Studying some hydro-physical properties of two soils amended with kaolinite-modified cross-linked poly-acrylamides Rashad A. Hussien a, ⁎, Ahmed M. Donia b , Asem A. Atia b , Osama F. El-Sedfy a , Azza R. Abd El-Hamid a , Rama T. Rashad a, ⁎ a Soil, Water and Environment Research Institute, Agricultural Research Center, Giza, Egypt b Department of Chemistry, Faculty of Science, Menoufia University, Menoufia, Egypt abstract article info Article history: Received 28 April 2011 Received in revised form 20 December 2011 Accepted 22 December 2011 Available online xxxx Keywords: Swelling degree Hydro-physical properties Pore size distribution Hydraulic conductivity Sandy soil Cross-linked hydrogel A poly[(acrylic acid)-co-acrylamide] hydrogel was prepared in the laboratory through polymerization of par- tially neutralized acrylic acid (AA) in the presence of N,N′-methylene bisacrylamide (MBA) as a crosslinker. The polymer was prepared without an additive (H1) or with 5% (w/w) kaolinite clay mineral added during the polymerization (H2). The swelling of the hydrogel in distilled water as well as within the soil matrix was studied. Some hydro-physical properties of two different soil samples amended with the hydrogel were also studied. The S1 soil was sandy and non-saline; and the S2 soil was sandy clay loam and slightly sa- line. The swelling degrees (S) in distilled water were 97.8 and 282.8 g/g of the hydrogel dried at 70 °C, for the non-modified H1 and kaolinite-modified H2 hydrogels, respectively. The S values of H1 and H2 hydrogels, within the S1 soil were 85.45 and 81.25 g/g, respectively. While within the S2 soil, the S values of H1 and H2 hydrogels were 31.17 and 16.32 g/g, respectively. The change in the studied hydro-physical properties of soil treated by the hydrogel was more dependent on the soil texture and salinity and the hydrogel concen- tration in soil than on the swelling degree of the hydrogel. The change in the bulk density values of the soil– hydrogel mixture was in the range 90.1%–71.43% relative to the soil sample free of hydrogel. While the change in the total porosity values were in the range of 98.83%–132.64%. The effect of presence of the hydro- gel on the hydraulic conductivity of the soil samples was discussed. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Reclamation and land utilization of the desert areas, often sandy, are faced by several difficulties (Abed et al., 1981 and El-Hady et al., 1990). To a large degree, the soil quality depends on the size, shape and arrange- ment of solids and voids (Abdel-Mawgoud et al., 2006; Abd El-Hamid, 2004). In the arid and semiarid regions, water availability is often the lim- iting factor determining the size of cultivated area (El-Hady et al., 2006). High sodium in sodic soils or CaCO 3 content in some soils causes some difficulties such as reduced infiltration and poor drainage. Also, it causes the crop damage due to standing water or inadequate aeration in the root zoon and in alga growth on the soil surface (Abu-Hamdeh, 2004). Both linear and cross-linked polymers have been widely used as soil conditioners for different application purposes (Anagnostopoulos, 2005; Hayat and Ali, 2004; Orts et al., 2000). Some commercially avail- able conditioners were used in many studies (Ajwa and Trouts, 2006; Bhat et al., 2006). Two types of polymeric soil conditioners are known: (i) cross-linked polymers (hydrogels) that are used to improve the water holding capacity of the soil and (ii) linear polymers that are used to for stabilizing the soil aggregates and structure in order to min- imize crust formation, runoff and soil erosion. They may change the mean diameter of the soil pores which sometimes enhances water transmitting properties (Bhardwaj and Mclaughlin, 2007; Bhat et al., 2009; Jhurry, 1997; Tayel and El-Hady, 1981). Poly-acrylamide (PAM) is a synthetic polymer that degrades in the soil environment at rates less than 10% per year (Orts et al., 2000). Hydrogels are loosely cross-linked, highly hydrophilic, organic polymers. They can absorb and retain aqueous fluids up to 500 times of their own weight (Guilherme et al., 2005; Li et al., 2005). In the field application, such absorbents exhibited a limited swelling ca- pacity within the soil matrix. Their swelling efficiencies decrease with increasing the water salinity (Akhter et al., 2004; Kazanskii and Dubrovisky, 1992). Free swelling of some hydrogel polymers was in the range 200–500 g/g of the polymer, but when mixed with the sandy soil it was 40–140 g/g. Mixing the suitable hydrogel with the organic material applied to soil (natural soil conditioners like organic manures and composts) is sometimes more effective and economic than using each of them alone (El-Hady and Abo-Sedera, 2006; El- Hady and Camilia, 2006). The yield, uptake of nutrients and both water and fertilizers use efficiency may decrease by the use of a con- centration higher than the critical (over dose) of the applied hydrogel (El-Hady and Camilia, 2006). Better understanding of the interaction Catena 92 (2012) 172–178 ⁎ Corresponding authors. Tel.: + 20 106 2856224. E-mail address: rtalat2005@yahoo.com (R.A. Hussien). 0341-8162/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.catena.2011.12.010 Contents lists available at SciVerse ScienceDirect Catena journal homepage: www.elsevier.com/locate/catena