Fertiliser trial results put into practice

Fertiliser trial results put into practice

Cropping News
Rob McFerran (left) and host farmer Rob Bell discuss the outcomes of the fertiliser trials in the South West.

Rob McFerran (left) and host farmer Rob Bell discuss the outcomes of the fertiliser trials in the South West.

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The fertiliser industry has been a major partner in the State government's uPtake program that has established 32 phosphorus (P) fertiliser trials on grazing land across the South West over the past two years.

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INCREASED confidence in the science supporting phosphorus application has seen major fertiliser companies incorporate the recent findings in the models they use to generate fertiliser advice for farmers.

The fertiliser industry has been a major partner in the State government's uPtake program that has established 32 phosphorus (P) fertiliser trials on grazing land across the South West over the past two years.

Nineteen trials were established in 2019 and some of these were rolled over to this year where 13 trials were conducted across the greater South West (Peel-Harvey to Oyster Harbour catchments) to examine the P response of pastures.

Trials were established on soils with low to high P buffering index (PBI) and with varying soil P levels.

Pasture growth was measured in response to Ps applications ranging from 0-40 kilograms per hectare, both with and without basal nutrients, nitrogen, potassium, sulphur and trace elements.

The information from these trials contributes to defining the relationship between the amount of P in the soil and pasture growth.

The amount of P in the soil measured by a soil test to achieve a target production level is called the critical value.

Critical values for soils with low to high PBI have been reported previously from similar trial data managed through the national Better Fertiliser Decisions for Pastures project.

The uPtake project aims to assess how relevant the national data and critical values are for South West soil types and contemporary pasture species.

A fertility index (soil test value divided by the critical value) is being used to compare trial results with expected results based on national data.

A fertility index of one (soil P the same as critical value P) is considered optimal.

Thirty two phosphorous fertiliser trials have been run across the South West over the past two years.

Thirty two phosphorous fertiliser trials have been run across the South West over the past two years.

For a Fertility Index 1 or greater no pasture response to P is expected and for soils with a fertility index of less than 1 a pasture response to P is expected.

What this means to farmers

  • Results from trials to date show that the national critical values for P used to inform P fertiliser recommendations are relevant to the South West.

You can therefore have confidence that P fertiliser recommendations based on critical values from BFDP are appropriate.

  • If your soil test shows that your soil contains excess P for your target production levels, (i.e fertility index greater than 1), adding more P will not increase productivity.

Adding more P will unnecessarily increase costs and may escalate P movement into waterways, contributing to algal blooms.

  • If your P soil test shows a fertility index of 1 at the start of the season, then it should contain sufficient P for seasonal pasture growth.

Soil testing should guide subsequent pasture P requirements.

  • Addressing limiting nutrients in your soil (for example nitrogen, sulphur, potassium, micro nutrients) and correcting low pH can dramatically increase production and minimise unnecessary losses of nutrients to the environment.
  • Soil testing and comparison with critical values is essential to determine the nutrient requirements of your soil to meet your production targets.

The uPtake project will run to June 2023 and aims to undertake at least 36 P response trials across the South West.

Results from the next two years of trials will be added to the 2019/20 trial data to build a robust validation of national data and enhanced understanding of P responses in South West WA soils with contemporary pasture species.

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