MAGNESIUM IN TROPICAL AND SUBTROPICAL SOILS FROM NORTH-EASTERN AUSTRALIA .2. 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) statu s, was undertaken to study the response to applied Mg. Of the soils st udied, 20 were strongly acidic (pH(1:5 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 fo r 90% relative yield were 0.21 cmol(+)/kg of exchangeable Mg or 7% Mg saturation, whilst the critical (90% yield) plant tissue Mg concentrat ion (whole shoots) was 0.15%.