There are two lines of thought. One is based on surface area and bulk density and mass per ah to some depth. The other is to simply dose to a particular concentration. If one has the data these are interconvertible

Some of the assumption-

depth of soil sampling (I assumed 0.3 m). If you collected soil at a depth of 0.17 m, the influence of fertilizer applied by top-dressing on the result is greater than if you sample at 0.3 m depth

Kg Soil per hectare

Kgsoil/.ha = bulk density (g/cm^3 )* soil depth( cm) *1Kg/1000g * 10^8 cm^2/ha

Kg soil/ha = 22.4 *10^5 Kg

Only if

Bulk Density = 1.32 g/cm3

Soil Depth = 17 cm

0.07% = 0.7g/Kg

And for 5 kg=0.7*5 g/kg=3.5 g/kg.

Therefore 0.7g/Kg * 22.4 [10^5] = 15.68 * 10^5 g/ha

15.68 [10^5]kg/ha * kg/1000g = 1568Kg TN per ha

Hello Phurpa,

good question and a calculation for it see here:

I calculated the 75 kg N per hectare on kg soil per hectare for the topsoil.

For this, the following assumptions:

Soil density: 1.4 t/m3

Topsoil depth: 0.3 m

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The following calculation to determine the topsoil mass for 1 hectare:

Calculate topsoil volume

topsoil depth x area = topsoil volume

Calculation

0,3m x 10 000 m2 = 3000 m3

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Calculate Topsoil mass

Topsoil volume x soil density

Calculation

3000 m3 x 1,4 t/m3 = 4200 t / 4 200 000 kg

75 kg N / ha is applied, i.e. 75 kg N per 4 200 000 kg soil or 75 000 g N per 4 200 000 kg soil.

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How many g of N on 1 kg of soil for a fertilization of 75 kg N / ha?

Calculation

75000 divided by 4 200 000 kg topsoil mass = 0.017857143 g N / kg topsoil

75 kg N / hectare is equal to 0.017857143 g N / kg topsoil.

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You want to know how many N in grams you should fertilize on 5 kg of soil?

0.017857143 g N / kg topsoil x 5 kg topsoil = 0.089285714 g

It is 0.089285714 g so about 0.089 g.

Best regards from Osnabrueck, Stefan