Thick Bh Horizons in the North Carolina Coastal Plain: II. Physical and Chemical Properties and Rates of Organic Additions from Surface Sources

Abstract

Abstract Thick Bh horizons in siliceous sands of the North Carolina Coastal Plain have essentially no extractable iron, and very small quantities of calcium, magnesium, and potassium. Aluminum is the dominant cation and the exchange properties of the Bh horizons are dominated by Al and organic carbon. One to two grams of total Ca, Mg, and Na/m 2 per yr are being added to these soils by rainfall and recycling. From 3 to 40 g of carbon/m 2 per yr is available to move into the solution below 10 cm. This is enough carbon to develop a Bh horizon 7 m thick in < 30,000 years. The mechanism that immobilizes the carbon to form the Bh horizon is open to question. It is postulated that bases, pH changes, or other aspects of the chemical environment may have immobilized the carbon initially, but these causes have subsequently been removed or changed through leaching. Another alternative, is organo‐mineral bonding such as with silica on quartz surfaces that may be the major factor in the immobilization of carbon.