SALT REMOVAL IN A SALINE SOIL USING FALL IRRIGATION UNDER SUBSURFACE GRID DRAINAGE

A study was initiated during 1987 and 1988 to evaluate the effectivene ss of grid drainage and fall irrigation in reclaiming an area affected by severe salinity due to canal seepage. Three test plots were establ ished for the study: highly saline, standard pivot irrigation (plot 1) ; highly saline, standard pivot irrigation plus additional solid set f all irrigation (plot 2); and moderately saline, standard pivot irrigat ion (plot 3). Subsurface grid drainage, with a mean drain depth of 1.4 m, was present at all three plots located along the main canal of the St. Mary River Irrigation District in southern Alberta, Canada. Water levels, drain outflow, electrical conductivity (EC(e)), and sodium ad sorption ratio (SAR(e)) of the saturation paste extract were determine d. Under conventional center pivot irrigation, no significant reductio n in EC(e) or SAR(e) was achieved over the 14 mo period. When addition al fall irrigation (374 mm) was applied, with a solid set sprinkler sy stem, a significant reduction in EC(e) of 32% and SAR(e) of 27% was ob served in the upper 0.15 m of soil. Similarly, EC(e) and SAR(e) of the upper 0.30 m of soil decreased by 18% and 13%, respectively. Signific ant resalinization of the upper 0.30 m of soil occurred over winter in all plots. Results demonstrated the ability of fall irrigation to lea ch salts from the top 0.30 m during a period of low consumptive use, w hich could lead to reclamation. Long term monitoring would be required to determine whether a further and permanent decline in salinity coul d be achieved.