Magnesium in tropical and subtropical soils from north-eastern Australia. II. Response by glasshouse-grown maize to applied magnesium

A glasshouse trial, in which maize (Zea mays L. cv. Pioneer 3270) was grown in 35 north-eastern Australian soils of low magnesium (Mg) status, was undertaken to study the response to applied Mg. Of the soils studied, 20 were strongly acidic (pH1:5 soil : water <5·4), and in these soils the response to Mg was studied in both the presence and absence of lime. Magnesium application significantly (P < 0·05) increased dry matter yield in 10 soils, all of which were strongly acidic. However, significant Mg responses were recorded in 6 soils in the presence of lime, indicating that, in many situations, liming strategies may need to include consideration of Mg nutrition. Critical soil test values for 90% relative yield were 0·21 cmol(+)/kg of exchangeable Mg or 7% Mg saturation, whilst the critical (90% yield) plant tissue Mg concentration (whole shoots) was 0·15%.