Plant growth on a low calcium status solodic soil in a subtropical environment

Abstract

The importance of calcium in legume growth and soil fertility in temperate regions is well known, but there is evidence that in tropical regions adequate legume growth may be obtained under conditions of low calcium status. These differences require further elucidation for a subtropical environment, particularly as both temperate and tropical species occur and climatic conditions are transitional between temperate and tropical regions. Large areas of solodic soils of very low calcium status occur in southern Queensland. Volunteer plant growth is poor and sparse. In considering the use of legume species to increase the amount of nitrogen in the soil–plant system the possible effect of low calcium status assumes importance. Investigations were carried out on a solodic soil from Tara, Trifolium repens L. and Phaseolus lathyroides L. being used as representative of temperate and tropical legumes respectively. Initial nutrient studies showed an extreme phosphorus deficiency. Even with adequate phosphorus supplied as sodium dihydrogen phosphate, however, yield of the temperate legume was poor. This was due to the existence of soil conditions which could be ameliorated by the application of calcium carbonate (lime). Interactions between legume species, nutrient elements, and lime were observed. Lime with zinc substantially increased the yield of T. repens. Smaller increases were obtained with P. lafhyroides; in the absence of zinc, lime depressed the yield of this species. The sulphur treatment decreased soil pH, but a positive lime=sulphur yield interaction was obtained. A copper deficiency in T. repens uncomplicated by lime interaction was found. There was no evidence of molybdenum deficiency or of a molybdenum-lime interaction. The beneficial effects of lime are considered to be associated with both calcium deficiency and mineral element toxicity. The possible effect of climatic factors on both zinc deficiency and aluminium toxicity in relation to temperate and tropical legumes is discussed. A range of 48 species and strains of temperate legumes also showed marked responses to lime on this solodic soil, although differences were observed between species and genera. The role of calcium in superphosphate and the multiplicity of effects associated with the use of this fertilizer emphasize the difficulty of interpreting field responses and of attributing response to any one factor.