Cation Exchange Capacity

CEC measures how many positively charged nutrients (calcium, magnesium, potassium, ammonium) a soil can retain on clay and organic matter surfaces. Sandy soils have low CEC (1–5 meq/100g), while clay soils and humus-rich soils have high CEC (20–50+). In raised beds and containers, adding compost and biochar increases CEC, reducing how quickly nutrients leach out during watering.