325 Arid Land Research and Management, 28:325–339, 2014 Copyright © Taylor & Francis Group, LLC ISSN: 1532-4982 print/1532-4990 online DOI: 10.1080/15324982.2013.856357 Effect of Soil Conditioners on Cation Ratio of Soil Structural Stability, Structural Stability Indicators in a Sodic Soil, and On Dry Weight of Maize Hojat Emami, Ali Reza Astaraei, Amir Fotovat, and Mojtaba Khotabaei Ferdowsi University of Mashhad, Mashhad, Iran The relative effects of Na + and K + on soil structural stability due to application of some conditioners in sodic soils are not clearly defined by the existing literature. In this research, a completely randomized design experiment was performed to quan- tify the effect of some conditioners on physical properties in a loamy sodic soil. Five treatments included no conditioner as a control, urban solid waste compost (MC), Vermi-compose (VC), poultry manure (PM), and gypsum powder (G). The amount of each soil amendment was 10 ton/ha and each treatment consisted of 3 replica- tions. The most important structural stability indicators including air capacity (AC), water dispersible clay (WDC), the slope of the retention curve at the inflection point (S gi index), and mean weight diameter of aggregates (MWD) were measured. The results showed that compared with the control, soil conditioners improved soil struc- tural stability indicators significantly (P < 0.05). Due to application of studied con- ditioners, the values of AC, WDC, S gi index, and MWD increased. In addition, it was demonstrated that there was a negative and significant correlation between CROSS and SAR and structural stability indicators. By increasing SAR and Cation Ratio of Soil Structural Stability WDC, S gi index, AC, and MWD values were decreased and as a result of these processes and improvement the physical condition of seedbeds, the dry weight of maize was increased. Keywords conditioners, CROSS, maize, SAR, sodicity, structural stability Soil aggregates are formed by combining clay, silt and sand particles through various ions and organic compounds. Cultivated soils in arid and semi arid regions particu- larly in Iran are generally low in organic matter. In soils with low organic matter, clay particles are bound to each other through cationic bonds (Imanparast et al., 2012). The stability of soil aggregates depends on the nature of interaction between water molecules and soil particles. Clay to clay bonding is mediated by exchangeable cations such as potassium, magnesium, and calcium. Because of negative charge of clay par- ticles and positive charge of cations, they attract each other and form different types of bonding (Rengasamy & Marchuk, 2011). Soil degradation resulting from salinity and/or sodicity is a major environmen- tal concern with severe adverse impacts on agricultural productivity and sustain- ability, especially in arid and semiarid climates (Suarez, 2001; Qadir et al., 2008). Received 16 July 2013; accepted 14 October 2013. Address correspondence to Hojat Emami, Ferdowsi University of Mashhad, Mashhad, Iran. E-mail: hemami@um.ac.ir Downloaded by [46.143.214.22] at 00:58 19 March 2014