Characterization, classification, and productivity studies of typic hapludult mapping units in the southern Piedmont of Virginia

Two studies were initiated in the Virginia southern Piedmont to assess characterization, classification, and productivity of soils mapped as Cecil-Pacolet (clayey, kaolinitic, thermic Typic Hapludults). Effects of erosion on Ap and Bt soil properties and soybean grain yields were studied in Pittsylvania and Lunenburg counties. Relationships between soil properties, soybean yields, and erosion classes were not observed until the soils became severely eroded. Water contents at -10kPa and -1500kPa increased as clay content increased but plant available water remained at 0.09 m³ m⁻³ across erosion classes. Available phosphorus (P) decreased with severity of erosion and was significantly correlated with soybean yield. The highest grain yields were on slightly and moderately eroded soils and were attributed to available P levels above 18 mg P kg⁻¹ critical level for optimum crop production. Low yields on the severely eroded sites corresponded to available P below 18 mg kg⁻¹.

A second study on composition and variability of the Cecil-Pacolet map unit in Appomattox County showed large variation in soil properties and taxonomic classes. Variability is attributed to intrusions of mafic materials in the map unit. Variability was extreme within delineated soil bodies and was reflected in taxonomic classification in which up to six taxa can occur within the same delineation. Cecil and Pacolet soils comprise 62 percent of the map unit. Similar soils comprise 70 percent of the map unit and dissimilar soils make up the remaining 30 percent. The map unit is named Pacolet-Cecil and dissimilar soils are included in the mapping unit description.