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Do you need lime and potassium? Apply both

Large areas of West Australian cropping soils have low potassium (K) reserves. Acidity also constrains most of these soils.  Potassium deficiencies have become more widespread with intensive cropping, removal of hay or stubbles, and K fertiliser inputs lower than removal rates.

James Easton is the Field Research Manager with CSBP in West Australia. Starting in 2011, CSBP have been running trials to look at the impact of liming on K requirements.

While yield responses to lime would be expected to increase K removal rates, there was a need to understand if lime had an effect on soil K availability. We considered two possibilities:

  • liming could increase soil K availability by improving root development
  • calcium supplied from lime could displace K and move it down the soil profile.

Nothing special in the first 5 years

The lime treatment plots received 3 t/ha in 2011, and 2.6 t/ha in 2014. In the first 5 years of the trial results across a range of fertiliser regimes showed:

  • no yield response to lime.
  • no impact of lime on the K response curve or K uptake.

Crops responded to K fertiliser through increased hectolitre weights and reduced screenings. Without K fertiliser the wheat produced in most seasons was downgraded to GP1. The increased vigour of crops in K fertilised plots reduced the ryegrass population.

Six years on the lime kicked in

In 2016 we started to see a yield response to the lime treatments. We’re expecting higher yields to increase K demand. CSBP will continue to monitor to see how well  soil and fertiliser K can meet crop demand.

A graph comparing soil pH to depth between limed and unlimed treatments.

The soil pH profile in December 2016.

What to do

Growers and advisors should soil test to monitor soils for both low pH and low K. Both lime and K fertiliser are needed if soil tests show low pH and low K. Maintain normal K fertiliser regimes in the first few years after liming. Increasing yield potential will increase long term K fertiliser requirements for the crop.


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