Never, ever, ever run short on nitrogen.
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 since nitrogen prices have reached an all-time high? Here are my top 7 pieces of advice.
1) Understand your soil and your weather. For example, a 5 CEC in Florida is whole 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 8.5 months we’ve had a grand total of 8 inches of precipitation, including the 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.
2) Look at the cost to value. For example, when the corn price is $8 per bushel instead of $3 and yields are 240 bushels instead of 140, your odds are a lot better the additional nitrogen will pay. On the other hand, this year’s price of $1+ per unit of N is not good, especially since we were buying it for one-third the price just 18 months ago.
3) Know your crop’s needs. Corn requires 1.12 pounds of nitrogen per bushel. That’s a fact. Just as importantly, though, you need to know when this nitrogen is used. Roughly 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 on. 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.
4) 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 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. Since we’ve had a drought for almost 2 years in our area, we saw record nitrogen carried over from the last growing season. If you haven’t soil tested, you may not realize that nitrogen is there, meaning you would be likely to overapply and overspend this spring.
5) Be realistic about your yield goals. If you’ve never raised 250-bushel corn before and now your yield goal is 300, I don’t want to discourage you, but yield jumps of 20 or 30 bushels are a lot more common than 50-bushel yield increases in one year.
6) 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 into the 4’s for pH due to continued over-application of nitrogen.
7) Just last year I was all ready to have our guys throw 100 pounds of extra nitrogen per acre on a few fields. As it turned out, we didn’t need any of it. Before you apply any more nitrogen to any crop this season, be sure to pull a few soil tests! It only costs $5 to run a nitrate test, but it could save you thousands in expense or it could really boost your yields if you actually need more nitrogen. Testing is the only way to be sure you have enough N to hit your yield goals. With corn prices and fertilizer costs at or near all-time highs, there has never been a more important time to soil test. When you pull soil cores mid-season, our suggestion is to go all the way down to 24 inches deep. Chances are you have roots at that depth already, and your crop can use up the N from anywhere in that range pretty well before it’s lost in most cases.