THE EFFECT OF PAPER-MILL WASTE-WATER IRRIGATION AND GYPSUM SOIL AMENDMENTS ON SODIUM ACCUMULATION BY COTTONWOOD AND SOIL

Gypsum soil amendments affected the concentrations of sodium in the st ems and leaves of Populus seedlings irrigated with pulpmill effluent. Concentrations of sodium in the sapling tissues increased with gypsum applications which gave total calcium application rates of 175 mg Ca l (-1) wastewater (ww) and decreased as calcium application rates were i ncreased to 625 mg Ca l(-1) ww, Conversely, stem biomass production de creased as calcium application rates increased to 175 mg Ca l(-1) ww a nd then increased as calcium application increased to 625 mg Ca l(-1) ww. This resulted in no significant differences across treatment in ei ther total sodium uptake or removal of sodium from the soil by the Pop ulus seedlings. Total sodium uptake by Populus was about 0.002% of was tewater inputs. Infiltration rate increased with the increasing gypsum application. Gypsum application rate was not associated with differen ces in the concentration and distribution of sodium in the soil profil e but increased application rates were associated with decreased soil pH.