Water retention in root-zone soil mixtures of layered profiles used for sports turf

Where coarse-textured materials, such as gravel, underlie the root-zone layer of sports turf soil profiles, mater retention in the root-zone layer is increased. The objective of this research was to determine the water retention characteristics in sand and sand : peat mixtures placed over coarse-textured layers and to determine how sand particle size and type of peat in the mixtures influenced water distribution after drainage. Soil profiles consisted of 30 cm of sand or sand : peat mixtures over 5 cm of predominantly coarse and very coarse sand, which in turn was over 10 cm of gravel. Excess water was added to the profile and allowed to drain for 24 or 48 h, following which water content and air-filled porosity (AFP) in the mixtures were evaluated. Regardless of the root-zone mixture, the coarse-textured sublayers resulted in a wet zone in the lower portion of the root-zone mixture. An unamended, predominantly medium and coarse sand, when used in the 30-cm root-zone layer, maintained approximate to 10% AFP in the lower 6 cm after drainage. Sand : peat mixtures using this sand generally maintained 3% to 8% AFP in the lower 12 cm of the root-zone layer. An unamended, predominantly fine and medium sand root-zone layer had approximate to 6% AFP in the lower 9 cm and sand : peat mixtures using this sand had <5% AFP in the lower 12 to 18 cm of the root-zone layer, with significant portions remaining at or near saturation after 24 or 48 h of drainage.