To convert between “parts per million” (ppm) and “kilograms per hectare” (kg/ha) requires values for the soil bulk density (in kg/m3) and the depth of the soil layer sampled (in metres).
You may choose to use a different values for bulk density like between 900-1500 kg/m3 to convert your values and an average depth of 10cm or 15cm to match your soil test results and treatment depths.
Example 1:
Converting ppm to kg/ha
If sample depth was 0.15 m (15 cm or 6 inches), then Value in kg/ha = Value in ppm x 1.5
Rationale: Value in kg/ha = Value in ppm x (1 kg/106 mg) x (1000 kg/m3, bulk density) x (0.15 m x 104 m2/ha)
Example 2 :
One hectare or 10,000 m2 x 0.1 m soil depth x 1.5 g/cm3 bulk density = 1,500 t/ha of soil.
20 × 1,500,000 kg = 30,000,000 mg-N/ha = 30 kg-N/ha
Average soil bulk densities for mineral soils are as follows:
– Well structured high organic loam soil 900 kg/m3
– Silt loam 1100 kg/m3
– Medium to fine texture loam 1300 kg/m3
– Sand 1500 kg/m3
– Compacted soil or clay subsoil 1300-1600 kg/m3
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