Evaluation of the effects of incorporation rate and depth of water-retentive amendment materials in sports turf constructions

The objective of the current laboratory study was to assess the effects of a number of amendment materials and the depth of incorporation on water retention. 300 mm rootzone profiles were established in 150 mm diameter plastic cylinders over a 50 mm gravel drainage layer. Five amendment materials (sphagnum peat, compost, zeolite, TerraCottem and Stockosorb) were mixed with a medium-coarse sand at various rates. The upper rootzone layer (0–150 mm) included 50%, 100% and 150% of published or manufacturersã recommended rates of each amendment material. Three amendment rates were included in the lower rootzone layer (150–300 mm): pure sand, half the amendment rate of the top layer, and the same amendment rate as the top layer. The following measurements were made: water retention in individual layers, volumetric water content in the top layer (0–60 mm), shear strength, surface hardness, permanent wilting point. Water retention was significantly influenced by the different amendment materials. The most water retentive mixes were those containing peat and Stockosorb, whilst the least retentive contained the TerraCottem and the pure sand. The influence of amendment rate in the lower layer was less in comparison with the top layer. The incorporation of amendment materials in the lower rootzone had no significant effect on water retention in the upper rootzone but did increase the total water storage in the profile and this would have some implications for plant growth during drier periods.Rootzone mixes containing peat and compost had the highest shear strength whilst the Stockosorb gave the lowest strength because the expansion of the polymer reduced rootzone density and therefore the degree of contact between the sand particles. The hardest surface was measured when zeolite was used and the softest surfaces resulted from the use of Stockosorb.