The movement of calcium and magnesium in selected Virginia soils from surface applied dolomitic limestone

Abstract

Surface (0-20 cm) dolomitic limestone treatments of 0, 4.48, 8.96, and 13.44 Mg ha⁻¹ on the Coastal Plain and up to 17.92 Mg ha⁻¹ on the Piedmont and Ridge and Valley soils were made to seven acid Virginia soils. These amendments were made to document movement of Ca and Mg as well as neutralization of soil acidity within these soil profiles. During the fourth growing season following application, samples in 5 or 10 cm increments were taken to a depth of 60 cm. Soil chemical properties (soil water pH, soil mol L⁻¹ KCl pH, exchangeable Ca, Mg, and Al) were determined.

Calcium and Mg movement and depth of neutralization decreased as soil clay content increased. These cations moved through the sampling depth in the coarse-textured Emporia loamy sand, but neutralization was only evident to the 50 cm depth. The Pacolet sandy clay loam, with the high percentage of clay in the surface horizon, showed no movement of Ca from the surface layer and Mg movement was limited to 25 cm. Liming increased pH dependent CEC which increased cation retention in the horizons receiving direct lime application. Depth of neutralization was lime rate dependent with higher rates resulting in greater acidity neutralized. The Pacolet soil illustrated increasing water pH values to the 25 cm depth, in comparison to the subsoil at the 8.96 and 17.92 Mg ha⁻¹ rates of lime application.

Magnesium movement was detected at greater depths than Ca in all soils. Neutralization of acidity did not accompany Mg movement, demonstrating that the cation moved as a neutral salt.

Results indicate that subsurface chemical properties will be affected in soils cropped in continuous corn or corn-soybean rotations as opposed to crops of continuous alfalfa. Despite cation movement in the profile, neutralization of acidity may not occur beyond the plow layer, i.e. the Frederick silt loam or may occur to a depth of 50 cm, i.e. the Emporia loamy sand, with the other soils being intermediate.