Effects of consecutive applications of gypsum in equal, increasing, and decreasing quantities on soil hydraulic conductivity of a saline-sodic soil Ustun Sahin 1 *, Taskin Oztas 2 , and Omer Anapali 1 1 Ataturk University, Faculty of Agriculture, Dept. of Agric.Structures and Irrigation, 25240, Erzurum, Turkey 2 Ataturk University, Faculty of Agriculture, Dept. of Soil Science, 25240, Erzurum, Turkey Accepted5July2003 Summary ± Zusammenfassung The objective of this study was to determine the effects of consecutive application of gypsum dissolved in leaching water on hydraulic conduc- tivity of a saline-sodic soil. Drainage type plastic columns with a 10cm diameter were used in this laboratory experiment. Soil depth within columns was 30cm with an average bulk density of 1.38 gcm ±3 . Leaching water was applied in six equal portions. Total gypsum was applied at 1, 3, and 5 portions after dissolving in leaching water. In dissolution, equal (1.273 + 1.273 + 1.273 Mg ha ±1 ), increasing (0.637 + 1.273 + 1.910Mgha ±1 )anddecreasing(1.910+1.273+0.637Mgha ±1 )quantitiesofgypsumwereused.Resultswerecomparedwiththecontroltreat- ment, in which total amount of gypsum were mixed with surface layer of soil column before leaching. Hydraulic conductivity of soil increased in alltreatments.Themaximumhydraulicconductivityvaluewasobtainedatconsecutiveapplicationofgypsumatdecreasingquantities. Einfluss konsekutiver Gipsapplikation in gleichen, zunehmenden und abnehmenden Mengen auf die hydraulische Leitfähigkeit eines natriumversalzten Bodens Ziel dieser Arbeit war es, den Einfluss einer konsekutiven Applikation von in Sickerwasser gelöstem Gips auf die hydraulische Leitfähigkeit eines natriumversalzten Bodens zu untersuchen. Die Versuche wurden in Plastiksäulen mit einem Durchmesser von 10cm mit 30cm Boden- tiefe in den Säulen bei einer durchschnittlichen Rohdichte von 1.38 gcm ±3 durchgeführt. Das Sickerwasser wurde in sechs gleichen Teilen zugeführt. Der gesamte Gips wurde nach Auflösung in 1, 3 und 5 Portionen zugeführt. In Lösung wurden gleiche (1.273 + 1.273 + 1.273 Mg ha ±1 ),zunehmende(0.637+1.273+1.910Mgha ±1 )undabnehmende(1.910+1.273+0.637Mgha ±1 ) Mengen an Gips appliziert. Die Ergeb- nisse wurden mit der Kontrolle verglichen, bei der der gesamte Gips vor dem Perkolationsversuch in die oberflächennahe Bodenschicht einge- mischt wurde. Die hydraulische Leitfähigkeit des Bodens nahm bei allen Behandlungen zu. Der höchste Wert wurde bei der konsekutiven ApplikationvonGipsmitabnehmendenMengenerreicht. Key words: hydraulic conductivity / saline-sodic soil / gypsum / intermittent ponding PNSSP111/5B 1 Introduction The primary limitation to reclamation of saline-sodic soils is the low hydraulic conductivity rather than the initial salt con- tent or depth of leaching water required (Harker and Mikal- son, 1990). The hydraulic conductivity of soils decreases with an increase in the proportion of exchangeable soil Na and a decrease in the total electrolyte concentration of the soil solu- tion (Quirk and Schofield, 1955). The main mechanisms for the reduced hydraulic conductivity are the swelling of smecti- tes in clayey soils, and dispersion and movement of clay par- ticles resulting in pore blockage in coarser soils, especially whenleachedwithlowelectrolytewater(Minhas etal.,1999). Saline-sodic soils can be reclaimed by providing a source of Ca 2+ , such as gypsum, to replace Na + from the colloid¢s cation exchange sites, a process that requires the flow of water through the soil (Oster and Frenkel, 1980; Ilyas et al., 1993). Due to its solubility, low cost, and availability, gypsum is the most common of the chemical amendments used for increasing permeability (Oster , 1982; Keren, 1996). The macroporosity of soils is stabilized by treatment with gypsum, and the concentration of Ca electrolyte maintained in the soil solution prevents the disruption of aggregates and the occlu- sion of pores by dispersed clay particles (Greene et al., 1988). The gypsum may be applied to soil by one of three ways, (1) dissolving in leaching water, (2) incorporating into soil or (3) spreading over soil surface (Ayers and Westcot, 1985; Simu- nek and Suarez, 1997; Oster et al., 1999). The depth of mixing had no effect on gypsum dissolution (Gupta et al., 1985). Oster (1982) reported the effect of depth of mixing on gypsum dissolution was small. The application of gypsum as dissolved in leaching water is more effective than spreading over the land in terms of reducing reclamation costs (Kemper et al., 1975). The long-term electrolyte effect of gypsum is very important for high hydraulic conductivity (Shainberg et al., 1982). If electrolyte concentration of the percolating solu- tion is adequate to reduce clay swelling, the permeability of the soil remains high (Abu-Sharar et al., 1987; Keren, 1996; Quirk, 2001). Gypsum application to leaching water requires less gypsum as compared with application of granulated gyp- sum to soil because of loss of gypsum into the cracks over soil surface. The efficiency of gypsum applied to leaching water increases if the electrical conductivity of leaching water islessthan0.5dSm ±1 (Munsuz etal.,2001).Itwasstatedby Mumsuz et al. (2001) that the efficiency of gypsum would be low in water with high salt content since the difficulty of Ca application to soil in order to eliminate Na efficiency in soil solution. ã 2003WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim 1436-8730/03/0510-621 * Correspondence: Prof. Dr. U. Sahin; E-mail: ussahin@yahoo.com J. Plant Nutr. Soil Sci. 2003, 166, 621±624 DOI: 10.1002/jpln.200321115 621