A New Method for the Simultaneous Measurement of pH‐Dependent Cation Exchange Capacity and pH Buffering Capacity

Abstract

The pH dependent cation exchange capacity (CEC) and pH buffering capacity (pH BC) are two crucial properties in soil fertility management of variable charge soils. However, they are rarely measured, since most of the existing methods are cumbersome and time‐consuming. We propose a new method, based on the silver‐thiourea (AgTU) method, for the simultaneous measurement of pH dependent CEC and the pH BC. In general, this method consists of first increasing the pH of the soil to about pH 7 and then gradually acidifying the soil by titrating with HNO3, while measuring pH and CEC after each equilibration. This way, both CEC at different pH values and the pH BC are measured on the same sample, without the multiple washing steps needed in other procedures. Various aspects of the proposed method were tested and the results obtained were compared with the ion adsorption method. The modified AgTU method obtains field relevant results and is suitable for the routine analysis of large numbers of samples.

Artificial Neural Network Approach for Predicting Cation Exchange Capacity in Soil Based on Physico-Chemical Properties

“…Since soils have pH-dependent charges in both temperate and tropical regions, and the number of negative charges on the soil colloids increases with the increase of pH, thereby causing CEC to increase, CECs of variable-charge soils are often expressed as a function of pH and the electrolyte concentration (Katou, 2002;Oorts et al, 2004). Horn et al (2005) compared two regression-based PTFs for soil CEC, showing strong correlations of pH, clay content, and organic carbon content with CEC.…”

Capacidad de intercambio catiónico: descripción del método de la tiourea de plata (AgTU+n)

“…Este método se basa en la afinidad del complejo AgTU + n sobre la matriz arcillosa. La CIC se determina por diferencia entre la concentración inicial y el remanente de la solución saturante de AgTU + n, mediante espectrometría de adsorción atómica (Cremers y Pleysier, 1973;Xing-Cun, 1998;Ahmad et al, 2002;Oorts et al, 2004).…”

“…This method is based on the affinity of the complex AgTU + n on the clay matrix. The CIC is determined by the difference between the initial concentration and the remaining of the saturating solution of AgTU + n by atomic adsorption spectrometry (Cremers and Pleysier, 1973;Xing-Cun, 1998;Ahmad et al 2002;Oorts et al, 2004).…”

“…En pH alcalino se forman precipitados de Ag2O (Kan-Sen et al, 2005), de manera similar el AgTU + n es inestable a pH>8 (Cornell y Aksoyoglu, 1991). Algunos autores han modificado esta técnica para prolongar la estabilidad de AgTU + n, como: Oorts et al (2004) que incrementaron el pH del suelo antes de la adición de AgTU + n, con una solución de NaOH 0.001 M, hasta llegar a un pH de 8 y 9, esta modificación tuvo resultados similares al AgTU + n amortiguado con acetato de amonio. Dhorman (2006) propone que la solución AgNO3 sea adicionada lentamente, durante 2 min, mientras se agita la solución de TU, después se agrega la solución de acetato de amonio.…”

“…In alkaline pH, precipitates of Ag2O (Kan-Sen et al, 2005) are formed, similarly AgTU + n is unstable at pH> 8 (Cornell and Aksoyoglu, 1991). Some authors have modified this technique to prolong the stability of AgTU + n, such as: Oorts et al (2004), which increased the pH of the soil prior to the addition of AgTU + n, with a 0.001 M NaOH solution, until a pH between 8 and 9 was reached. The results similar to AgTU + n buffered with ammonium acetate.…”