If you already have enough N, P, or K to meet your yield goal in a spot in your field, why should you add more? On the other hand, if you have a few acres that are super short on any one nutrient, increasing your fertility rate in that area could really boost your yield and profit. Varying your fertilizer rate through the field is not only a wise agronomic move, but it is the most environmentally responsible way to apply crop nutrients.
All this sounds great, but what targets should you be shooting for? Below are 3 different options for you to consider, and I’ll share how we do things on our farm.
CROP REMOVAL.
We use an inexpensive software program called VRAFY to replace fertility we’ve removed last year or the last two years, depending on how often we spread fertilizer. VRAFY takes your yield map from last year (or the last two years) and simply runs calculations on nutrient removal based on yield. Then, it creates a variable-rate prescription map that easily imports into pretty much any brand of equipment. It’s simple, and this program allows you to maintain fertility levels over a period of years.
TARGET LEVELS.
This is what we use for most nutrients. Using Mehlich 3 analysis, we are shooting for these levels in many fields: 100 ppm P, 4% K, 10:1 P:Zn, 30:1 P:Cu, and 1000:1 Ca:B. We use the VRAFY software to create variable rate maps to get every area of these specific fields up to these levels. We then run the scripts in our floater or sprayer, depending on if we are applying dry or liquid fertilizer.
YIELD POTENTIAL.
While this is the most complicated method, it’s also probably the best. First, we create a “Projected Yield” map in the spring. This is based on past history, but we can tweak it if necessary. In VRAFY, it takes just a few seconds to create, and we have been impressed with the accuracy. To that, we add in our soil test data with carryover nitrogen and organic matter, since nitrogen is released in soil based on organic matter. You can add more N to the formula if you are in high carbon residue (for example, corn-on-corn) or if you are worried about loss. In our very heavy soils, we can apply quite a bit of nitrogen safely, so loss is usually minimal. On the next page is an example of a map and a script we created for one field this spring.
By looking at this chart, you can see how we will vary the applied urea rate from 196 pounds all the way up to 562 pounds!! Think of the savings in the poor areas and where organic matter is high.
Varying micronutrients is just as easy as varying rates of macronutrients. With the floater we use on our farm, we have a “micro” bin. This spring, for example, we had zinc sulfate in there, so we were applying phosphorus and urea from the big bins and zinc sulfate from the small bin, all at varying rates as we crossed the field. Best of all, the machine does all the work. The operator just drives.
If you’ve never done any of the things I listed in this article, I’m guessing you may be a little nervous to jump into something different. On our farm, we had never done any of these things prior to a few years ago, but we stepped into them slowly. Now, we’re 100% comfortable with everything I mentioned here.
Applying different rates of fertilizer as you cross the field has enormous benefits, and especially in a year like this one where everyone is trying to spend their money as wisely as possible, I can’t say enough good things about the VRAFY software we’re using and the variable rate technology in today’s equipment – IT’S AWESOME!
