Thermal properties of sand-based rootzone media modified with inorganic soil amendments

Thermal properties of rootzone media are very important physical factors that affect the energy balance and temperature distribution in the rootzone. Little research has been conducted to evaluate the thermal properties of inorganic soil amendments and their effects on turf quality. The objective of this study was to determine the effect of peat, calcined clay (Profile), calcined diatomaceous earth (Axis), zeolite clinoptilolite, and polymer coated clay (Bio-flex-a-clay) on the thermal characteristics of a sand-based medium. The thermal properties of these amendments alone and mixed with sand were measured using a thermal-time domain reflectrometry (TDR) method at various water contents. The temperature effects of these amendments were evaluated in a field study where sand/inorganic amendment mixtures were used as rootzone media of a golf green. Volumetric heat capacities of the pure amendments were significantly different at oven-dried, -400 mm tension, and saturated conditions. When mixed at 85% sand and 15% amendments (v/v), the peat mixture had the highest heat capacity of 2.05 x 10(6) MJM(-3)C(-1), all other inorganic soil amendments/sand mixtures had higher heat capacity values than that of sand, which was 1.59 x 10(6) MJM(-3)C(-1) at -400 mm tension. Sand alone had the highest thermal diffusivity (9.20 x 10(-7) (MS-1)-S-2) and Axis had the lowest (7.43 x 10(-7) (MS-1)-S-2) at 400 mm tension. Although these thermal characteristics did not translate into differences in turf quality during most of the season, periodical temperature differences were detected in the rootzones. On August 12, 2001, maximum soil temperature at the rootzone surface reached 45.8 degrees C in the plot treated with Axis when the air temperature was 30.5 degrees C. Direct heat injury on the grasses as a result of those heat pulses was observed.