Austauschkapazität

Austauschkapazität refers to the total amount of exchangeable cations that a soil can hold. It is a crucial soil property that influences nutrient availability, soil structure, and the soil's ability to buffer against changes in pH. This capacity is primarily determined by the amount and type of clay minerals and organic matter present in the soil. Clay particles and organic matter have negatively charged surfaces that attract and hold positively charged ions, known as cations.

The cations most commonly found in exchangeable form include calcium (Ca²⁺), magnesium (Mg²⁺), potassium (K⁺), and sodium (Na⁺), as well as essential plant nutrients like ammonium (NH₄⁺). When plants require these nutrients, they can release hydrogen ions (H⁺) from their roots, which then displace the nutrient cations from the soil's exchange sites and make them available for uptake. A higher Austauschkapazität generally indicates a more fertile soil because it can retain a greater supply of essential nutrients.

Austauschkapazität is typically measured in milliequivalents per 100 grams of soil (meq/100g) or centimoles of positive charge per kilogram of soil (cmol+/kg), with the latter being the internationally recognized unit. Soils with a high clay content or a significant amount of organic matter will have a higher Austauschkapazität compared to sandy soils, which have fewer charged surfaces. This property also plays a role in the soil's buffering capacity, helping to resist drastic changes in soil acidity or alkalinity.