Effect of Fertilizer Amendments, Bulk Density, and Moisture on Calcium and Magnesium Diffusion

Abstract

AbstractThe fertility of acid subsoils may be improved by the injection of fertilizer materials into narrow slits that can be cut in subsoils during tillage operations. Little information is available to describe the effects that soil properties and added fertilizers have on the diffusion of Ca2+ and Mg2+ in acid subsoils. Laboratory studies were conducted with an acid subsoil of a Marvyn sandy loam soil (fine loamy, siliceous, thermic, Typic Hapludult) to determine the effects of fertilizers, bulk density, and volumetric moisture (Θ) on the diffusion of Ca2+ and Mg2+. The soil was treated with either dolomitic limestone, NH4NO3, NH4H2PO4, Ca(H2PO4)2, or Ca(NO3)2. Limestone was applied at a ratio of 79 g kg−1, whereas the remaining treatments were applied to provide 2.64 g kg−1 of either NO‐3 or H2PO‐4. The rates were used to simulate the concentrations that would occur in the zone of injection if the amendments were injected into the subsoil under field conditions. Calcium diffusion coefficients (De) measured with a cation exchange resin paper method ranged from 2.4 × 10−9 cm2 s−1 in the check to 3.9 × 10−6 cm2 s−1 in the Ca(NO3)2 treatment, and counter De for Mg2+ ranged from 3.6 × 10−9 cm2 s−1 in the check to 5.1 × 10−6 cm2 s−1 in the Ca(NO3)2 treatment. All treatments increased De for Ca2+ and Mg2+ relative to the check. In general, De increased as the concentration of Ca2+ and Mg2+ in the soil solution increased, and as the proportion of the extractable cation associated with the solid phase decreased. Diffusion coefficients for Ca2+ and Mg2+ increased as Θ increased from 0.12 to 0.30. Calcium and Mg2+ De reached a maximum at a bulk density of 1.6 to 1.7 Mg m−3 and then decreased slightly as bulk density increased to 1.9 Mg m−3. Bulk density effects were more pronounced at soil‐water pressure head values <0.033 MPa.