Applied Soil Ecology 48 (2011) 247–250 Contents lists available at ScienceDirect Applied Soil Ecology journal homepage: www.elsevier.com/locate/apsoil Short communication Microbial application with gypsum increases the saturated hydraulic conductivity of saline–sodic soils Ustun Sahin a,∗ , Sec ¸ kin Ero ˘ glu b , Fikrettin Sahin b a Atatürk University, Faculty of Agriculture, Department of Agricultural Structures and Irrigation, 25240 Erzurum, Turkey b Yeditepe University, Faculty of Engineering and Architecture, Department of Genetics and Bioengineering, 34755 Kayıs ¸da˘ gı, Istanbul, Turkey article info Article history: Received 22 December 2010 Received in revised form 30 March 2011 Accepted 1 April 2011 Keywords: Saturated hydraulic conductivity Microorganisms Remediation Saline–sodic soils abstract Microbial application for the amelioration of sodic and saline–sodic soils may reduce the economic and environmental costs of chemical amendments. The effect of microbial application on saturated hydraulic conductivities of four different saline–sodic soils which were being ameliorated with gypsum was stud- ied. Suspensions of three fungal isolates (Aspergillus spp. FS 9, 11 and Alternaria spp. FS 8) and two bacterial strains (Bacillus subtilis OSU 142 and Bacillus megaterium M3) at 10 4 spore/ml and 10 9 CFU/ml, respectively, were mixed with leaching water and applied to the soil columns. The measured saturated hydraulic conductivities of soil columns after the treatment indicated that saturated hydraulic conduc- tivity of saline–sodic soils increased significantly (P < 0.01) by application of the microorganisms. Average increase for all soils was 68%. The data suggest that microorganisms tested in the present study may have potential to help improve water movement through saline–sodic soils. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Soil degradation resulting from salinity, sodicity, or a combina- tion of both, is a major impediment to optimal utilization of land resources. Salt-affected soils exist mostly under arid and semi-arid climates, in more than 100 countries, and on all the continents except Antarctica (Qadir and Oster, 2002). Currently, at least 20% of the world’s irrigated land is salt-affected. Among those affected by salt, about 60% are sodic (Qadir et al., 2006). Sodic and saline–sodic soils are characterized by reductions in hydraulic conductivity and infiltration rate. These soils consist of large amounts of exchangeable sodium. Soil dispersion is the pri- mary physical process associated with high sodium concentrations. Dispersed clay particles cause plugging of soil pores. This pore plugging impedes water flow and water infiltration into the soil (Warrence et al., 2002). Over the past 100 years, several different site-specific approaches – involving the use of chemical amendments, tillage, crop diversification, water, and electrical currents – have been used to ameliorate sodic and saline–sodic soils. Of these, chemical amendments have been used most extensively (Oster et al., 1999; Qadir and Oster, 2002; Qadir et al., 2006). Chemical amelioration of sodic and saline–sodic soils is driven by providing a source of calcium to replace excess sodium from the ∗ Corresponding author. Tel.: +90 442 231 2619; fax: +90 442 236 0958. E-mail addresses: ussahin@atauni.edu.tr, ussahin@yahoo.com (U. Sahin). cation exchange sites. The replaced sodium is leached from the root zone through excess irrigation, a process that requires adequate flow of water through the soil (Qadir and Oster, 2004; Qadir et al., 2006). Chemical reclamation has become costly for subsistence farm- ers in developing countries. Amendment costs have increased because of greater usage by industry and reductions in government subsidies to farmers (Qadir and Oster, 2002). Gypsum, an eco- nomical alternative for replacing sodium with calcium (Gharaibeh et al., 2009; Oad et al., 2002), has low solubility which can limit its efficiency. In order to provide more active Ca from gypsum amendments and other non-soluble compounds, the possibility of exploiting plants and microorganisms is under investigation. The use of plant metabolites as a strategy to ameliorate saline–sodic soils was reviewed by Qadir et al. (2001), Qadir and Oster (2002) and Qadir et al. (2003). Although some plants were screened for their potential to be used in amelioration, little information is available on the possible effects of microbial-based treatments. Syed et al. (2003) reported successful trials on amelioration of saline–sodic soils where a mixture of different microorganisms was applied to soil without gypsum. Furthermore, experiments conducted with blue–green algae resulted in augmented solubility of gypsum which provided better amelioration for the sodic soils (Subhashini and Kaushik, 1981). In another trial, contrary results to that study were attributed to inability of the transferred bacteria to colonize in the soil (Rao and Burns, 1991). The aim of this work was to study the effect of microbial mix- tures, including fungi and bacteria transferred by leaching water in 0929-1393/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.apsoil.2011.04.001