The effect of soil texture and organic amendment on the hydrological behaviour of coarse-textured soils J. G. Wesseling 1 , C. R. S toof 2 , C. J. R itsema 1,2 , K. O ostindie 1 & L. W. D ekker 1 1 Wageningen University and Research Center, Alterra, Soil Science Center, P.O. Box 47, 6700 AA Wageningen, The Netherlands, and 2 Wageningen University and Research Center, Land Degradation and Development Group, P.O. Box 47, 6700 AA Wageningen, The Netherlands Abstract To gain more insight into the hydrological behaviour of coarse-textured soils, the physical properties of artificially created soil mixtures with different texture were determined. The mixtures were prepared according to the specifications of the United States Golf Association (USGA) for constructing putting greens. In addition, the effect of 10 vol.% organic matter addition was studied. The soil moisture reten- tion and hydraulic conductivity relationships of the different mixtures were determined and their hydro- logical behaviour was studied using the numerical model SoWaM. Both texture and organic matter addition substantially affected the hydraulic properties. Hydraulic conductivity significantly increased with increasing coarseness while moisture retention decreased. On the other hand, organic matter addi- tion reduced saturated hydraulic conductivity by a factor of 10 to 100 and distinctly increased moisture retention capacity. The amounts of total available water were increased by the addition of organic matter between 144% (slightly coarse texture) and 434% (very coarse texture). Results indicate that the mixtures can contain only 2–16% plant available water and therefore need frequent irrigation to maintain plant growth. Addition of organic matter seems a good solution to reduce the irrigation water requirements but it increases the risk of ponding or runoff because of large reductions in the saturated hydraulic conductivity sometimes to below the rate of 3.6 m ⁄ day recommended by the USGA. Keywords: Soil physics, texture, irrigation, model simulation, coarse sand, SoWaM, sports turfs, moisture characteristics Introduction In previous papers, we presented an universal way to describe the physical properties of a soil by means of a fitting proced- ure using cubical splines (Wesseling et al., 2008), emphasized the risks of clustering soil samples into soil physical classes (Wesseling, 2009a) and introduced a new and flexible com- puter programme to simulate one-dimensional moisture flow (Wesseling et al., 2009b). While developing and testing these methods and tools, the soil physical properties of a wide range of soils were required. Both raw data of soil physical relationships, averaged characteristics and more generic pedo- transfer functions can be found in different databases, like the Staring Series (Wo¨sten, 1987; Wo¨sten et al., 2001), the UNSODA database (Nemes et al., 2001), the Hypres data- base (Wo¨sten et al., 1998; see http://www.macaulay.ac.uk/ hypres/) and the Priapus database (Stolte et al., 2007). Searching these databases and the scientific literature yielded little data on the soil physical properties of coarse-textured soils. A quick literature search showed that these soils have been investigated in combination with transport of NO 3 ) (Dodd et al., 2000), microbiology (Kieft et al., 1995), gas dif- fusion (Jones et al., 2003), the amendment of fly ash (Adriano & Weber, 2001), waste water (Harrison et al., 2000) and earthworms (Zhang & Schrader, 1993), but very few measure- ments had been performed on the soil physical properties of coarse-textured materials. This is surprising, the more so when one realizes that 3.5% of the Dutch topsoils have a median particle size of 210 lm or higher (the Dutch definition of coarse sand, see e.g. Brouwer et al., 1996). Coarse soil materials usually have limited possibilities for agricultural production due to their poor fertility and low water holding capacity, often causing a large irrigation demand. Despite Correspondence: J. G. Wesseling. E-mail: jan.wesseling@wur.nl Received November 2008; accepted after revision May 2009 Soil Use and Management, September 2009, 25, 274–283 doi: 10.1111/j.1475-2743.2009.00224.x 274 ª 2009 The Authors. Journal compilation ª 2009 British Society of Soil Science Soil Use and Management