Recently, urea–formaldehyde resin foam (UFRF) has been introduced as a synthetic organic soil amendment and is used as a substrate in the propagation and growth of plants in hydroponic systems, soilless cultures, and substrates used in production of container-grown plants, in roof gardens, and sports fields. Urea–formaldehyde resin foam and its effect on plant growth has been the subject of study as an amendment for soils and organic substrates for several researchers (Chan and Joyce, 2007; Mooney and Baker, 1999; Nektarios et al., 2003, 2004; Nguyen et al., 2009; Nikolopoulou and Nektarios, 2004; Nikolopoulou et al., 2004). Urea–formaldehyde resin foam is environmentally friendly, lightweight (18–30 kg·m−3), slowly biodegradable over a period of 20 years, sterile, and has a high water retention capacity (57% v/v) (Werminghausen, 1972). Furthermore, UFRF has been found to increase air-filled porosity and water infiltration of fine texture soils and water retention of coarse texture soils (Baader, 1999). In this article, a UFRF with the brand name Fytocell was studied (Fig. 1). Over the past 10-year introduction period, Fytocell has provided such results that could characterize it as a “unique and promising” substrate for the soilless culture sector (Welleman, 2005). This compound has a spongy structure and could be used either in the form of slabs or flakes as a component of organic and inorganic mixtures.
Previous research using UFRF has mainly focused on the study of the physical properties of UFRF-amended soils and organic substrates (Chan and Joyce, 2007; Mooney and Baker, 1999; Nektarios et al., 2003, 2004; Nguyen et al., 2009). Mooney and Baker (1999) determined the Ks of UFRF-amended sandy soils and Nektarios et al. (2003, 2004) determined the θ(h) of UFRF-amended soils and substrates.
However, the knowledge of both main hydraulic properties of UFRF-amended substrates such as θ(h) and the relationship between unsaturated hydraulic conductivity and volumetric water content, K(θ), is necessary for the selection of substrates for plant growth and the proper management of irrigation. Although θ(h) for substrates is easily determined in the laboratory, the direct experimental determination of K(θ) is usually difficult, time-consuming, and requires specialized laboratory equipment (Londra, 2010). Many researchers have used mathematical models to calculate θ(h) and K(θ) for substrates (Fonteno et al., 1981; Karlovich and Fonteno, 1986; Londra, 2001; Londra and Valiantzas, 2011; Milks et al., 1989; Valiantzas et al., 2007; Wallach et al., 1992). However, large fluctuations in hydraulic conductivity (K) between different substrates limit the predictive value of these models.
An indirect experimental procedure for estimating K(θ) is the one-step outflow method. This procedure is one of the most widely used laboratory methods for determining K(θ) (if water retention data are available) and the soil water diffusivity, D, as a function of the volumetric water content θ [D(θ)] on porous material samples of small height. In the one-step outflow method, a short soil or substrate sample of height L, with initial water content θi, is suddenly subjected to a large increment of pressure and the outflow volume, V, is recorded with time, t, until the water content reaches the final equilibrium value θf (Gardner, 1962; Gupta et al., 1974; Passioura, 1976; Valiantzas, 1989; Valiantzas et al., 1988, 2007).
Compared with other methods, the one-step outflow method requires little time for the calculation of K but cannot be applied in the first outflow stage, in which the flow is practically determined by the resistance of the porous plate (Passioura, 1976; Valiantzas, 1990). Therefore, the method cannot be used for the calculation of K near saturation.
In this study, laboratory experiments were conducted for determining the θ(h) in substrate samples of Fytocell, loam soil/Fytocell (60/40 v/v), coir/Fytocell (60/40 v/v), coir, and loam soil. In the same substrate samples under the same experimental apparatus, one-step outflow experiments were also carried out to estimate the relations of D(θ) and consequently K(θ). Therefore, the K(θ) values were compared with the values predicted by the most popular closed-form analytical hydraulic model of van Genuchten–Mualem. Furthermore, the Ks was determined experimentally.
The main aim of this study was to evaluate the effect of UFRF on the hydraulic behavior of its mixtures with a soil and an organic substrate. Contrary to previously reported research (Chan and Joyce, 2007; Mooney and Baker, 1999; Nektarios et al., 2003, 2004; Nguyen et al., 2009), in this study, both basic hydraulic properties, the water retention curve and the relationship between unsaturated hydraulic conductivity and volumetric water content, of the UFRF and its mixtures were determined using a fast and easy methodology in the same substrate sample for a range of water contents of vital importance for the plant growth.
BaaderP.1999Fytogreen-foam in laying out sport fields. 1st Fytogreen Seminar 2–3 Dec. Beneden Leeuwen The Netherlands
ChanC.L.JoyceD.C.2007Effects of urea formaldehyde resin foam soil amendment on growth and response to transient water deficit stress of potted Flindersia schottiana saplingsSci. Hort.114112120
FontenoW.C.CasselD.K.LarsonR.A.1981Physical properties of three container media and their effect on Poinsettia growthJ. Amer. Soc. Hort. Sci.106736741
GuptaS.C.FarrelD.A.LarsonW.E.1974Determining effective soil water diffusivities from one-step outflow experimentsSoil Sci. Soc. Amer. J.38710716
HainesW.B.1930Studies in the physical properties of soils. V. The hysteresis effect in capillary properties and the modes of moisture distribution associated therewithJ. Agr. Sci.2097116
KarlovichP.T.FontenoW.C.1986The effect of soil moisture tension and volume moisture on the growth of chrysanthemum in three container mediaJ. Amer. Soc. Hort. Sci.111191195
KluteA.DirksenC.1986Hydraulic conductivity and diffusivity: Laboratory methods p. 687–734. In: Klute A. (ed.). Methods of soil analysis: Part 1 physical and mineralogical methods. American Society of Agronomy Madison WI
LondraP.A.2001Moisture–aeration balance of substrates as developed under different irrigation treatments. PhD thesis Agricultural University of Athens Dept. of Natural Resources Management and Agricultural Engineering Athens Greece
LondraP.A.2010Simultaneous determination of water retention curve and unsaturated hydraulic conductivity of substrates using a steady-state laboratory methodHortScience4511061112
MilksR.R.FontenoW.C.LarsonR.1989Hydrology of horticultural substrates: I. Mathematical models for moisture characteristics of horticultural container mediaJ. Amer. Soc. Hort. Sci.1444852
MooneyS.BakerS.1999The effects of fytogreen foam on the soil physical properties of sand-dominated root zones for sports turf: A laboratory study. Document No. 0066/3. The Sports Turf Research Institute (STRI). p. 17
NektariosP.A.NikolopoulouA.E.ChronopoulosI.2004Sod establishment and turfgrass growth as affected by urea–formaldehyde resin foam soil amendmentSci. Hort.100203213
NektariosP.A.TsiotsiopoulouP.ChronopoulosI.2003Soil amendments reduce roof garden weight and influence the growth rate of LantanaHortScience38618622
NguyenT.-T.JoyceD.C.DinhS.-Q.2009Effects of artificial amendments in potting media on Orthosiphon aristatus growth and developmentSci. Hort.123129136
NikolopoulouA.E.NektariosP.A.2004Effects of resin foam soil amendment on the growth of turfgrass subjected to different compaction levelsActa Hort.661177181
NikolopoulouA.E.TsoggarakisG.GourliasD.NektariosP.A.2004Effects of fertilisers and foam soil amendment on sod establishmentActa Hort.661265270
ValiantzasJ.D.1989A simple approximate equation to calculate diffusivities from one-step outflow experimentsSoil Sci. Soc. Amer. J.53342349
ValiantzasJ.D.KerkidesP.G.PoulovassilisA.1988An improvement to the one-step outflow method for the determination of soil water diffusivitiesWater Resour. Res.2419111920
ValiantzasJ.D.LondraP.A.SassalouA.2007Explicit formulae for the soil water diffusivity using the one-step outflow techniqueSoil Sci. Soc. Amer. J.7116851693
ValiantzasJ.D.SassalouA.1991Laboratory determination of unsaturated hydraulic conductivity using a generalized-form hydraulic modelJ. Hydrol.128293304
WallachR.da SilvaF.F.ChenY.1992Unsaturated hydraulic characteristics of composted agricultural wastes, tuff and their mixturesSoil Sci.153434441
WerminghausenB.1972The application of synthetic media in plant propagation. III Symposium on Peat in Horticulture, Dublin IrelandActa Hort.26159164