Whether you’re hungering for that perfect food plot or that bountiful garden, don’t forget to feed your soil. My mouth waters thinking about fresh cucumbers and tomatoes that I will be getting from our garden, and my heart pounds with the thoughts of a giant buck in my honey hole; but without proper nutrients in the soil my grand prospects would only be fulfilled at the grocery store and the Outdoor Channel. I must find a way to keep the soil fertile and to keep my fields growing great tomatoes, flavorful watermelons, and lush wildlife mixes.
There are many fertilizer options out there, liquid and solid, organic and synthetic. Typically, the organic stuff is much weaker of a concentration and much more expensive. I use the synthetic pelletized fertilizer in my deer food plots and to initially correct my garden after a long year of growth. However, pelletized fertilizer only contains the three primary macronutrients, nitrogen, phosphorus, and potassium. There are other small, but necessary nutrients such as boron, iron and zinc that must be released from other sources. I distribute composted matter and manure to disperse these life-giving nutrients.
I mentioned correcting the soil. The only way to really do that is to send a soil sample in to your local extension office. After the growing season is over, merely go to your local co-op and ask for soil sample containers. Fill with dirt, fill out the instructions, and send it in. In a couple of weeks you will have the results. It will have the recommended amount of nutrients and lime or sulfur listed. The lime and sulfur pertains for the most part to pH (but lime also adds necessary macronutrients as calcium and magnesium).
The outside of a fertilizer package contains a group of three numbers, such as 13-13-13 or 5-10-10. Each pair of numbers represents the percent of those three primary macronutrients. The first is nitrogen, the second is phosphorus, and the third is potassium. The soil sample results will have the recommend amount of nutrients to amend to the soil. To calculate the amount of fertilizer you need, divide the recommended amount with the percent fertilizer you are using and you will have the number of pounds needed for the job, by the acre. For example, the results say you need 40 lbs. nitrogen, 40 lbs. phosphorus and 40 lbs. potassium per acre. If you use 13-13-13, divide 40 by 13% to equal 308 lbs. This means that using 308 lbs. of 13-13-13 fertilizer there will be 40 lbs. of nitrogen, 40 lbs. of phosphorus, and 40 lbs. of potassium available to that acre of ground. However, you are not reduced to merely using 13-13-13. Some fertilizers may be beneficial in other ways. For example, some fertilizers may dissolve more quickly, be more light, easier to spread, or (most importantly in my opinion) cheaper. Using the same method, you will find that it only takes 235 lbs. of 17-17-17 fertilizer for the same job. If you divide the fertilizers into 50 lb. bags, that comes to 6.2 bags of 13-13-13 (308/50=6.2) and 4.7 bags of 17-17-17 (235/50=4.7). You can then multiply the price by the amount of bags to find the most economical fertilizer.
You are likely to not get such an easy number with all of the recommended nutrients in equal amounts. If the results are in different amounts, just find the proportions and calculate as before. For instance, if the results said you need 60 lbs. nitrogen, 30 lbs. phosphorus, and 60 lbs. potassium, the proportions are then 2:1:2. Find a fertilizer with the same proportions, such as 20-10-20, and calculate as before.
This hopefully helps in calculating the amount of fertilizer used in your garden or green field. Knowing the correct amount to apply not only saves you money but also results in healthier plants and a full stomach. You know the old saying; too much of anything is a bad thing!