Comparing the Calcium Requirements of Wheat and Canola

Abstract

ABSTRACT Spring wheat (Triticum aestivumL.) is the major crop species grown in south-western Australia and no responses of wheat to applied calcium (Ca) have been obtained in field experiments though responses have been obtained in glasshouse pot studies for wheat grown on the predominantly sandy acidic soils of the region. Since the mid 1990s canola (oilseed rape, Brassica napus L.) has been grown in rotation with wheat and has often developed symptoms of Ca deficiency when grown on sandy acidic soils in the field. The Ca requirement of canola in these soils is not known and was measured and compared with Ca requirements of wheat in the glasshouse study reported here when 5 amounts of Ca (0–630 mg Ca/pot), as calcium sulfate, were applied. Application of Ca did not affect shoot production of wheat but increased grain yields by about 25% and 50 mg Ca/pot was required to produce 90% of the maximum grain yield. Two canola cultivars were grown, and both showed no shoot yield responses to applied Ca at early growth (GS1.5). However, at flower bud visible (GS3.5) shoots of triazine tolerant canola cv. ‘Karoo’ showed about 17% increase to applied Ca and required ∼47 mg Ca/pot to produce 90% of the maximum yield, while corresponding values for cv. ‘Outback’ were 42% and 185 mg Ca/pot. Both canola cultivars showed large seed (grain) yield responses to applied Ca. Canola cv. ‘Outback’ produced no grain when no Ca was applied and showed ∼ 97% increase to applied Ca and required about 462 mg Ca/pot to produce 90% of the maximum grain yield. The triazine tolerant cv. ‘Karoo’ produced about 22% of the maximum grain yield when no Ca was applied, showed approximately 78% grain yield response to applied Ca and required about 475 mg Ca/pot to produce 90% of the maximum grain yield. However, to produce 50% of the maximum grain yield, cv. ‘Outback’ required 250 mg Ca/pot while cv. ‘Karoo’ required about 100 mg Ca/pot. The grain yield response curve for cv. ‘Karoo’ was exponential and that for cv. ‘Outback’ was sigmoid so differences in the response curves were largest when small amounts of Ca were applied and decreased as more Ca was applied. Evidently canola cultivars differ in their ability to access soil and applied Ca providing opportunity to breed and select cultivars efficient at accessing soil and applied Ca. For both wheat and canola the concentration of Ca in dried shoots increased as more Ca was applied and, for each amount of Ca applied, the concentration of Ca in shoots decreased as plants matured. Both canola cultivars consistently had larger concentrations of Ca in shoots than wheat, either when no Ca was applied and for each amount of Ca applied, suggesting canola roots were better able to access soil and applied Ca than wheat roots. The Ca concentration in young wheat (GS15) and canola (GS1.5) shoots that was related to 90% of the maximum grain yield (critical Ca concentration) was 0.33% for wheat and 2.5% for both canola cultivars.