environmentally critical value.
McGrath said it is often difficult to manage nitrogen and phosphorus with yield, economic returns and environmental loss all in mind at the same time, but yet it is important to do so.
Amber Radatz, co-director of the Discovery Farms Program, said the program has used data from 40 farms across Wisconsin to study the interaction between manure and field management. She said how manure is managed will undoubtedly impact most farmers futures.
“If you’re not thinking about how to environmentally check the boxes with manure, I think that’s going to present a lot of challenges with your future farm,” she said. “You can’t choose one or the other, agronomically or environmentally. Farmers are trying to make those two things match, and we are here to provide science and tools to help you with that.”
Every farm and every management system has an area where the farm’s environmental impact could be improved, Radatz said.
In Wisconsin, runoff is going to happen on some farms every year, and how farms manage their farms can control what’s in that runoff material, she said.
Studies have shown that March is the month in which the most runoff occurs, while February, April, May and June can also be problematic. On average 92 percent of the runoff occurs during those five months.
“If we’re looking to prioritize, that’s where we’re going to do it,” Radatz said of those months.
February and March are the months when farmers “have to be on their game.” They have to know the best timing for applying manure when it will have the least amount of environmental impact.
“You need to try to apply manure close to when the plant needs it and not close to when a runoff event is likely,” she said.
Incorporation of manure can be important on fields that are most susceptible to runoff, Radatz said.
“If you are only spreading it on the surface, the only thing liable to get it is water moving across the surface,” she said. “Nutrients should be placed below the surface but not with so much disturbance that soil losses become an issue.”
Nutrient crediting from manure is kind of like online shopping — you put in your order and wait for it to arrive, Radatz said.
“When you put it out there, if you’re not sure it’s there, maybe let’s not put another order out, but investigate it further,” she said. “There is an opportunity for manure users to take another look at crediting and save on fertilizer purchases. If you have manure out there and then you buy extra fertilizer, and you’re the guy paying the bill, that really sucks.”
Radatz suggested using nutrient crediting for all sources, testing the soil and developing realistic yield goals, and adjusting nutrient applications accordingly.
“There isn’t much of a (profit) margin (raising crops) right now, so let’s maximize the efficiency of what we’ve got where we’ve got it,” she said.