There’s a lot of money tied up in a field before you ever pull into it with a planter.
Some of it went on last fall. Some came out of a manure spreader a few years back. Some is still sitting in the stalks left after harvest.
When it’s time to put together next year’s fertilizer program, it’s easy to start with what we’re going to buy. But it’s worth taking a little time to look at what’s already there.
Before placing the next fertilizer order, look at what went on, what came off, and which nutrient contributions are already figured into the plan.
Start With What You Know About the Field
Most growers can tell you things about a field that will never show up on a soil test.
That quarter has had manure for years. That farm had stalks baled off. That piece caught a rain when everything else burned up and hauled out a much bigger crop.
Those details matter when you sit down to figure out fertility.
Pull out the soil tests, application records, and yield history together. See whether the recommendation in front of you makes sense with what has actually happened on those acres.
A program that fit five years ago may need another look today. Especially if the yields, rotation, or manure applications have changed.
That Manure Application Brought More Than Nitrogen
If you’ve spread manure, you’ve already made a fertility investment.
The nitrogen usually gets plenty of attention. But phosphorus and potassium came along with it, and those nutrients need to be counted too.
Manure varies. What’s in a load depends on the livestock, bedding, storage, and how it was handled. A manure analysis and a good application record give you something solid to work from. Repeated applications can also build soil phosphorus, especially when rates are based on the crop’s nitrogen needs. University of Minnesota Extension explains how to account for manure phosphorus.
Before you order fertilizer for those acres, make sure those contributions made it into the recommendation.
It’s an easy thing to overlook when the spreading happened months ago and the fertilizer order is sitting in front of you now.
What Went Out the Gate?
We pay close attention to the bushels leaving a field. It’s worth paying attention to what else left with them.
If you baled stalks or chopped silage, you hauled nutrients away along with that material. That changes what’s left for the next crop.
If the residue stayed, those nutrients stayed on the farm and can cycle back into the soil. The amount and timing of that contribution still matter. Nutrients sitting in residue aren’t all available to the next crop at once. Iowa State University Extension covers how residue removal affects nutrient cycling.
Think about two neighboring fields. Same crop. Similar yield. One had stalks baled, and the other didn’t.
That’s a difference worth bringing up when you review the fertility plan.
Make Sure You Aren’t Counting the Same Nutrients Twice
This part takes a little care.
Some contributions may already be figured into your recommendation. Your soil-test recommendation accounts for the soil’s nutrient supply according to the method being used. A nitrogen recommendation may already include an adjustment for the previous crop.
You need to know what’s included before subtracting anything else.
Sit down with whoever helps build your program and walk through the numbers. Have them show you where the manure credits went and how the previous crop was handled.
There’s nothing wrong with asking how a recommendation was built. You’re the one paying for it, and you’re the one raising the crop.
Start With One Farm
You don’t have to sort through every acre in one afternoon.
Pick a field where you have decent records. Lay out:
- Recent soil tests and the recommendations that came with them.
- Fertilizer and manure application records.
- Actual harvested yields.
- Previous crops and any stalks or other residue hauled off.
- Nutrient credits already included in next season’s plan.
Then work through it.
Maybe the review supports the program you already had in mind. Maybe there’s a manure contribution that never got counted. Maybe you find out the records aren’t good enough to justify a change yet.
Any of those answers gives you a better place to start.
The title says you already own more nutrients than you think. How much more will depend on the field. Some of those nutrients may help feed the next crop. Some may take longer to become available, and some fields will still need a substantial fertilizer investment.
