Response of two soya bean cultivars to manganese toxicity as affected by pH and calcium levels

Abstract

Two cultivars of soya bean (Glycine max) were grown in nutrient solution to test their response to manganese toxicity as affected by pH and calcium levels in the medium. Increasing calcium levels consistently decreased manganese concentration in the shoots, but only decreased manganese toxicity symptoms and increased yields between moderate and high levels of substrate calcium. It is suggested that the higher ammonium/nitrate ratio associated with the low calcium treatments, where part of the calcium nitrate was replaced with ammonium nitrate, more than nullified the effect of increased manganese in the shoots obtained from the low calcium treatments.

pH had little effect on concentrations of manganese, iron or calcium in the shoots or on the development of manganese toxicity symptoms. However, as pH increased at high substrate manganese levels, total dry matter yields significantly decreased and levels of manganese in the roots markedly increased. At least part of the greater root manganese at higher pH could have been in the precipitated form, while the increased retention of calcium in the roots may also have influenced manganese retention. Reasons for decreased yields at higher pH are discussed. Environmental conditions appear to have had sonic effect on cultivar response to manganese toxicity.