MINERAL ELEMENTS IN TEMPERATE CROP AND PASTURE PLANTS .2. CALCIUM

Twenty-five annual crop and pasture plant varieties from 21 species were grown on a lateritic gravelly sand at Gidgegannup in Western Australia. Plant tops were sampled at three stages during the growing season and at maturity. This paper presents data for calcium contents of the tops. Calcium concentrations varied widely among species, and to a smaller extent with age and among plant parts at maturity. Species rankings varied only slightly among harvests. Herbs and all legumes except lupins maintained high calcium concentrations throughout the growing season. By contrast, the concentrations in grasses, and even more markedly in the cereals, were low in the young plants and declined further as the season progressed. Concentrations in lupins were intermediate in the first two harvests, but fell precipitously towards maturity to levels similar to those in grasses. Despite low overall levels in the mature plant, seeds of lupins were generally higher in calcium concentration than other legume seeds and several times as high as cereal grains. Calcium concentrations of plant tops correlated reasonably well with published data on cation exchange capacities (CEC) of roots when taken over the whole range of species, but within major plant groups the correlation was poor. It is suggested that, rather than signifying a causal relationship between root CEC and calcium concentration in the tops, the results may merely indicate that dicotyledonous plants tend to have high calcium concentrations and CEC values while monocotyledonous plants have low. It is also suggested that if any such causal relationship does exist, its origins are more likely to lie in the CEC properties of the tops than in those of the roots. © 1968 CSIRO. All rights reserved.