SHOOT GROWTH, PLANT-TISSUE ELEMENTAL COMPOSITION, AND SOIL-SALINITY FOLLOWING IRRIGATION OF ALFALFA AND TALL FESCUE WITH HIGH-SULFATE WATERS

Groundwater contaminated with sulfate (SO42-) at concentrations higher than allowable for drinking water might still be usable for irrigatio n. Objectives were to determine the growth response and mineral uptake of two forage crops irrigated with waters containing SO42- at concent rations ranging from 175 to 1743 mg/L, and with electrical conductivit ies (EC) ranging from 1.2 to 3.6 dS/m. Plants were grown for 12 weeks in 8-L pots containing a calcareous sandy loam and were harvested at 4 , 8, or 12 weeks for plant growth measurements and tissue analysis. Di gested leaves, stems, and reproductive tissues were analyzed by induct ively coupled plasma (ICP) spectroscopy at each harvest, as were satur ated soil paste extracts. Shoot growth of tall fescue (Festuca arundin acea Schreb.) was not affected by irrigation water treatment, whereas shoot growth of alfalfa (Medicago sativa L.) was increased by a modera te level of soil solution SO42-. Sulfur (S), boron (B), magnesium (Mg) , sodium (Na), and zinc (Zn) concentrations in shoot tissues of both s pecies showed a tendency to increase with increasing SO42- content of irrigation water. Shoot tissue concentration of molybdenum (Mo) increa sed with maturation in both species, while the concentrations of B, po tassium (K), manganese (Mn), Na, and Zn decreased. Soil saturated past e extract concentrations of Mg and Na increased with irrigation water Mg and Na concentrations, while Ca and S concentrations in the soil so lution became saturated at the higher irrigation water concentrations of these elements.