Effects of Plowing Depth and Deep Incorporation of Lime and Phosphorus Upon Physical and Chemical Properties of Two Coastal Plain Soils after 15 Years

Selected soil properties were evaluated 15 years after installing various depth‐of‐plowing treatments on two Atlantic Coastal Plain soils which initially had tillage‐induced pans and low subsoil pH. In 1960, Norfolk sandy loam was plowed to depths of 18, 38, and 56 cm, and Wakulla loamy sand was plowed to depths of 18 and 56 cm. Prior to and during the plowing operation, specified amounts of dolomitic limestone and phosphorus were applied. In 1975, the following variables were measured for each depth‐of‐plowing treatment as a function of depth: bulk density; texture; 1/3‐ and 15‐bar water contents; available water; cone index; modulus of rupture; pH; extractable P, K, Na, Ca, and Mg; percent organic matter; and acidity. In addition, the soil water characteristic, in situ unsaturated hydraulic conductivity [ K (θ)], and infiltration rate were measured on 3.6 m 2 plots for each treatment. Soil strength increased and infiltration rate decreased as plowing depth increased, creating physical conditions more unfavorable for root growth. Incorporation of P and lime by deep plowing increased the levels of P, Mg, and Ca in the 18‐ to 38‐ and 38‐ to 51‐cm depths making chemical conditions more favorable for rooting. Deep plowing increased K (θ) at the 0‐ to 18‐ and 18‐ to 38‐cm depths at higher soil water pressures primarily due to higher volumetric soil water contents which resulted from higher bulk densities and finer textured material in the soil matrix.