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Phosphate budget for dairy farmers

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  2. Land and soil »
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  5. Phosphate budget for dairy 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.

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Inputs

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
100     = 

2. From soil
P released from soil
kg P/ha/yr
Add 3 kg P/ha/yr to account for the phosphate (P) released by your soil. = 

3. Effluent phosphate input
Select the figure corresponding to your production.
Milksolids/ha 600 800 1000 1200 1400 1600
Effluent P input kg/ha/yr 1 2 3 4 5 6
Effluent P
kg P/ha/yr
= 
Note: This assumes that effluent is applied to the whole farm. In reality, your effluent block will be receiving a concentrated loading of nutrients from across the farm.
  Total P Inputs
kg P/ha/yr
 

Total P inputs

 = 

Outputs

1. Milk production

 P in milk
kg P/ha/yr
Milksolids/hax 0.012

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 as milk.

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.
  Low
(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.