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Introduction Saline soils are characterised as those containing high levels of soluble salts, mainly sodium chloride (NaCl) and sodium sulphate ([Na.sub.2]S[O.sub.4]) and is one of the world's most serious environmental problems. Estimates on global salinisation in land and water resources have shown that, about 7% of the world's total land area is affected by salt (Ghassemi et al., 1995; Munns et al., 2002). Most of the current and potential agricultural soils where crops are grown are located in low relief landscapes characterised by dense populations, intensive agricultural activities, higher temperatures and evapotranspiration often associated with insufficient leaching leading to greater salt accumulation (Rhoades et al., 1992; De Pascale and Barbieri, 1997). Accumulation of salts in such agricultural soils alters its physico-chemical properties, including pH (Al-Busaidi and Cooksen, 2003), exchangeable sodium ([Na.sub.exch]), electrical conductivity of the saturated paste (E[C.sub.e]), sodium absorption ratio (SAR), exchangeable sodium percentage (ESP), saturated hydraulic conductivity ([K.sub.s]) and soil available water capacity (AWC). Consequently, mineral elements and water availability for plant growth and yield of most crops is affected (Tanji 1990). It has been reported that excessive exchangeable sodium and high pH decrease the soil permeability and infiltration capacity through swelling and dispersion of clays as well as slaking of aggregates (Lauchli and Epstein, 1990). These modifications may further compromise the yield of salinised crops, thus, jeopardising the income of most farmers. Some studies have shown that the use of gypsum on saline-sodic and sodic soils improves most of the properties including the infiltration rate and helps in leaching the salts into the lower layers (Qureshi and Barrett-Lennard, 1998). For example, it has been shown that maximum improvement in hydraulic conductivity (Ks) was only possible with simulated sub-soiling and gypsum-saturated solution (Shahid, 1993). Although abundant literature on the effect of gypsum on sodic and saline-sodic is available (Qadir et al., 2001; Sahin et al., 2003; Makoi and Ndakidemi, 2007), only few studies have reported the effects of gypsum and placement methods on saline soils (Rains and Goyal, 2003). So, understanding the effect of gypsum and placement methods on these properties may be of critical importance in order to optimise farm management strategies by farmers practicing agricultural activities in such soils. The objective of this study was to therefore assess the effect of gypsum and placement methods on [Na.sub.exch], E[C.sub.e], SAR, ESP, Ks and AW in a saline loamy sand soil.

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December 15
Southern Cross Publisher
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