Nutrient calculation

Use this article to learn how to calculate the amount of nutrient applied from the declared analyses and treatment rates.

The fertiliser declarations are always expressed as % weight by weight, with nutrients being declared in the oxide form in the UK.

Therefore, a 14–5–10 fertiliser contains:

• 14% w/w N
• 5% w/w P2O5
• 10% w/w K2O

Granular fertilisers

For calculating nutrient inputs for granular fertilisers, use the following formula:

Application rate (kg/ha) x (% nutrient/100) = kg nutrient/ha

• Example: 14–0–0 @ 35g/m²
• Convert application rate from g/m² to kg/ha (i.e. 35g/m² x10 = 350 kg/ha)
• Multiply product rate (kg/ha) by % N content (i.e. 14% N = 0.14) = kg N per ha (i.e. 350 x 0.14 = 49kg N/ha)

Liquid fertilisers

In order to calculate the nutrient inputs from Greenmaster Liquid fertilisers, you need to use the Specific Gravity (kg/L) of the particular product being used. This information can be found on the relevant product page.

Specific Gravity (SG) of:

• NK 1.23
• High N 1.31
• Spring & Summer 1.18
• High K 1.18
• STEP Liquid 1.15
• Effect Iron Fe 1.25
• Vitalnova Blade 1.36

For calculating nutrient inputs for liquid fertilisers, use the following formula:

Application rate (L/ha) x Specific Gravity (SG) x (% nutrient/100) = kg nutrient/ha

• Example: 12–4–6 @ 60 L/ha (SG = 1.18 kg/L)
• Convert application rate from L/ha to kg/ha (i.e. 60 L/ha 1.18 = 70.8 kg/ha)
• Multiply product rate (kg/ha) by % N content (i.e. 12% N = 0.12) = kg N per ha (i.e. 70.8 x 0.12 = 8.5kg N/ha)