Fertilizer recommendations are made in elemental or oxidized form of nutrients, but not as
fertilizers themselves since different fertilizers are available with the same nutrient but with
different contents. Based on the nutrient content of a particular fertilizer, the amount of material to be applied has to be calculated.
Problem:
Let, the recommended fertilizer dose for lowland rice be 120, 60, 40 kg N, P2O5 and K2O per hectare, respectively.
The amount of fertilizer required in the form of urea,
superphosphate and muriate of potash is calculated as shown below:
To supply 46 kg N/ha, 100 kg urea is necessary (Urea contains 46% N)
To supply 120 kg N/ha 100/46 x 120 = 260.9 kg or 261 kg urea is required.
Similarly:
To supply 60 kg P2O5 = 100/16 x 60 = 375 kg of superphosphate is required (Superphosphate contains 16% P2O5).
The amount of muriate of potash required to supply 40 kg K2O per hectare is 100/58 x 40
= 68.9 kg/ha or 69 kg/ha (Muriate of potash contains 58% K2O)
Therefore,
The amount of fertilizer to be applied = [100/(Nutrient content)] * [recommended dose].
