A comparison of slow release potassium fertilisers for pasture

Abstract

Luxury uptake of potassium (K) from potassium chloride (KC1) by pasture plants is a major disadvantage in its use as a fertiliser for pastures. Luxury uptake shortens the fertiliser's effective life and causes excessively high concentrations of potassium relative to calcium, magnesium, and sodium. This can result in health problems for grazing stock. A further disadvantage is that KC1 is readily leached from the soil if there is heavy rain. Coating KC1 has been tried as a way of slowing the release of K and its uptake by ryegrass, and of reducing loss by leaching. Coating KC1 with sulphur reduced its rate of dissolution greatly and avoided luxury uptake by the grass. On an extremely K deficient soil there was some loss of growth relative to uncoated KC1 for 2 months, but over the next 4 months, the sulphur-coated KC1 gave higher yields. Wax-coated KC1 gave practically the same results as uncoated KC1. A leaching test was used to measure rate of solution of KC1 and its results related well to the reduction of luxury uptake.

Keywords:

• potassium fertiliser
• slow release fertilisers
• pasture
• luxury uptake
• cation ratios
• leaching
• ryegrass