Leaching of applied calcium and potassium from an oxisol in humid tropical Queensland

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Abstract
Downward movement of Ca and K applied to a north Queensland Oxisol has been studied in the field where rainfall is approximately 4000 mm per annum. After cultivating the soil to about 15 cm depth, Ca was applied as lime (5 tha-1) and gypsum (8.6 t ha-1) and K as potassium chloride (760 kg ha-1), the experiment being replicated five times. On three occasions, covering a six week period, known amounts of artificial rainfall (225 mm in total) were uniformly applied and, after 1 or 2 days, soil cores were taken to 1 m depth. Most of the Ca from the lime treatment remained in the top 10 cm but, in the gypsum treatment, Ca moved to about 30 cm. Potassium was extremely mobile in the profile and was rapidly distributed to about 50 cm depth. The hydraulic and electro-chemical properties of the soil were well characterized, and the observed movement of water and solute could be explained in terms of these properties.