So you sent off your representative soil sample(s) to Virginia Tech and have received your results.
My test results for the high tunnel told me I needed to add all of the major nutrients-N, P, and K as well as lime.
N is nitrogen which primarily promotes healthy leaves. P is phosphorus for good roots, and K is potassium for healthy fruit. If you are wondering WHY they use K: the chemical symbol K comes from kalium, the Medieval Latin for potash, which may have derived from the arabic word qali, meaning alkali.
My test recommended 90 pounds (#) per acre of N, and 75# of P and 150# K. I use Harmony fertilizer with an analysis of 5-4-3. That means it contains 5% nitrogen, 4% phosphorus and 3% potassium. Or to put it another way, each pound of Harmony contains .05# N, .04# P and .03# K. I solved for Nitrogen first. So 90 goes in the 1st box and 5 goes in the 2nd box and I put in my bed dimensions of 3 X 55 feet. After clicking the “show result button”, it showed I need to add 6.82 # of Harmony per bed or .66 oz per square foot or 41.32# per 1,000 square foot or 1800# per acre to get the N required.
You can find the Calculator here.
Now I need to figure out how much P and K 6.82 # of Harmony will supply. The formula is rate per acre X 100 divided by % nutrient per pound = pounds of fertilizer per acre. In our case we don’t know the rate per acre but we know the other numbers. % nutrient is 4 for P and 3 for K and pounds of fertilizer per acre is 1800. Here’s the equation: ? x 100/ 4 =1800 lbs per acre. To solve the equation for P, multiply 4 X 1800 and divide by 100. The result is 72# P, I needed 75#, close enough.
To solve for K multiply 3 X 1800/100=54. The soil test called for 150# per acre. Next, subtract 54 from 150, leaving 96# K per acre I need to still add. Back to calculator, I put 96 in the pounds per acre box. I have potassium sulfate which is 0-0-50. So I put 50 in the % nutrient box, keep my bed measurements and the result is .41# of additional potassium sulfate per bed in addition to the 6.82 lbs per bed of Harmony.