Being able to calculate how much fertilizer to put on to apply the right amount of nitrogen is important. (DTN/The Progressive Farmer file photo by Jim Patrico)

Fertilizer math is fairly straightforward, but since most growers (and even agronomists) only calculate it once or twice a year (fall and spring), it is easy to forget the routine.

That math can get more confusing this season as we put together the puzzle of buying the most cost-effective fertilizer, hitting yield goals while watching expenses, and taking into account the needs of modern hybrids and varieties.

I was reminded of how confusing that math can be in an email from a reader who stated that he reads many articles about nitrogen use on corn and finds the messaging quite confusing: Farmers (and agronomists) use different terms in different regions, and compute corn's nitrogen needs quite differently depending on state recommendations and other factors. Even the way we track how many units of nitrogen are actually in a unit of fertilizer can be complicated, depending on whether the product used is a solid, liquid solution, or gas.

He wrote: "I typically put on 35 to 40 gallons of 32% split applied. One -- is this enough for 180 bu corn? Also is this 350/400 pounds of N as many articles (seem to) refer to or what is (the actual) pounds at this rate per acre. Or do I go back to units of N (per bushel). In which case at 180 bu, I would need 60 gallons of 32% for corn on corn?"

How much nitrogen to apply on corn? That is a complex question and there are many approaches. Gone is the day when we could use the old Iowa State approach of 1.2 pounds per bushel expected yield and take a credit for soybeans (1 pound per bushel soybean yield ) if in a corn/soybean rotation. That seemed to work when N was inexpensive, hybrids weren't efficient, most N was put on preplant (fall) and we didn't worry about losing nitrates into our watersheds and the Gulf of Mexico.

Today N is expensive, corn price is low, and we can't let N escape into the environment. Today's corn hybrids also are much more nitrogen efficient, and continuous corn is common. We see rates of 0.9 to 1.0 pound per bushel and some farmers are even pushing it to 0.7 to 0.8 pound per bushel yield goal. In general I believe the 1 pound per bushel expected yield works quite well, but we need to take the right credits and apply that N smartly to protect it from losses. As yields go up from 200 to 250 and now even 300 bushels per acre, it takes more N per acre and we have to be smarter on how we manage that investment.