How Do Cations Exchange in The Soil?

This lab focuses on estimating the cation exchange capacity (CEC) in soils, which is a proxy of its fertility and ability to hold nutrients. Cation exchange occurs when cations in solution replace adsorbed cations on clay and humus particles, which have negative charges on their surfaces and can attract and retain cations. The lab involves filtering soil samples with 0.2 N KCl and distilled water and testing the filtrates for calcium using saturated ammonium oxalate. Soils rich in clay, organic matter, and humus have high CEC, while sandy soils have low CEC and are prone to leaching losses. Adding organic matter to the soil is an effective way to increase CEC and nutrient retention.