Generalmente, al determinar la acidez titulable a pH7 (AT_pH7) se coloca al suelo en una solución tampón de pH=7 y la acidez liberada se mide con álcali. No hay información comparativa de diferentes métodos analíticos utilizados en Uruguay. Se cuantificó la AT_pH7 por tres procedimientos: a) se agitó la mezcla acetato de calcio:suelo y se dejó reposar 16 horas, se filtró el extracto y la titulación a pH = 7 se controló con electrodo (AT_pH7_fil); b) igual al anterior pero se tituló el sobrenadante del extracto, sin filtrar (AT_pH7_sob); c) se hicieron cuatro extracciones sucesivas con acetato de bario, se filtró el extracto y se controló el pH = 7 con fenolftaleína (AT_pH7fen) como indicador. Consideramos los valores AT_pH7fen como referencia. Al comparar AT_pH7_sob con AT_pH7_fil consideramos a los primeros como indicador de referencia. El ajuste entre AT_pH7_sob y AT_pH7_fil fue satisfactorio. La diferencia promedio fue de 0,36 meq.100g-1, pero hubo diferencias de -1,00 a 1,70 meq.100g-1. No existió sesgo en las diferencias. Algunas fuentes de acidez pudieron permanecer en el sedimento y no fueron evaluadas al titular el sobrenadante. Las mediciones AT_pH7_fil sobreestimaron 0,73 meq.100g-1 el promedio de AT_pHfen. Los valores promedio de AT_pH_sob y AT_pHfen no difirieron. Las muestras tuvieron la misma clasificación acorde a su saturación en bases independientemente del método utilizado. Ni la medición del pH = 7 con electrodo en vez de con fenolftaleína, ni el mayor tiempo de extracción, ni tampoco la utilización de acetato de calcio como extractante introdujeron significativos errores de interpretación. El método AT_pH_fil tuvo precisión y exactitud aceptables.

Whwn measuring the titratable acidity to pH=7 (AT_pH7) the soil is placed down with a buffer solution of pH=7 and the amount of acidity released is quantified with alkali. There is no comparative information about different analytical methods used in Uruguay. The AT_pH7 was measured by three methods: a) the mixture calcium acetate:soil was stirred and allowed a 16 hours rest, the extraction was filtered, and titration at pH = 7 was controlled by electrode (AT_pH7_fil); b) the same as the previous method, but after a 16 hours rest the supernatant was titrated unfiltered (AT_pH7_sob); c) four successive extractions with barium acetate buffered to pH = 7 were done, the extract was filtered and titrated to pH = 7 using phenolphthalein (AT_pH7fen) as an indicator. The AT_pH7fen values were considered as reference. When comparing AT_pH7_sob with AT_pH7_fil the first were considered as reference values. The fit between AT_pH7_fil and AT_pH7_sob was satisfactory. The average difference was 0.36 meq.100g-1 but differences from -1.00 to 1.70 meq.100g-1 were observed. There was no bias in the differences. Some sources of acidity may have remained in the sediment and were not evaluated when titrating the supernatant. The AT_pH_fil overestimated the average AT_pHfen values in 0.73 meq.100g1. The average values of AT_pH_sob and AT_pHfen did not differ. The samples had the same classification according to their base saturation regardless of the method used. Neither the measurement of pH = 7 with electrode instead of phenolphthalein, nor the longest extraction time, or the use of calcium acetate as extractant introduced significant errors of interpretation. The AT_pH_fil method had acceptable precision and accuracy