Best management practices for phosphorus (P) fertiliser use

Activity

Best management practices

Choice of fertiliser

• Soluble phosphate fertiliser is used where:
  
  • rapid plant response is required
  • soil P levels are required to be increased rapidly
  • plants are actively growing
  • there is a low risk of runoff
• Slow release phosphate fertiliser is used when:
  
  • there is a high risk of runoff and/or
  • a rapid plant response is not required and/or
  • soil P levels are adequate and/or
  • soil pH is less than 6.0 and annual rainfall is greater than 800mm

Rate of fertiliser application

• Nutrient application rates are determined using some or all of the following factors:
  
  • soil and plant tissue analysis
  • nutrient budgets (including any effluent and/or feed imported to the block)
  • crop type, yield/quality/stocking rate targets
  • the need for capital or maintenance applications
  • previous crop and fertiliser history
  • soil moisture conditions and expected future weather patterns
  • local knowledge
• The amount of phosphate applied per application is limited:
  
  • when high rainfall is anticipated or irrigation is planned
  • on very sandy soils, particularly for soluble phosphate fertilisers
  • when slope is greater than 25º, and/or pasture is less than 25mm high (approx. 1000 kg DM/ha)
  • during winter
• Soluble phosphate fertiliser must be applied in split dressings if the single application rate would exceed 100 kg P/ha.
  Phosphate is applied in proportion to other nutrients, according to plant requirements. (Adding excessive P when other elements limit crop or pasture growth is inefficient and could lead to P losses.)

Application technique

• Application equipment used is suitable for the conditions and fertiliser type.
  Only Spreadmark accredited spreading companies (experienced operators and calibrated equipment) should be used
• GPS and GIS technology is used for precise application and for a digital record of fertiliser application locations.
• Non-target application of fertiliser is avoided by:
• using fertiliser with larger particle sizes and few or no fine particles (aerial application)
• application techniques that direct or specifically place the fertiliser appropriately
• application in bands when sowing crops or pasture seed
• applying fertiliser only when any wind is blowing away from sensitive areas
• apply fertiliser only under agreed conditions (e.g. wind speed of less than 15 km/h)

Frequency of application

• Nutrient availability is matched to plant demand, particularly for soluble P products and liquids.
  
• Split applications are used where the single application rate would exceed 100 kg P/ha for soluble P or liquid fertiliser.
  

Timing of application

• Pasture is at least 25mm high (approx. 1000 kg DM/ha) before P is applied.
• Phosphate fertiliser is not applied after a dry (drought) period until sufficient regrowth has occurred after rain.
  
• P fertiliser is not applied when the soil is saturated
  

Fertiliser use and management measures

• P fertiliser is not applied to severely compacted soils. Soil aeration techniques are used on such soils before fertiliser application.
• To avoid fluoride toxicity to stock, pastures top-dressed with P fertiliser are not grazed for 21 days or until 25mm of rain has fallen.
  
• Only phosphate fertilisers which comply with the industry limit of 280mg of cadmium per kg of P are used.
  
• Vegetated riparian buffer strips of sufficient width (10m - adjust for slope) to filter any run-off are maintained adjacent to all waterways.