EXCHANGEABLE CATION ANALYSIS OF SALINE AND ALKALI SOILS

Abstract

Consideration of various factors involved in the exchangeable cation analysis of saline and alkali soils led to the development of the following scheme of analysis: Step 1. Extract a sample of the soil with an excess of neutral 1 [image] ammonium acetate soln. and determine the amts. of the various cations removed. Step 2. Prepare a saturation extract of the soil and determine its soluble cation contents. Step 3. Calculate the exchangeable cation contents of the soil by subtracting the soluble cation contents from the amts. of the various cations extracted by the NH4AC soln. Step 4. Determine the cation-exchange capacity by measuring the amt. of Na adsorbed by a second sample upon treatment with an excess of 1 [image] Na acetate soln. having a pH value of 8.2. Na rather than NH4 is employed for the detn. of cation-exchange capacity because possible fixation of NH4 in difficultly exchangeable form is thereby avoided, no correction for the presence of Ca carbonate is required, and the displaced cation can be detd. rapidly and accurately by means of a flame photometer. The opt. number of NH4 Ac extractions for the removal of exchangeable and soluble cations was detd. to be 3 or 4. The number of Na acetate treatments required for saturation of the soil exchange complex with Na was 4. In the washing of Na-saturated soil with ethanol, errors from hydrolysis and excess Na salt were balanced most closely at 3 washings. Variations in pH and the solubility of Ca carbonate in the Na acetate soln. had negligible effects upon cation-exchange capacity values.