There are recommended application rates for each fertiliser and each crop. This rate is stated in kilograms per hectare (Kg/ha). When the rate and the area of your plot of land are known, it can be calculated how much fertiliser to put on. The recommended application rate for potatoes is as follows to obtain a yield of 30 tons per hectare:
- 135 kg of N per hectare.
- 132 kg of P per hectare.
- 200 kg of K per hectare.
- The land area is 5 meters in width and 10 meters in length = 10 x 5 = 50 m2.
- Less fertiliser is required than 135 kg. It is because 1 hectare is (100 m x 100 m = 10 000 m2).
- The area of the garden plot is only 50 m2.
- The fertiliser must be applied at the correct rate as an excess may cause more harm than good to your cropping system.
The following calculations should be conducted:
Given: The plot size = 50 m2
Potatoes need: N = 135 kg per 10 000 m2, P = 132 kg per 10 000 m2, K = 200 kg per 10 000 m2
The formula is as follows:
Application rate/ 10 000 m2 x plot size
Thus, for the calculation of N
135/10 000 m2 x 50 = 0.675 kg N for plot size of 50 m2.
For the calculation of P
132/10 000 m2 x 50 = 0.66 kg P for plot size of 50 m2.
For the calculation of K
200/10 000 m2 x 50 = 1 kg K for plot size of 50 m2.
Express your answers in the ratio of NPK as follows:
|
N 0.675kg |
P 0.66kg |
K 1kg |
Divide now the biggest total by the smallest as follows:
0.675/0.66 = 1.02 rounded off to 1
0.66/0.66 = 1.00 rounded off to 1
1.00/0.66 = 1.5 rounded off to 2
The ratio is now as follows:
|
N |
P |
K |
|
1 |
1 |
2 |