fertilizer Fertilizer math

[dragon49]

If I give half a dose of 10-10-10, is it equivalent to a full dose of 5-5-5, and would a double dose of 10-10-10 be equivalent to a normal dose of 20-20-20?

 

[queequeg152]

correct me if im wrong.... but 10-10-10 is just a ratio of molar weights of nitrogen phos and potassium, 5-5-5, 10-10-10, and 20-20-20 are the same ratio wise.

are you looking to half the concentration of the fertilizer? if so, with respect to what?

 

[Capsicum]

Yup very right. It is just a ratio 10;10;10

PPM is what you should look at.

 

[dragon49]

K - ty 4 replies

 

[Proud Marine Dad]

correct me if im wrong.... but 10-10-10 is just a ratio of molar weights of nitrogen phos and potassium, 5-5-5, 10-10-10, and 20-20-20 are the same ratio wise.

are you looking to half the concentration of the fertilizer? if so, with respect to what?

They are percentages so 10-10-10 is 10% of each nutrient by volume so 20-20-20 would have twice the amount of N-P-K than the 10-10-10 would by weight right?

 

[Avon Barksdale]

Not quite because the P number listed is for P2O5, and the K is for K2O. So you have to multiply the P number by the mass fraction .436 (since P205 is 43.6% P by mass) and the K number by the mass fraction .83 (K2O is 83% K by mass) to get the actual percentage of phosphorus and potassium.

So a 10-10-10 fertilizer would have 10% nitrogen, 4.36% phosphorus and 8.30% potassium. But yeah the 20-20-20 would have twice as much of each for the same weight.