How is the supply of nutrients in the soil calculated?

Have you ever wondered how much soil is in your garden or block? And how is the stock of elements in it calculated?

The results you receive from the Laboratory of NIK Agro Service are in mg/kg. But what do these numbers mean and how do you calculate the stock in your soil?

To convert mg/kg of a nutrient into an actual amount (kilograms), you need to know the following parameters:

• The area for which you want to calculate the amount of nutritional elements;
• The bulk density of the soil. Volumetric density is the dry weight of the soil per unit volume. Most soils have a bulk density1.1-1.6 g/cm³(=t/m³) *;
• The depth of the layer for which you want to do the calculations.

* Volumetric densityis different not only between individual soil types, but often also between different fields with the same soil type. To find out what is the volumetric density of the soil in a particular field, it is necessary to make analyzes for volume density.

An example of calculating the supply of nutrients in the soil:

We have a block from which three soil samples were taken and the results of the analyzes are:

On average for the block we have 7.31 mg/kg total mineral nitrogen (NO₃-N + NH₄-N), 99.04 mg/kg phosphorus and 227.12 mg/kg potassium.

We will calculate the content and stock of nutrients in the layer of 0-30 cm, since it is at such a depth that the active, feeding roots of the majority of agricultural crops are located.

To do this, we must first know the weight of the soil in this layer.

1 acre = 1 000 m² (square meters)

The layer has a depth of 0.3 m/30 cm/, therefore the volume of the layer is:

1000 x 0.3 = 300 m³(cubic meters)

Once we know what the volume is, we can calculate the weight of the soil in this layer by multiplying it by the volume density:

300 m³x 1.2 t/m³= 360 t (tons)

Then we multiply these values by the amount of soil in one acre:

Nitrogen:7.31 x 360,000 = 2,193,000 mg/deca

Phosphorus:99.04 x 360,000 = 35,653,200 mg/dca

Potassium:227.12 x 360,000 = 81,763,200 mg/dca

Finally, to convert from mg/acre to kg/acre, we divide by 1,000,000 (1 kg = 1,000,000 mg).

Theoretically, the crop that you are going to grow in this area and has its active root system in the layer up to 30 cm will have 2.19 kg of nitrogen, 35.65 kg of phosphorus and81.76 kg of potassium.

For more information about soil analyses, you can contact NIK Agro Service.