ANALYSIS OF ACID-SOIL STRESS IN SORGHUM GENOTYPES WITH EMPHASIS ON ALUMINUM AND MAGNESIUM INTERACTIONS

Acid-soil stress in 12 sorghum (Sorghum bicolor (L.) Moench) genotypes was attributed mainly to aluminium (Al) toxicity. Root damage and mag nesium (Mg) deficiency are two independent aspects of plant sensitivit y to Al, either in acid soil or in nutrient solution. At moderate soil acidity, Mg deficiency dominantly limited growth whilst at high acidi ty root damage overruled the effect of Mg deficiency on the growth res ponse. In nutrient solutions containing Al, increased Mg supply improv ed both root development and Mg nutrition of plants, whereas increased calcium (Ca) supply, or nutrition with ammonium (NH4) instead of nitr ate (NO3), alleviated root damage but amplified Mg deficiency. At lowe red pH the syndrome of Al toxicity was more profound. The implications of Mg-Al interactions, root damage, Mg supply and genotype selection are elucidated.