Calculations for the use of fertilizer solutions

Definitions

Below we present some examples to show how fertilizer dosage is calculated whenever recommendations are available.

Recommendations are published in the following form:

All recommendations should be carefully studied and evaluated. Since some recommendations are in terms of pure P and K instead of the oxides.

Calculation of fertilizer dosage

Example for field crops fertilization

The following fertilization recommendation has been given a farmer growing a drip- irrigated squash crop:

Basic dressing (as pre-transplant application) of 60 Kg N, 120 Kg P2O5 and 70 Kg K2O per hectare.

Top dressing during the 10 mid-season weeks 210 Kg of N, 70 Kg of P2O5 and 210 Kg of K2O should be fertigated per hectare.

Calculating the pre-plant application

The recommended rates are 60 – N; 120 – P2O5 and 70 – K2O, given ratio of 1:2:1.2.

For this recommendation “Gatit 14-28-18+TE” fertilizer is the best approximation to the above recommendation. The following amount of “Gatit 14-28-18+TE” is required:

This quantity supplies the required amounts of N, P2O5 and K2O.

Calculating the mid-season application

The recommended rates are 210 – N, 70 – P2O5 , 210 – K2O , given ratio of 3:1:3 “Gatit 21-7-21+TE” fertilizer fits the recommendation.

The required amount of fertilizer is:

A total amount of 1000 kg of fertilizer should be applied during a period of ten weeks. Therefore, every week:

should be applied

A second alternative is to inject the fertilizer solution at constant concentration into the irrigation water (proportional fertigation)

If during that 10 week period, a total of 3000 m³ water/ha are to be applied, then the following “proportional” dosage should be maintained:

Example for greenhouse fertigation

The following recommendation has been given to a grower of greenhouse carnations: Nitrogen (N): 120 ppm; Phosphorus (P2O5): 60 ppm; Potassium (K2O): 240 ppm. The relationship between the three nutrients is: 2:1:4.
Gat fertilizers “Shafir4-2-8” has the adequate ratio of nutrients.

The following calculations are performed:
To reach a concentration of 1 ppm N, 1 gram N should be added to each cubic meter of irrigation water, (1 gr N per 1,000,000 gr water = 1 gr N /m³). Therefore, in order to reach 120 ppm, 120 gr N (0.12 Kg N) should be added to each m³ of irrigation water.
The required weight of “Shafir4-2-8” is calculated as follows:

The volume weight of “Shafir4-2-8” is 1.17 gr/cm³ (=1.17 Kg per Lt)

Therefore, the volume of fertilizer solution to be injected into the irrigation water is: