Predicting value of diagnostic soil properties on actual and potential cation exchange capacity (CEC) in andisols and andic soils

Abstract

Relationships between charge variation and diagnostic soil properties were studied in Andisols and andic subgroups of Inceptisols and Ultisols. Charge variation was calculated as the difference between “field” or actual cation exchange capacity (CECa), and potential CEC (1M NH₄OAc, pH 7). Methods used to estimate CECa (effective CEC, silver thiourea) were higly correlated. The relative charge variation was greater than 70% in Andisols with very low content of layer silicates. Active Al (Alo) was positively correlated with CEC‐NH₄ and negatively correlated with CECa. This result contributed to the explanation of the negative trend correlation observed between actual and potential CEC. The ratio CECa/Alo showed low values (<8) in Andisols. This parameter was also tested in 25 samples of Andisols described elsewhere. The predicting value of both Alo and CECa for a rough estimation of variable charge seemed apparent from the results obtained.