Abstract
The results of a two-year research aiming to evaluate the effects of corrective treatments on two saline-sodic soils are reported. The trial was carried out in cylindrical pots (high 0.6 m and with a diameter of 0.4 m), provided with a bottom control device to collect drainage water, and located under shed, to avoid rain leaching effect. The two clay soils: Saline and saline-sodic resulting from a four-year experiment in which different crops had been irrigated with 9 solutions obtained by dissolving in distilled water the appropriate amounts of NaCl and CaCl2 by the factorial combination of three salt concentrations and three SAR levels (5, 15 and 45). During the subsequent two-year period, the soils were cropped to barley and borlotto bean and irrigated with freshwater (ECw = 0.5 dS m-1 and SAR = 0.45) whenever the soil contained in the pots lost by evapotranspiration 30% of the maximum available water (MAW). The corrective treatments were carried out by applying CaSO4 to the soils with ESP>6% and leaching fractions equal to 20% of the watering volume to the most saline soils and proportionally lower fractions to the less saline soils, in order to reach, in the drainage water, electrical conductivity (EC) and sodium absorption ratio (SAR) values of 3 dS m-1 and 9, respectively. The reclamation treatments reduced significantly soil salinity and sodicity: Electrical conductivity of the saturation extract (ECe) decreased on average from 12.34 to 3.66 dS m-1; the exchangeable sodium percentage (ESP) dropped by 50.93 and 41.41% respectively for Bologna and Locorotondo soils. Key words: Soil reclamation, gypsum requirement, saline soils, saline-sodic soils.
Highlights
Salinity-induced land degradation is one of the major obstacles to sustainable agricultural production in many arid and semi-arid regions of the world (Bossio et al, 2007)
During the subsequent two-year period, the soils were cropped to barley and borlotto bean and irrigated with freshwater (ECw = 0.5 dS m-1 and sodium absorption ratio (SAR) = 0.45) whenever the soil contained in the pots lost by evapotranspiration 30% of the maximum available water (MAW)
The average values for the soils of Bologna (T1) and Locorotondo (T2) concerning the Electrical conductivity of the saturation extract (ECe), pH and exchangeable sodium percentage (ESP) were respectively 12.25 and 13.61 dS m-1, 7.80 and 7.07 and 6.40% with decreasing values, shifting from the top to the deeper layers, and increasing values with higher salt concentration and SAR of the irrigation water applied in the four previous years
Summary
Salinity-induced land degradation is one of the major obstacles to sustainable agricultural production in many arid and semi-arid regions of the world (Bossio et al, 2007). High salt concentration favours the flocculation of colloids, while a high percentage of exchangeable sodium causes colloids’ dispersion (Hanson et al, 1999; Bauder, 2001; Bauder and Brock, 2001). Another process, somehow reversible, associated with the high percentage of exchangeable sodium is the high expansion of soils (Saskatchewan, 1987; Hanson et., 1999). The most evident physical effect of the increasing level of sodium in the soils is its reduced permeability that is more severe in soils containing montmorillonitic clays than in the soils with illite-vermiculitic clays and kaoliniticsesquioxides (Saskatchewan, 1987)
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