Growth responses to various calcium sources in a yellow earth soil with low calcium status

Abstract

Different sources of calcium (carbonate, acetate, sulphate and silicate) were investigated with the aim of determining the nature of the response to lime that occurs on the yellow earths of northern Cape York Peninsula. Stylosanthes guianensis cv. Cook was grown in pots as the test plant in a calcium source x phosphorus rate experiment, which was harvested on three occasions. Initially each source, except CaSO4, increased soil pH and decreased extractable aluminium, but during the pot experiment, pH of all treatments decreased below that in the initial soil and extractable aluminium increased. No evidence was found of a calcium x phosphorus interaction, which might have been expected if aluminium was interfering with phosphorus uptake, nor was any effect found of calcium source or rate on phosphate sorption by amended soils. Dry matter yields responded to increased rates of application of calcium, and at the later harvests were closely related to calcium concentration in the dry matter. Aluminium concentrations in the plant tops (60-180 ¦g g-1) were not excessively high. It is concluded that the major response to 'liming' on this soil is in correcting calcium deficiency and not in overcoming an aluminium toxicity problem.