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The pH Dependency of Aluminum Phytotoxicity Alleviation by Calcium Sulfate
Author(s) -
Noble A. D.,
Sumner M. E.,
Alva A. K.
Publication year - 1988
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1988.03615995005200050036x
Subject(s) - phytotoxicity , chemistry , toxicity , calcium , sulfate , glycine , nutrient , soil ph , nuclear chemistry , horticulture , soil water , biochemistry , amino acid , biology , ecology , organic chemistry
The alleviation of Al toxicity by CaSO 4 is partly due to an increase in formation of less phytotoxic AlSO + 4 species. Since ion‐pair formation is dependent on the solution pH, the magnitude of alleviation of Al toxicity by CaSO 4 may be influenced by pH. In the present study, the alleviation of Al toxicity (80 µ M ) to soybean [ Glycine max (L.) Me root growth by CaSO 4 (625–10 000 µ M ) was investigated in dilute nutrient solutions at pH 4.2 or 4.8. The concentration of monomeric Al (by a modified aluminon technique) in these solutions ranged from 69.3 to 77.7 µ M . An increase in CaSO 4 in solution (625–10 000 µ M ) increased the root length by 3‐ and 2‐fold in solutions at pH 4.2 and 4.8, respectively. The predicted activity of Al 3+ decreased while that of AlSO + 4 increased with an increase in added CaSO 4 . The magnitude of alleviation of Al toxicity by CaSO 4 was smaller at pH 4.8 than at pH 4.2. This pH dependency is due to lesser formation of AlSO + 4 at pH 4.8 than at pH 4.2, together with an increase in formation of Al(OH) + 2 at pH 4.8. Root length was poorly correlated with the predicted activity of Al 3+ ( R 2 = 0.346) or sum of the activities of Al 3+ , hydroxy‐Al, and AlSO + 4 species ( R 2 = 0.366). However, the relationship was improved when the sum of the activities of Al 3+ , Al(OH) 2+ and Al(OH) + 2 species was considered ( R 2 = 0.624) and further improved ( R 2 = 0.841) when the activities of these species were corrected for their respective valence. A good correlation was also found ( R 2 = 0.88) between root length and calcium aluminum balance; CAB = [2log( a Ca 2+ )] − [3log( a Al 3+ ) + 2log( a Al(OH) 2+ ) + log ( a Al(OH) + 2 )] index.