What’s the risk of nitrogen deficiency occurring in your cornfield? You can use the Iowa Soybean Association’s new online calculator to find out.
It’s no surprise that heavy spring rains are a primary risk factor for loss of nitrogen applied to Iowa cornfields, and later N deficiency in corn plants. Just how much risk there is for N loss on a particular field at a particular time, though, is difficult to get a handle on: rainfall, nitrogen rates, application forms and times all enter into the N loss and deficiency equation.
“It can be very difficult to pick out single causes of N deficiency when all these factors are interacting,” says Peter Kyveryga, director of analytics for the Iowa Soybean Association. “So we’ve done an analysis to isolate one factor to see how N deficiency compares when all other factors are kept equal. There’s no clear quantification of the four R’s for nitrogen management -- right source, right rate, at the right time, in the right place -- but adaptive nitrogen management based on post-season farmer feedback can tell you what you might expect.”
Online calculator lets you conduct “what if” scenarios
Kyveryga was a co-creator of ISA’s newly-developed online risk calculator, which can be used by an Iowa farmer to get a better sense of how N rate, rainfall, timing and form, plus previous crop can affect N management and risk of N deficiency. ISA has collected data on all those factors from about 3,500 cornfields across Iowa from 2006-2014 through its On-Farm Network and Environmental Programs and Services programs, and meshed it into equations within the calculator.
“You can check what is likely to happen with less nitrogen, or with more, early season rain, for instance,” Kyveryga says. “It’s really a learning tool as much as anything.”
Both rainfall and N rates impact the likelihood of N deficiency, but the calculator shows weather has a much stronger effect in N loss than the rate of N applied, he notes. Analysis built into the calculator shows fall-applied N required slightly higher N rates to reach optimal N status than spring applications.
You can use this calculator ahead of sidedressing N
“You can use the calculator ahead of sidedress to see what your risk of deficiency might be with various rates of N, checked against various rainfall amounts,” Kyveryga says. “Rainfall is always a key. Just one more inch of rain in May or June, holding all other factors constant, increases the probability of N deficient status by about 8% to 16%. The highest increase is in southern Iowa.”
“One thing we’ve seen is the risk of N deficiency is substantially higher in corn after soybeans vs. corn after corn -- from about 20% to 60% higher (the largest for northeastern Iowa) -- with all other factors being equal,” Kyveryga says.
“Our data also shows that, in general, starting with more N doesn’t rapidly decrease risk of N deficiency,” he adds. “Another conclusion drawn from historical data: fields in southern Iowa that received spring-applied anhydrous ammonia may have about 15% to 30% less chance to be deficient than other nitrogen form and timing combinations. Our data from 125 on-farm trials shows if you have an N-deficient stalk test, you have a 60% to 70% chance of a profitable yield if you apply an extra 50 pounds of N either in the spring or as sidedress.”
This new online nitrogen management tool is easy to use
Kyveryga urges farmers to use the calculator as a learning tool. “You select your location, crop rotation, N rate and your timing and form of N application,” Kyveryga says. “Then you select tabs for ‘Risk Based on Rainfall’, ‘Risk Based on Nitrogen Rate’ and ‘Rainfall Maps’ to see results based on your selections. You’ll get a graph and charts that show your risk based on past rainfall rates and N applications. If you want to see what your risk of deficiency would be with various other May-June rainfall amounts if you sidedress N at different rates, you can do those ‘what if’ scenarios and the graph will change.”
CALCULATING RISK: The Iowa Soybean Association’s Analytics Team has used data from 3,500 on-farm trials over 8 years to develop an online calculator that helps farmers assess risks of nitrogen deficiency.
An example of what the data and calculator show, Kyveryga points out, is that when all other factors are equal and the total N rates used by farmers range from 130 to 160 pounds of N per acre, corn after soybean fields in southern Iowa with 13 inches of May-June rainfall will have a 26% to 60% chance of late-season N deficiency; with 16 inches, a 40% to 70%; and with 19 inches, a 50% to 80% chance of N deficiency.
Based on data from large number of farmers from 2006 to 2015
“We started this analysis of our data about two years ago when the NRCS asked us to help farmers with adaptive management approach. Some farmers would use the end of season stalk test on their farms to assess N deficiency, but then they might not follow through to analyze the data to make changes in their nitrogen management,” Kyveryga says.
He adds, “Having data from a large number of farmers over a number of years can be helpful. We can’t predict rainfall, but we can check past rainfall and recent trends to try to establish the risk of loss of N when it’s too wet or too dry. With this calculator, we’ve tried to bring all the N management pieces together and quantify the outcome, expressed in risk management.”
To use the “Risk of Late-Season Nitrogen Deficiency” calculator, go online to isafarmnet.com and then select “nitrogen deficiency tool” on the left.
Lynn Betts is a regular contributor to Wallaces Farmer magazine.