Thermal properties of the root-zone media are very important physical factors that affect the energy balance and temperature distribution in the root-zone. Understanding the pattern of soil temperature is desired in helping make decisions as to when and how to apply water, fertilizers, chemicals, and soil amendments. The information also is important for predicting infestations such as weeds, diseases, and insect pests. The reason for this is that plant growth, fate of chemicals, and microbial population all are temperature dependent. Many of the turf management practices can affect the temperature and energy regime in turfgrass rootzones. The primary objective of this study, therefore, was to understand the thermal properties of sand-based media modified by inorganic amendments.

Treatments included the inorganic amendments calcined clay (Profile, Profile Products LLC, Buffalo Grove, IL.), calcined diatomaceous earth (CDE) (Axis, Eagle-Picher Minerals, Inc., Reno, NV), Zeolite clinoptilolite (ZeoponiX, Inc. Louisville, CO.), and polymer coated clay with a kelp material incorporated on the exterior of the polymer coating (PCC) (Bio-flex-a-clay, True Pitch Inc., Altoona, IA). Reed-sedge peat (Dakota Peat and Blenders, Grand Forks, ND) was used as a control because peat is commonly used as an organic amendment in golf greens. Inorganic soil amendments were oven-dried at 105º C for 24 hr before use. Fifteen percent of each inorganic amendment was mixed with 85% of sand (v/v). The mixtures were then filled into brass rings measuring 5.45 cm in diam. and 6 cm in length with a double cheesecloth layer attached to the bottom with a rubber band. The mixtures in the ring were then compacted following the USGA specifications. Each material had three replications. The sand mixtures were saturated from the bottom with water for 24 hr before they were set on a suction table. The suction table is a Plexiglas box with a sandwich of 10 cm of fine glass beads between the wire mesh at the bottom and a layer of block paper on the top, and a hanging water column connected to the bottom of the glass beads through a hole at the bottom of the box. Zero, -10, -25, -40, and -60 cm pressure head was applied to the suction table by positioning the outlet level of the hanging water column to the respective depth with reference to the top surface of the glass beads. At each pressure head, the volumetric water content and thermal properties were measured by a method and instrument established by Ren, Noborio, and Horton (1999). The volumetric water content was also measured at each pressure head by weighing the materials in the rings and weighing the oven-dried materials at the end of the experiment.

A field study was conducted at the Horticulture Research Station 15 miles to the north of Ames, Iowa. The green consisted of a 30 cm sand root zone placed over a 10 cm gravel blanket. No intermediate layer was used between the sand and the gravel blanket. A network of 10 cm diameter drain lines was trenched into the gravel blanket at 4.6 m intervals. The top 15 cm of sand from each plot was removed and combined with 5% peat on a volumetric basis. The field study consisted of a control with peat only and the 4 soil amendment treatments added at 10% on a volumetric basis. The treatments included calcined clay, CDE, ceramic, and PCC. The mixture was replaced on the plot area and allowed to settle during the winter. Treatments were replicated three times in a randomized complete block design with plots measuring 5 m². The area was seeded with 73 kg of 'Crenshaw' creeping bentgrass ha^-1 on 13 May 1997. Fertilizer was applied at seeding to supply 50, 90, and 80 kg ha^-1 of N, P and K, respectively. The treatment mixtures also were applied as topdressing once a year after establishment.

Copper-Constant thermal couples will be placed at the surface, 2.5, and 15 cm below the surface of the plots, respectively. The thermocouples will then be multiplexed to a data logger and the temperature will be recorded every 15 minutes. Water content of the profile will be measured with a TDR.

Thermal diffusivity (a ) will be estimated for the 15 cm depth by the phase angle lag method (Horton, 1983). The calculated values will be compared with that measured in the laboratory and used to predict numerically the soil temperature in the 15 cm profile.

The volumetric heat capacity measured at different water content agrees well with that calculated from volumetric water content and heat capacity of dry materials (Fig. 4 and 5). Notice, however, that the volumetric heat capacity was under estimated for sand over a large range of water content (Fig. 6).

The a values measured by the thermal-time domain reflectometry probe at different water content are shown in Fig. 7 and 8.

The study showed clearly that inorganic soil amendments commonly used in golf course root-zone media can affect the soil thermal properties and cause different temperature status. Such temperature changes may be predicted based on the surface temperature and water content measurement. Furthermore, the thermal diffusivity curve established in the laboratory may be referenced for the prediction. The impact of the temperature difference caused by inorganic soil amendments on turfgrass growth, microbial activities, and chemical degradation in the rootzone needs further study.