Skip to main content

Phosphate budget for drystock farmers

This worksheet has been developed by the Waikato Farm Environment Award Trust, with funding from the Ministry of Agriculture and Forestry (MAF) Sustainable Farming Fund. Waikato Regional Council and Dexcel also contributed to the project.

Use this image to navigate to Farm Environment Awards


1. Fertiliser

Divide the percentage of phosphate (P) in your fertiliser (the P rating) by 100 and then multiply by your rate of application.
(For example, superphosphate has about 9 percent P, while DAP and Triple super phosphate have 20 percent P.)
 %P  x kg/ha/yr   Fertiliser P input
kg P/ha/yr

2. From soil

P released from soil
kg P/ha/yr
Add 3 kg P/ha/yr to account for the phosphate released by your soil.
  Total P inputs
kg P/ha/yr

Total P inputs


1. Wool

Multiply the amount of wool sold (kg/ha) by 0.01 to give you the amount of P/ha/yr in wool.
  P in wool
kg P/ha/yr
Wool sold kg/ha x 0.01

2. Stock

Some drystock farmers will be aware of their stock units while others prefer to keep track of liveweights as a measure of stock sold off the farm. Choose the measure that best suits your situation.


Multipy the amount of stock sold (SU/ha) by 0.5 to give you the amount of P/ha/yr you lose in animals.
  P in animals
kg P/ha/yr
Stock sold SU/ha x 0.5


Multiply your liveweight sold (kg/ha) by 0.008 to give you the amount of P/ha/yr going off the farm in meat.
  P in animals
kg P/ha/yr
Total kg liveweight sold kg/ha x 0.008
  Total P outputs
kg P/ha/yr

Total P outputs

Note: Bought in feed and feed sold off the farm are additional inputs and outputs that could be included in a full nutrient budget.

Farm phosphate surplus

This gives your total farm surplus of phosphate - that is, the amount of phosphate left in your system after your product leaves the farm.

Farm P surplus/deficit

The significance of your farm phosphate surplus depends on your soil's Olsen P status. Assuming your Olsen P is at the optimum level, use the table below to get an idea of the amount of phosphate you are retaining in your soil. If your farm surplus is high, you are more likely to be losing valuable phosphate to waterways where it reduces water quality.
(could be mining your soil P reserves)
Medium High
(may be accumulating soil P unnecessarily)
Farm P Surplus Less than 20 20 to 30 Above 30

Find out about reducing the effects of phosphorus on waterways.