Does your preseason strategy always work out perfectly? Typically, one or more things related to nitrogen management don’t go according to script. When that happens, what can you learn?
Here are two scenarios from Midwest farm fields. Dan Quinn and Mark Licht offer insights. Quinn is the Purdue Extension corn specialist. Licht is an Extension cropping systems specialist at Iowa State University.
Scenario 1
We applied 120 pounds per acre of nitrogen before planting. Our stand is only 26,000 plants per acre now. We were going to side-dress an additional 60 pounds of N. With low corn prices, should we go ahead, cut back or skip it altogether?
Quinn: A corn stand of 26,000 plants per acre, although low, can still have high yield potential. I would not cut back on the N rate. Sidedress the additional 60 pounds of N per acre, or at least apply enough to equal the recommended amount for your location.
Licht: Conduct a late-spring nitrate soil test to determine soil nitrate values. Ideally, you could combine that information with a couple of check strips where you have added some additional nitrogen. This will give you a leaf color comparison. Remember that leaf chlorophyll is a good indicator of N sufficiency or deficiency.
If higher N application strips are darker green, it is a good indicator that additional N will be needed. Overall, my guess is that 26,000 plants per acre will not need a full N application rate. There are fewer plants competing for available nitrogen.
Scenario 2
We have 100 pounds of N applied and achieved 32,000 plants per acre. How much more N should we apply based on corn price and N price? Does form of N matter?
Quinn: This will largely be dictated by where you are located, crop rotation and soil types. In Indiana, check the Purdue nitrogen management guidelines. Use data and tables to locate your region of the state, identify your N price and corn grain price, and determine how much additional N is required to reach the economically optimum N fertilizer rate. Within Indiana, recommended rates vary significantly from east to west and north to south.
For this recommendation, the source of N does not matter.
Licht: When properly applied, commercial nitrogen source does not matter. Organic N sources could matter because it takes longer to convert those sources to plant-available nitrogen.
Knowing how much additional N to apply based on commodity price and N price is important. In Iowa, there is a new tool: N-FACT (see story below). Use it to help make this decision. Typically, higher N price and lower commodity prices lean toward lower N rates.
SCENARIO 2: This no-till stand averaged out at 32,000 plants per acre. How should it be managed for the rest of the season?
Use digital N tools
Both Quinn and Licht encourage using state recommendations for nitrogen rates. Often, that may be a digital tool. Here is a look at a few options:
N-FACT. The Nitrogen Fertilizer Application Consultation Tool is a calculator developed by ISU as part of the Iowa Nitrogen Initiative. It is exclusively based on Iowa trials. Besides corn and nitrogen prices, you must select how much nitrogen you believe is in the soil at the beginning of the season.
Example 1: Select Boone County, Iowa, home of the Farm Progress Show site. Start with 20 pounds of N or less. Corn price is $4.25 per bushel; N price is 40 cents per pound. Economic optimum N application rate range is 122 to 182 pounds per acre. Actual economic optimum rate is 164 pounds, producing 274.7 bushels. Highest actual yield, 275.4 bushels, comes at a projected rate of 181 pounds of N.
Example 2: Use the same parameters as Example 1, except: Corn is $4 and N is 50 cents. Rate range is 117 to 174 pounds, with economic optimum at 159 pounds for a yield of 274 bushels per acre. Agronomic optimum does not change.
Corn Nitrogen Rate Calculator. This is a regional calculator put together by land-grant universities in Illinois, Indiana, Michigan, Minnesota, Ohio and Wisconsin.
Example 1: Select Minnesota, with corn at $4.25 per bushel and N at 40 cents per pound. The “profitable N rate range” is 139 to 162 pounds per acre, with economic optimum at 150 pounds. Actual application rate would be 182 pounds of anhydrous ammonia.
Example 2: Use the same parameters as Example 3, except: Corn is $4 and N is 50 cents. The new rate range is 113 to 154 pounds, with economic optimum at 141 pounds and an actual application rate of 171 pounds.
Nebraska Corn Nitrogen Calculator. If you farm in Nebraska and want to use this tool, be prepared with detailed information about soil type, organic matter, and water properties if you irrigate.
North Dakota crop nitrogen recommendation calculators. Find calculators for North Dakota and specific regions of surrounding states. There are separate calculators for corn, barley, sunflowers and wheat.
Other states. South Dakota State University Extension offers a general fertilizer calculator. Kansas State Extension refers farmers to the Corn Nitrogen Rate Calculator and suggests using Iowa information. There is no digital N rate calculator specific to Missouri. Extension offers recommendations built around multiple factors.