With cropping systems exporting more nutrients to the grain terminal than ever before due to the combination of higher yields and higher cropping intensities, soil reserves will decline unless grain growers are replacing those nutrients.
Experts warn that although trace element deficiencies have not been prevalent, many farmers are not using sufficient trace element additions to their soils so deficiencies may occur in the future.
Adequate trace element nutrition is just as important for vigorous and profitable crops and pastures as macro element nutrition, such as nitrogen or phosphorus. The difference is that crops only require trace elements in minute amounts. Balanced nutrition of all essential elements ensures good returns on investments in fertilisers.
Dr Nigel Wilhelm from the South Australian Research and Development Institute (SARDI*) says southern Australian cropping soils are more likely to be deficient in zinc, copper and manganese than other trace elements.
“Of these three, zinc deficiency is probably the most important because it occurs over the widest area,” said Dr Wilhelm, whose research is supported by the Grains Research and Development Corporation (GRDC).
“Zinc deficiency can severely limit annual pasture legume production and can reduce cereal grain yields by up to 30 per cent.”
Zinc deficiency has been identified on many soil types. Acid sandy soils, sandy duplex soils, red-brown earths, “mallee” soils and calcareous grey and red heavy soils have all had either zinc responses confirmed or crops have been identified with zinc deficiency symptoms.
Speaking at GRDC Grains Research Updates, Dr Wilhelm said zinc deficiency appeared to be equally severe in both high and low rainfall areas.
Copper deficiency is also important because it is capable of causing total crop failure. Under conditions of severe copper deficiency, cereal plants may have leaves which die back from the tip and twist into curls.
Manganese deficiency is more likely to be a problem on alkaline soils, however, responses to manganese have also been recorded on impoverished, acid to neutral sandy soils.
“The availability of manganese is also strongly affected by seasonal conditions and the availability is lowest during a dry spring.”
Dr Wilhelm said if these trace elements were not managed well, the productivity of crops and pastures could be reduced and further production could be lost through secondary effects such as increased disease damage and susceptibility to frost.
He said trace element deficiencies were difficult to diagnose with soil tests or from plant symptoms.
“Plant testing is the most reliable, if not fool-proof, tool to diagnose trace element deficiencies.
“Foliar sprays will usually correct a problem in-crop. However, for long-term correction of the deficiency, boosting soil reserves is a sound investment.”