LIME RESPONSES BY BARLEY AS RELATED TO AVAILABLE SOIL ALUMINUM AND MANGANESE

Twenty-three surface soils (0-10 cm) sampled from major New South Wales lime trials were incubated at six lime rates, from 0 to 10 t/ha, and used in pot trials with barley (Hordeum vulgare cv. Schooner) which was grown for five weeks. Each replicate pot was soil tested for exchangeable cations (Ca, Mg, K, Na, Mn, Al), pH in 0.01 M CaCl2, and Al in the 0.01 M CaCl2 extract by pyrocatechol violet (total Al) and by reaction for 15 s in 8-hydroxyquinoline (monomeric Al). The latter was also converted to the activity of Al3+ in the 0.01 M CaCl2 extract. The soil tests were compared for their prediction of the dry matter yield of whole tops of barley. The four tests for aluminium (exchangeable Al as Al/ECEC; total 0.01 M CaCl2 extractable Al; monomeric 0.01 M CaCl2 extractable Al; and Al3+ activity in 0.01 M CaCl2) were each better indicators of the infertility of the acid soils than soil pH. The prediction of the dry matter yield of barley by the four aluminium tests was improved by the inclusion of exchangeable soil manganese in the statistical analysis. The use of 0.01 M CaCl2 is recommended as a routine extraction procedure for diagnosing Al toxicity. Soil Mn should also be measured and included in correlations with barley growth. Pyrocatechol violet is the recommended analytical procedure for Al owing to its comparative simplicity.