AIR-FILLED POROSITY OF GOLF GREEN SAND MIXES

Abstract

The air-filled porosity of sand mixes for greens as recommended by the United States Golf Association (USGA) is calculated from the difference between total porosity and water content retained in soil columns at 40 cm tension. Recently, some researchers suggested that 30 cm tension should be used. Theoretically, it is difficult to define when and at what tension quick drainage from macropores will cease in soil mixes. However, it may be possible to determine the tension at which quick drainage has reached its steady condition. This can be done by evaluating water contents if no significant difference is found between tensions. The objective of this study was to compare water retentive capacity of sand mixes between the 30 and 40 cm tensions and to examine statistically at which tension water content in the sand mix remained steady. Four sands and 35 different sand mixes were arbitrarily selected for this study. All the selected sands met the USGA sand recommendations, but only the Shawneetown sand was used in the mixes. The amendments used in the mixes included peat moss, earthworm castings, treated steer manure, municipal and yard wastes and combinations of these organic materials. Following the USGA specifications, three soil columns (7.9 cm in diameter and 10 cm long) were constructed for each sand or sand mix. Soil water retention characteristics of the soil column were measured by using the hanging water column method. For all 39 sand mixes, the mean water retention between tensions 30 and 40 cm was 0.02 m3 m−3 (ranging from 0.004 to 0.061 m3 m−3). But, it decreased to 0.008 m3 m−3 (ranging from 0.001 to 0.041 m3 m−3) between 40 and 50 cm tensions. Duncan Multiple Range (DMR) test indicated that 63% of the sand mixes with water contents at 30 and 40 cm of tension were significantly different. The significant difference in water contents implies that water retained in the soil column did not reach its steady state. It was, however, less than 14% of the sand mixes had a water content indicating significant difference between tensions of 40 and 50 cm. At 50 and 60 cm, it was less than 8%. Therefore, 40 cm of tension should be used in the measurement of air-filled porosity. This is particularly critical for sand mixes with an organic amendment higher than 0.02 g g−1.