Salinization and sodication in a cracking clay soil during bypass flow [Sicily]
2005
Crescimanno, G. | Santis, A. De
Six outflow experiments with NaCl-CaCl sub(2) solutions were performed in a cracking clay soil by inducing bypass flow processes similar to those occurring in the field when saline/sodic waters are supplied by irrigation systems involving high application rates. Three solutions with Sodium Adsorption Ratio, SAR, progressively higher than the initial Exchangeable Sodium Percentage, ESP, and high cationic concentration, C, were alternated to three solutions having same values of SAR but lower C, in order to explore: the process of Na-Ca exchange and subsequent sodication during bypass flow; the effect of alternating waters with different C in the process of salt-leaching occurring under bypass flow conditions, at increasing SAR-ESP. The results of the outflow experiments showed that Na-Ca exchange occurred during bypass flow, determining Na adsorption and accumulation in the exchange phase. An increase of about 100% in the soil ESP was measured at the end of the six outflow experiments in the top layer (8-10 cm). Being the volume of the supplied saline/sodic solutions very small compared to the pore volume, this result indicates that a considerable risk of sodication may occur under bypass flow conditions. In addition, the experiments performed indicated that, in a cracking soil, alternating a low salinity solution to a high saline water is a management practice preventing accumulation of solutes when solutions with SAR close to the soil ESP are used. Instead, when solutions with SAR higher than the initial soil ESP are progressively supplied, due to the Na-Ca exchange with subsequent sodication, the efficiency of salt-leaching decreases at increasing SAR-ESP. With reference to management of irrigation, these results indicate that when a progressive increase in the soil ESP is induced by use or re-use of saline/sodic waters, application of waters having not only lower C but also lower SAR is necessary to prevent salinization and sodication
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