The Q&A Archives: Fertilizer Formula

Question: In one of your Q&A you have a formula for figuring out the amount of fertilzer to place on a 20,000 Sq lawn, the soil test recommends 3lbs
Of N per every 1000 square feet in a divided spring and fall application. The formular then goes on to say that to determine the amount of square feet at 1lb per square feet that a fertilizer bag will cover. multiply the weight of the bag my the percentage nitrogen on the label, then multiply by 1000.The numbers on the bag are N30 P1 k1, and it is a 40lb bag. So If
we do this we get 12000 sq ft. and it goes on to
say but we want 3lbs of N per 1000sqft, one sack
will cover 4,000 sq ft, and our home owner will buy 5 sacks of fertiliizer 20,000sqft/4000sqft
The part I don't understand is where did you come up with the 4,000 sq ft, did you divide 12,000 sq ft by 3, and then divide 4,000 by 20,000 to come up with 5 or what. thanks ahead of time for your response.

Answer: I think you've got it! A bag could cover 12000 sqft at a pound rate, but we need a three pound rate. So we divide the square footage per bag by three. That gives us the 4000 sqft per bag. Using 4000 per bag, and knowing we have 20000 to cover, we divide 20 000 by 4000 to get five -- the number of bags we need.

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