The objective of this study was to determine if the source of inorganic topdressing amendment has any impact on the rootzone temperature and the performance of creeping bentgrass putting greens.

Thermal properties of the root-zone media of turfgrass are very important physical factors that affect the energy balance and temperature distribution in the root-zone. Understanding the pattern of soil temperature is useful to make decisions as to when and how to apply water, fertilizers, chemicals, and soil amendments. It is also important information for predicting development of pest problems such as weeds, diseases, and insect pests. The reason for this is that plant growth, fate of chemicals, microbial population all are temperature dependent. Many of the turf management practices can affect the temperature and energy regime of the turfgrass rootzone. We are specifically interested in heat dissipation in the top 1/4" layer of the media applied as topdressing. We will assess the thermal properties by measuring the temperature difference between the top and the bottom layers in soil profile at certain water content conditions.

The experiment was initiated at the Horticultural Research Station, Ames, IA on 14 September 2000. The USGA-type sand based putting green used in this study was established in 1996 with ‘Crenshaw’ creeping bentgrass. On 14 September 2000 the study area was verticut at a 0.75 cm depth and overseeded with ‘Crenshaw’ creeping bentgrass at 2 lbs/1000 ft² to make the study area more uniform with the heavy topdressing treatments. Treatments of pure Profile, Quickdry, Zeolite, Axis, sand, and a mixture of sand and peat (90%/10% v/v) were applied at a topdressing depth of 0.5 cm. After topdressing N, P₂O₅, and K₂O were at the rate of 1, 0.5, and 0.5 lbs/1000 ft², respectively. The experimental design was a randomized complete block with six treatments and three replications. Temperatures were measured at three depths from the surface (0, 1, and 6 inches) for each plot via automated thermalcouples. Water content was measured with a time domain reflectometer (TDR). Diurnal heat transfer and temperature distribution in the top 15 cm of the root-zone was recorded and the data were used to predict thermal properties. Creeping bentgrass turf quality was evaluated at various stages of development on a 1-10 scale, 10 = best turf.

To become familiar with the thermal properties of the inorganic amendments, temperatures were taken in the spring of 2001 (Table 1). Only slight differences in maximum temperature were detected. For example the sand/peat material was approximately 2° C higher than any of the other materials tested. The effect of these slight, but cumulative, differences in temperature is not well understood. Our intent is to measure thermal properties during the summer when higher surface temperatures are anticipated. The question we are trying to answer is "Do the different topdressing materials have different abilities to dissipate radiation energy and does this in turn result in a benefit to the plant?"