Micronutrient Deficiencies in Australian Field Crops

Australia’s ancient landscape has soils of exceptionally low fertility and deficiencies of all known nutrients have been recorded. Deficiencies of Mo and Zn are most widespread, being common on acid and alkaline soils respectively. Zinc deficiency is notable for being the most widely distributed micronutrient problem globally as well as in Australia, occurring on all soil classes, acid and alkaline, sandy and clayey, humid and arid, and in hot and cold growing seasons. Many Australian soils are affected by the presence of fine, free lime in the form of shellgrit blown up over the continent when sea levels were low during the last ice age; such soils, especially the more sandy types are low in micronutrient cations, Fe, Zn, Mn, Cu and/or Co. Multiple nutrient deficiencies are common, giving rise to a wealth of nutrient interaction effects. Interactions between two or more micronutrients and between micro- and macro-nutrients are agronomically and economically important. The classical micronutrient sensitivities reported elsewhere are also seen in Australia, but importantly, breeding has been carried out for tolerance to deficient soils in the major cereal crops, as well as tolerance to the common nutrient toxicities, the latter in common with activities in many parts of the world. The first deliberately bred cereal variety (barley) tolerant to Mn deficiency was released in South Australia in 2004. An important feature of the agronomy of micronutrients is the yield benefit in micronutrient-deficient soils of sowing seeds with a high micronutrient density. The use of plant analysis for diagnosis is almost always warranted as some crop varieties may lose much yield potential before symptoms of some micronutrient deficiencies appear. Recent research in South Australia has demonstrated that on calcareous soils, multi-nutrient fluid fertilisers have provided more efficient responses to both macronutrients and micronutrients than granular fertilizers.