Choosing Nitrogen Rates

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The growing season has started and most corn farmers have already applied nitrogen. It is a very expensive plant food and getting the rate right may mean using a little less.

Here’s how the University of Illinois nitrogen recommendation used to work. It was formula equal to roughly one-point-two times the expected yield minus the nitrogen leftover from the previous crop. That “yield-goal-based system” recommends too much for today’s corn hybrids says University of Illinois Extension Agronomist Emerson Nafziger, “That yield-goal-based system flat-out doesn’t work anymore. The reason it doesn’t is that our yields have gone up a lot, and we are clearly showing that yields have gone up more than requirements for nitrogen have gone up.”

Nafziger believes there are two reasons for the change. First, he says the system always recommended more nitrogen than was really needed. The other is that hybrids have become much better at extracting what’s there; water and the nutrients that come with water. Nitrogen is the main one of those. Nafziger says, “Today we get higher yields and do not have to use the 1.2 pounds of nitrogen per bushel or what ever formulation people were using.”

ILLINOIS abandon the formula about ten years ago in a favor of a system used and promoted by Land Grant’s throughout the corn belt. It is called the N Rate Calculator and it actually brought the Illinois rates down by a few pounds for this year.

Nafziger says at current corn and nitrogen prices, guideline rates for corn following soybean are 154, 172, and 179 pounds of nitrogen per acre in northern, central, and southern Illinois, respectively. 200, 200, and 189 for corn after corn. Southern Illinois farmers will make note that their rate for corn after soybeans is higher than in either central or northern Illinois and lower than both of those for corn after corn.