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Do you have enough?

I recently discussed how we can use fertilizer ratios to simplify how much fertilizer we apply to help us keep above the MLSN guidelines. When we get a soil test done it is a static amount of nutrients found in the soil. Even if you are above the MLSN guidelines at the time of testing, it doesn't guarantee that you will remain at or above the guidelines as the grass grows and consumes nutrients.

There is math that you can use to determine exactly how much nutrient you need to apply to ensure that you remain at or above the MLSN guidelines. For many, this is much too complicated. For that reason I made a quick cheat sheet to help you determine how much of each nutrient you can expect to use each year based off a few different annual nitrogen rates.

Nutrient use is based primarily on nitrogen use so the left 2 columns are a few different nitrogen rates. The columns for each nutrient are in PPM and are designed to help you look at your current soil test PPM (mehlich 3) and determine if you have enough of that nutrient to get through the season without supplemental fertilizer applications of that nutrient.

Combine the nutrient usage with you soil tests and then pick a nutrient ratio in the fertilizer you apply to either lower your soil ppm and use what is already contained in your soils, keep the soil ppm the same, or increase the soil ppm. Even if you aren't a math wizard you can probably do this math without the use of a calculator. Sweet.

Let's say you put down 10 g N / m^2 per year. You can expect to use 34 ppm of potassium. You currently have 40 ppm on your soil test and the MLSN is 37ppm. 40 - 34 is 6 so you will go below the guidelines if you don't apply fertilizer. Cool. A 2:1 N:K ratio is probably enough to get you by. If you are worried about being so close to the MLSN put down something slightly higher like a 3:2 ratio. Not hard.

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