Two FFA members from different parts of the state are talking about nitrogen rates for corn used on their farms. One insists that his dad doesn’t like to waste money, so 220 pounds per acre must be the right rate. The other says his dad only applies 180 pounds per acre and gets top yields most years. Who is correct?
The simple answer is that they both could be right. Bob Nielsen and Jim Camberato, Purdue University Extension agronomists, determined after nearly a decade of testing that the best recommended N rate for economic optimum yield depends upon several factors, including where you farm and your soil types. Cost of nitrogen and price of grain also factor into the equation.
Corey Gerber, director of the Purdue Crop Diagnostic Training and Research Center, incorporated their work into a nitrogen rate calculator in the new Corn Field Scout app for iPhones and Android cellphones, available for minimal cost at the app store.
Here are recommendations for a specific example in each of Indiana’s nine crop-reporting districts. In each case a farmer will apply anhydrous ammonia; price of anhydrous is $400 per ton, and corn is $3.50 per bushel. Soils are assumed to be medium- or fine-textured, not sands. The example is also for rotation corn.
• Northwest Indiana. Perhaps you live in Porter County. Plug in $400 per ton of ammonia as the N source and $3.50 for corn. The calculator pegs the optimum economic rate at 194 pounds of actual N per acre.
• North-central Indiana. Maybe you farm near Winamac but are fortunate enough to have medium-textured soils. The recommended rate based on Nielsen and Camberato’s work is still 194 pounds of N per acre.
• Northeast Indiana. Suppose your farm is near Columbia City. Your soil types are different than those farther west. So is your N recommendation: It’s 238 pounds per acre.
• West-central Indiana. What does your N rate look like if you farm near Crawfordsville? This area of the state has one of the lowest recommendations. For these parameters, it’s 188 pounds per acre.
• Central Indiana. Suppose someone farms in Hendricks County. If he uses the cellphone app calculator, what N rate will be recommended in this situation? The rate is 213 pounds per acre.
• East-central Indiana. What about someone who farms in Wayne County? If he plugs in $400-per-ton ammonia and $3.50-per-bushel corn, the calculator recommends 232 pounds of N per acre. Northeast and east-central Indiana typically require the highest rates, Nielsen and Camberato determined.
• Southwest Indiana. If you farm in Knox County on medium-textured soils, your recommended rate in this example is 188 pounds per acre, the same as in west-central Indiana.
• South-central Indiana. Maybe you farm in Bartholomew County. The recommended rate in this example is again 188 pounds per acre.
• Southeast Indiana. A farmer in Ripley County would also see 188 pounds per acre pop up in the calculator.