Never, ever, ever run short on nitrogen.

About 15 years ago, I was talking to a farmer who said those exact words to me based on some trial work over the previous five years. He was part of a small group of farmers who would run the same trials on their farms each season just so they could learn from each other and compare notes. A few years earlier, the University of Minnesota had convinced these farmers to run nitrogen trials. The university’s belief, according to this farmer, was that farmers were using too much nitrogen. Here is how he described the results of their five years’ worth of trials.

“In a couple of the years, the university was right. We were able to cut back on nitrogen and still get the same yield. One year, we cut back N and lost a little yield, but what we lost was about what we saved in fertilizer expense, so it was a wash. The other 2 years, we cut back on N and it was terrible. We lost way more in each of those years than we ever saved on nitrogen over 5 years.”

You and I both know if you want to maximize corn yield, you can’t run short on nitrogen, not even for a single day. How do you balance that with the environmental issues with nitrogen, as well as the expense?

Chart describing cumulative nitrogen use in corn and which parts of the crop use nitrogen as development continues through the vegetative and reproductive stages. Source: Iowa State University Extension and Outreach

Here are my top 7 pieces of advice.

Understand your soil and your weather.

For example, a 5 CEC in Florida is completely different than a 25 CEC in South Dakota. In Florida, the ground never freezes, and it rains every other day (or at least that’s what it seems like every time I’m there). In South Dakota, the ground is frozen 5 months out of the year; and as I write this, in the last 10 months we’ve had a grand total of 8 inches of precipitation, including snow. In other words, in my heavy soil in South Dakota, the risk of nitrogen leaching is very small. In light soil in Florida the risk of nitrogen leaching is extremely high.

Look at cost to value.

For example, when the corn price is $5 per bushel instead of $2, yields are 230 bushels instead of 130, and the nitrogen cost for an additional 20 pounds is $8 instead of $16, your odds the additional nitrogen will pay are a lot better.

Know your crop’s needs.

Corn requires about 1.12 pounds of nitrogen per bushel. That’s a fact. Just as importantly, though, you need to know when this nitrogen is used. The chart on the upper right side of this page shows that 80% of nitrogen use is after V12, so you need ample nitrogen available late in the season, but you also don’t want to short your plants early. You also need rainfall or irrigation to move nitrogen into plants, so err on the early side rather than the late side for applications if you are in a dry area.

Know how much nitrogen your crop will get from other sources.

While total nitrogen needs are indeed 1.12 pounds per bushel, don’t forget to add in carryover nitrogen from last year and organic matter mineralization. In the Midwestern United States, we usually figure 20 to 30 pounds of nitrogen for each one point of organic matter. For example, a 5% organic matter soil will get 100 to 150 pounds released for free each year, so that’s a whole lot of N you don’t have to apply.

Be realistic about your yield goals.

If you’ve never raised 220-bushel corn and now your yield goal is 300, I don’t want to discourage you, but yield jumps of 20 and 40 bushels are a lot more common than 80-bushel yield increases in a single year.

Vary your application rates when necessary.

If you’ve got fields where there are some great areas and some terrible spots, don’t put the same rate of nitrogen across the whole field. If you do, you are likely to see the excess nitrogen leach out of the bad spots, stripping away calcium and lowering soil pH. We’ve seen good soils drop their pH levels into the 4’s due to continued over-application of nitrogen.

Pull a few pre-sidedress nitrate tests.

When we first started doing this a few years ago, I was all ready to have our guys apply 100 pounds of extra nitrogen per acre on a few fields. As it turned out, we didn’t need any of that nitrogen on some of our land. Every once in a while, there is a crazy amount of nitrogen out in your soil, and there’s no point in adding more when you already have enough to exceed your yield goal.