Use of Volcanic Mulch to Rehabilitate Saline‐Sodic Soils

Abstract

Natural soil salinization and sodication processes that restrict or prevent crop growth are commonplace in arid regions. In saline‐sodic soils of arid parts of the Canarian archipelago, where annual rainfall is <150 mm, a traditional agriculture system has been developed using basaltic tephra mulch. This system has enabled dry crop farming to take place even under the most adverse of natural conditions. The present work compares the salinity‐sodicity in the cultivated layer of soils that were covered with 10 to 15 cm of tephra mulch as recently as 20 yr ago with that of adjacent unmulched soils. These soils have never been irrigated. Results show significant differences in electrical conductivity (EC) and exchangeable Na percentage (ESP). The natural, unmulched soils are extremely saline‐sodic (ECse 43 dSm−1, ESP 44), whereas the mulched soils are neither saline nor sodic (ECse 1.5 dSm−1, ESP 9). The reduction in salinity and sodicity in the mulched soils was related to the change in soil moisture regime caused by the mulch covering, which increases infiltration and reduces evaporation and upward movement of Na+ and other salts. Probably, additional water from dew could also contribute. The greater dilution of soil solution through increased soil water content, increased Na+ leaching and the dissolution of calcium salts may account for the desalinization and desodication. These results were confirmed through monitoring of a soil from the moment it was originally covered with tephra. They also revealed salt leaching process is a short‐term. Tephra mulching can, therefore, be a highly efficient technique for the recovery of saline‐sodic soils under dry farming conditions.