ABSTRACT
Soil chemical properties play an important role in nutrient uptake and plant growth. The exchange capacity (EC) of soils is important because many plant nutrients are absorbed and held in the exchangeable form until utilized by plants. The amount and type of EC of a soil depends upon the clay mineralogy, amount of clay, pH, and humus content of the soil. Colloids are primarily responsible for the chemical reactivity in soils. Each colloid has a net negative (−) charge and attracts and holds positively (+) charged particles. Cation exchange capacity (CEC) refers to the quantity of negative charges existing on the surfaces of clay and organic matter. Anions are negatively charged and held by soil particles with net positive charge. Acidity in soils comes from H+ and Al3+ ions in the soil solution and sorbed to soil surfaces. The desirable pH range for optimum plant growth varies among crops. Liming neutralizes soil acidity and gypsum is used to correct aluminum problems in the subsurface soil layers. Sodic soils exhibiting poor physical and chemical properties impede water infiltration, availability, and plant growth. Calcareous soils are those containing enough free calcium carbonate (CaCO3) and regarded as an alkaline (basic) soil.
