By Darren Hefty
1. How Much Nitrogen Does My Crop Need?
All the research on nitrogen in corn has shown that you don’t want to run short. You hopefully know how much N was in the soil to begin with and how much you’ve applied so far. Plus, you will be getting (depending on where you live and the type of growing season you’re having) 20 to 30 pounds of nitrogen for free through mineralization of each 1 percent of your soil’s organic matter.
For example: Last fall’s soil test showed 30 pounds of N left over after your soybean crop. This spring, you applied 100 pounds of nitrogen at planting time. Your soil’s organic matter percentage is 4 percent. 4 percent O.M. X 20 pounds of nitrogen release (to use the lower end of the scale) = 80 pounds. Adding 30 + 100 + 80 gives you 210 pounds of nitrogen potentially available for your crop. However, some of your nitrogen may have been lost to volatilization, leaching, or denitrification, so keep that in mind.
In the end, this comes down to an educated judgment call. Just don’t forget about the organic matter and the free release of nitrogen through mineralization. If you haven’t calculated that in, you may be overapplying your N.
2. What Other Nutrients Should I Apply?
Certainly in the case of leaching due to heavy rains, you should consider adding more sulfur and boron. However, here’s where your plant tissue program can come into play. We’ve talked about this extensively on Ag PhD Radio and in past newsletters (see www.agphd.com for more) about how we take fields on our farm and pull plant tissue samples weekly in a good area of each field and a poor area and compare the nutrient analysis to help determine what can be done to increase yields and profitability. If you’re seeing a trend appearing on multiple plant tissue tests, such as a shortage of potassium, zinc, and manganese, you can address that as well at this time.
3. How Should I Apply My Fertilizer?
We greatly prefer to see the nutrients injected into the soil. This way, the nutrients are safe from volatilization and that much closer to getting into the plants. We like to use the Hagie Nitrogen Toolbar with coulters to apply nutrients in-crop. However, if a rain is imminent, using drag hoses or Y-Drops to apply liquid fertilizer on top of the soil works adequately. We do not like broadcast applications of high rates of liquid fertilizer over the top of foliage because it can lead to extensive leaf burn. Dry fertilizer can be broadcast when the plants have no dew on the leaves, but you do run the risk of harmful accumulations in the whorl. Dry applications also will need more moisture to break the fertilizer down and get it moved into the root system.
4. What Is the Optimal Timing for Nutrient Application?
Corn needs a huge chunk of its nitrogen in the V8 to Tasseling stage. If you’ve had loss or didn’t get much nitrogen on early this season, you’ll want to get it applied by V5-V6 to make sure you don’t run short when your crop reaches the high demand stages. Otherwise, timing a sidedress around V7 is good in high rainfall or irrigated situations. In dry country, like where we farm, we like to go earlier than that because we may have to wait a while for rain. Without moisture to move the fertility into the roots, a sidedress application won’t provide much benefit.
5. Should I Use a Stabilizer With My Nitrogen?
Finally, we’re always asked about nitrogen stabilizers whenever the topic of nitrogen comes up. The answer is yes, we do see a benefit protecting the nitrogen from loss. Using a stabilizer also holds the nitrogen in the ammonium form longer, which is what your corn crop prefers.
Keep these things in mind as you make sidedress decisions on your farm this season.