There are a lot of different fertilizer recommendations out there, and they are often dependent on regional soil composition and soil test results. The purpose of this thread is to explain how you take these recommendations and figure them into how much to actually apply.

I will be taking recommendations from Virginia Tech's 2019 report for flue cured tobacco. FYI, the nitrogen rates recommended for burley are significantly higher.

Their recommendations are as follows:

Nitrogen 50-80lbs/acre depending on soil depth

Phosphorous 40-230lbs/acre depending on soil test

Potassium 100-175lbs/acre depending on soil test

We will go with 80, 80, & 175 (respectively) for all of these example calculations.

This is represented as 80-80-175 lbs/acre

"but my garden is not that big!"

Yes. So let's switch to a combination of metric and imperial. This is how it makes sense to me: 1lb/acre = 1.04grams per 100 square feet.

This means that our recommendation for lbs per acre is basically the same as our recommendation for grams per 100square feet. So for every 100square feet of garden, you need 80g N, 80g P, & 175g K.

Calculations:

Let's say you have a pure N fertilizer, something like 60-0-0.

Only 60% of the weight of the fertilizer is N. Therefore if you need 80g of N, it makes sense that you would need more than 80g of the fertilizer.

The calculation is 80/0.60 = 133g.

So 133g of the 60-0-0 will give you 80g N and you will apply that amount to every 100square feet of your garden.

Let's say you have a fertilizer which is not purely one chemical.

Let's say it's 20-20-40.

So let's calculate how much fertilizer is required to get the amount of N we need.

80/0.20 = 400g per 100square feet

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