Effect of Sodium On Saturated Hydraulic Conductivity of Sand-Based Putting Green Root Zones.

The effect of exchangeable sodium percentage (ESP) on the saturated hydraulic conductivity of soils has been extensively studied, and it has been shown that sodium promotes clay swelling and dispersion, resulting in a loss of soil plasticity and a decrease in conductivity. The vast majority of the current literature focuses on soils with moderate to high clay contents, but putting greens that meet USGA specifications contain less than 3% clay by volume. The objective of this study was to test the effects of ESP on the saturated hydraulic conductivity of sand-based root zones with low clay contents. The minimum clay content c required for soil plasticity is calculated as:

                                                c = (e_g/1+e_g) – (p_mineral / (1+e_g)) * w

where e_g is the ratio of voids, w is the mass fraction of water, and p_mineral is the mineral density of the soil. Soils with clay contents less than c do not exhibit plastic behavior, and therefore should be unaffected by sodium. Soil profiles were blended in a double-barrel rotating mixer and packed into metal sleeves to a bulk density of 1.6 g cm^-3. Profiles were 80/20 blends by volume of calcareous sand and either sphagnum peat, peat humus, calcined clay, silt loam, or silty clay loam, and a 100% sand control was included. Soil profiles were saturated in solutions with ESP of 0, 15, 25, 50, or 75, and then washed with two pore volumes of DI water. Saturated hydraulic conductivity of the profiles was measured using an automated falling head permeameter. Saturated paste extractions and ammonium acetate extractions were performed following conductivity measurements. The hydraulic conductivity of soils with less than the critical clay content c required for plasticity was not affected by increasing ESP treatments. Only the silty clay loam soil, which exceeded clay content c saw a reduction in conductivity with increasing ESP.