Chronic dry spots often occur on the upper reaches of slopes on golf putting greens constructed with sand-based root zones, in part because water is quickly wicked downslope through the root zone after irrigation or rainfall. Lower water contents in dry spots are associated with higher matric (capillary) water tensions that generate increased stress in the turfgrass surface, leading to increased maintenance operations and costs such as those associated with frequent hand watering. Lower water contents also provide an environment favorable for development of water repellent solids in the root zone, a condition that reinforces the tenacious nature of dry spots (Ritsema et al., 2004; Wilkinson and Miller, 1978).
Because retention of water decreases with increases in matric water tension and matric water tension generally increases with elevation from the base of the root zone, one means to maintain consistent water content in the upper portion of the root zone on slopes is to decrease the depth of the root zone with distance upslope. Although this modification can be used successfully to increase near surface water content on slopes (Frank et al., 2005; Leinauer et al., 2001), the amount of water stored in the profile decreases with distance upslope and to an even greater degree than on slopes without modification. To maintain consistent water content in the upper portion of the root zone while at the same time maintaining an adequate amount of water stored in the profile, water-holding amendments such as calcined clay may be added and varied with position on the slope or the particle size distribution of the sand in the root zone mixture may be varied with position on the slope. Although these latter modifications are effective (Bigelow et al., 2004; Li et al., 2008; Taylor et al., 1997), varying root zone composition with position on a sloping area appreciably complicates construction and increases cost of a putting green.
Because the upper portion of the root zone is unsaturated and the ability of the root zone to transmit water drops sharply as it becomes unsaturated (Campbell, 1974), most of the water that is wicked downslope passes through the lower, saturated of the root zone (or nearly saturated portion, depending on the amount of trapped gasses). Given such, a solution to help alleviate dry spots on slopes that would not rely on altering depth or composition of the root zone might be to insert subsurface barriers that run parallel with the contour in the lower portion of the root zone so as to interrupt slopewise capillary connectivity of the root zone. In concept, these capillary barriers would consist of a strip of impermeable metal or plastic sheet such as landscape edging that would extend vertically upward from the top of the drainage material through the saturated bottom portion of the root zone. The saturated portion of the root zone is typically the bottom half of a U.S. Golf Association (USGA)-design green and there would not likely be a net benefit for the capillary barriers to extend much nearer the surface where they might interfere with management practices such as aeration and vertical mowing. The capillary barriers would act in a strictly passive manner to control water storage. The Purr-Wick design of near half a century ago (Daniel, 1978) was developed with some of the same concepts in mind as outlined here for the subsurface capillary barriers, but it involved cumbersome subsurface management of drainage water and therefore was not widely adopted.
The objective of this research was to evaluate the effectiveness of subsurface capillary barriers in controlling the amount of water stored in the root zone profile of a sloping portion of a putting green. We evaluated slopes on greens constructed in line with USGA recommendations (USGA Green Section Staff, 2004) and the Airfield Systems design (Airfield Systems, Oklahoma City, OK). The Airfield Systems-design green was evaluated because the saturated portion of the root zone after irrigation or rainfall is appreciably thicker than it is in the USGA-design green given the same root zone mixture (McInnes and Thomas, 2011).
ASTM 2006. Standard test methods for saturated hydraulic conductivity, water retention, porosity, and bulk density of putting green and sports turf root zones. F1815-06. ASTM International, West Conshohocken, PA.
Bigelow, C.A., Bowman, D.C. & Cassel, D.K. 2004 Physical properties of three sand size classes amended with inorganic materials or sphagnum peat moss for putting green rootzones Crop Sci. 44 900 907
Davis, W.B., Paul, J.L. & Bowman, D. 1990. The sand putting green: Construction and management. Publ. 21448. Univ. of California Div. of Agric. and Nat. Resour., Davis, CA.
Frank, K.W., Leach, B.E., Crum, J.R., Rieke, P.E., Leinauer, B.R., Nikolai, T.A. & Calhoun, R.N. 2005 The effects of a variable depth rootzone on soil moisture in a sloped USGA putting green Intl. Turfgrass Soc. Res. J. 10 1060 1066
Li, D., Minner, D.D. & Christians, N.E. 2008 Managing isolated dry spot by topdressing inorganic amendments on a sloped golf green Acta Hort. 783 341 348
McCoy, E.L. & McCoy, K.R. 2009 Simulation of putting-green soil water dynamics: Implications for turfgrass water use Agr. Water Mgt. 96 405 414
McInnes, K.J. & Thomas, J.C. 2011 Water storage in putting greens constructed with United States Golf Association and Airfield Systems designs Crop Sci. 51 1261 1267
Prettyman, G.W. & McCoy, E.L. 2002 Effect of profile layering, root zone texture, and slope on putting green drainage rates Agron. J. 94 358 364
Prettyman, G.W. & McCoy, E.L. 2003 Profile layering, root zone permeability, and slope affect on soil water content during putting green drainage Crop Sci. 43 985 994
R Development Core Team 2009 R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria.
Ritsema, C.J., Dekker, L.W., van Dam, J. & Oostindie, K. 2004 Principles of flow and transport in turfgrass profiles, and consequences for management Acta Hort. 661 137 144
Simunek, J., Sejna, M. & Genuchten, M.Th. van 1999. The HYDRUS-2D software package for simulating the two-dimensional movement of water, heat, and multiple solutes in variably-saturated media. In: IGWMC-TPS 53,Version 2.0. International Ground Water Modeling Center, Colorado School of Mines, Golden, CO.
Stormont, J.C., Ray, C. & Evans, T.M. 2001 Transmissivity of a nonwoven polypropylene geotextile under suction Geotech. Test J. 24 164 171
Taylor, D.H., Williams, C.F. & Nelson, S.D. 1997 Water retention in root-zone soil mixtures of layered profiles used for sports turf HortScience 32 82 85
van Genuchten, M.T. 1980 A closed-form equation for predicting the hydraulic conductivity of unsaturated soils Soil Sci. Soc. Amer. J. 44 892 898