Question

A fertilizer has a 20-15-5 material. What do these numbers on the label directly represent? What calculations can convert them to the actual nutrients?​

Answer 1

The number 20-15-5 reperesent the weight percent of three important ingredients N,P and K (i.e (N-P₂O₅-K₂O)) repectively.

Let us assume we have a total weight of 100 kg of fertilizer then-

Weight of Nitrogen (N) = 0.20*100 =20 kg

Weight of Phosphate (P₂O₅) = 0.15*100 =15 kg

The proportion of P in P2O5 is [62 / 142] = 0.437

Phosphourous Content= 0.437 * 15 = 6.555 kg

Weight of Potash K2O= 0.05*100 = 5 kg

The percentage of K in K2O is [78 / 94]= 0.83

Potassim Content = 0.83*5 = 4.15