By Darren Hefty

With fertilizer prices at lofty levels once again going into 2012, a fair question to ask yourself is “Am I applying too much fertilizer?”  With crop prices also at decent levels, you also need to consider, “Am I applying ENOUGH fertilizer?”

Let’s face it.  Proper nutrition for crops and weed control are the two biggest yield-limiting factors in most crops.  You have lots of tools for killing weeds, and the best part is you get to see what weeds pop up, and you know for sure if you used enough herbicide to take them out.  With fertility, the problems and the successes are often not visually obvious.  Here’s a plan for evaluating and adjusting your crop nutrition program for this coming season.

  1. If your fertilizer plan starts with, “Let’s do the same thing we did last year,” it is probably costing you money in either loss of yield or improper balance of nutrients.
  2. You must start with a soil test to see where you’re at not only in each field but in different areas of the field where soil type or topography change.  It only costs about $30 to pull a soil sample yourself (with a shovel or an inexpensive soil probe) and have a complete analysis run.  If you’ve never done soil testing, at least start with one or two fields this year.
  3. Consider what the crop you’re planning to plant will remove from the soil.  For example, to produce the grain and stover of a 100 bushel wheat crop, your crop needs approximately:
    • 198 pounds of Nitrogen
    • 68 pounds of Phosphate
    • 135 pounds of K2O Potassium
    • 24 pounds of Calcium
    • 22 pounds of Sulfur
    • Several different micronutrients and other essential plant nutrients
    • If you raise 150 bushels, take each of those numbers times 1.5.  If you raise 50 bushel wheat, take each number times 0.5 to determine how much your crop will use.
      Keep in mind that even if you leave all the stover (residue) in the field after harvest, lots of fertility leaves the field in your grain.  At a minimum, I’d suggest at least replacing that.
  4. You don’t have to soil test every single year.  If you raised 100 bushel wheat and fertilized for 80 bushels last year, you know you need to apply more fertilizer this year to make up for what you robbed from the soil.  By the same measure, if you only raised 40 bushels, you may have some carryover P and K to feed this year’s crop.
  5. Use plant tissue analysis as a report card for your fertility program.  Take one field this year and pick a good area of the field and a not so good area.  GPS mark those areas or put a tall flag in each spot so you can pull plant tissue tests each week for 2 or 3 months this growing season.  It costs about $20 per sample for the analysis.  The money you invest here should pay you back many times over when you’re adjusting your fertilizer plans for next year’s crop.

When we started doing this on our farm, we learned we were wasting money by applying too much nitrogen trying to fix poor-yielding areas.  Instead, we took some of the money we planned to spend on nitrogen and shifted it to the potassium and micronutrients our plant tissue tests showed us our crops needed.  When we did that, our yields went up with the very next crop.  If you’d like to learn more about determining the right amount of nutrition to maximize your yields, please attend one of our Ag PhD Winter Workshops over the next few months.