Over 90% of food plotters are improperly fertilizing their food plots. Where does that number come from? I receive thousands of soil samples each year from new clients and over 90% of them come in imbalanced on p or k or both major nutrients. There is a reason for this. Most food plotters receive generic recommendations. With most food plotters planting mixes, the soil testing labs are not recommending for that specific mix.
To properly fertilize one's food plot you need to know these things. What is your yield goal in tons per acre. Note this would be on a dry matter basis. For example if your perennial clover mix produced 10 ton of wet forage per that season at an average moisture content of 80%, that would be 4000 lbs of dry matter. (20,000 lbs total weight x .20 % dry = 4000 lbs dry matter). Why do we talk dry matter? Because forages can vary in overall plant moisture.
Once we have an expected yield goal, we need to know what the average nutrient content of the mix your planting. How many of you know that? Don't feel bad, next to no one does in the wildlife industry, but they should. Here is an example analysis.
4000 lbs dry matter for mass builder perennial mix
calcium % 1.40
phosphorous % 0.30
magnesium % 0.30
potassium % 2.50
sulfur % 0.25
to determine how much potassium is removed during the current season by mass builder perennial mix the calculation is this. 4000 lbs x .0250 = 100 lbs potassium mined from the soil.
to determine how much phosphorous is removed the calculation is 4000 x .003 = 12 lbs phosphorous mined from the soil.
Now how would one replace those nutrients removed from the soil? If the fertilizer supplier handled a 0-20-20 fertilizer and a 0-0-60 fertilizer you would use this combination.
12 lbs phosphorous / .20 (density of phosphorous in 0-20-20) = 60 lbs of 0-20-20 needed to provide enough phosphorous to meet what was removed.
You had 100 lbs of potassium mined from the soil. If you added 60 lbs of 0-20-20 you just added 12 lbs of potassium from there. We are now needed 100 lbs- 12 lbs = 88 more pounds of potassium. We now will get the rest of what we need by using 0-0-60. The calculation for that would be 88 pounds / .60 (percent potassium in 0-0-60) = 146 lbs of 0-0-60 to replace what was removed from the soil.
The last part of the equation would be if you were deficient or excess in either phosphorous or potassium. If deficient, then you need to add some extra of those nutrients to try to regain nutrient balance. If your excess in one or both of those nutrients, then we wouldn't need to add any or as much of those nutrients in the current growing season.
One other thing to consider. If forages are produced but not consumed by deer, they are not nutrients removed from the soil. Once those plants are broken back down into the soil, those nutrients are still there. There are various ways to measure yield and removal. You can use exclusion cages and also squares. We will cover this in a future blog.
So my challenge to not just you as individuals is to ask your wildlife seed provider for real data to help you best fertilize properly or take your own forage tissue samples and measure your yields to help better fertilize. Hope this helps you all. Be well.