Fertilizer grade and fertilizer ratio are used in determining the amount of fertilizer to be applied on a piece of land.The amount of fertilizer to apply per hectare depends on the amount of nutrients required and fertilizer grade available.
Take for example a piece of land that requires 120kg of N, 60 kg of P2O5 and 80 kg of K2O to be applied per hectare. Perhaps only the following fertilizers are available: sulphate of ammonium (21% N), single superphosphate (18% P2O5) and nitrate of potash (60% K2O). The following amount of each fertilizer will need to be applied per hectare on the piece of land.
(a) 100kg of the sulphate of ammonium contain
21kg of nitrogen. To get 120 kg you will require:
120kg
x 100
21
=571.42kg/ha
(b) 100kg of single superphosphate contain
18kg of P2O5. To get 60kg , you will require:
60kg x 100
18
= 333.33kg/ha
(c) 100kg of nitrate of potash contain 60kg of
K2O. to get 80k, you will require:
80kg x 100
60
=133.33 kg/ha