UPTAKE OF SHALLOW GROUNDWATER BY COTTON - GROWTH STAGE, GROUNDWATER SALINITY EFFECTS IN COLUMN LYSIMETERS

A 3-year column lysimeter experiment was conducted with cotton (Gossyp ium hirsutum L.) to determine the influence of shallow groundwater sal inity on groundwater uptake. Nonsaline (0.3 dS m(-1)) irrigation water was applied at 7-day intervals throughout the growing season, with th e cotton allowed to use stored soil water and groundwater as root wate r uptake permitted. Groundwater salinities ranging from 0.3 dS m(-1) e lectrical conductivity (EC(w)) to 30.8 dS m(-1) were evaluated. Water for leaching was applied following harvest each year in amounts adequa te to produce a nonsaline soil profile at the beginning of each year. Equations were developed to describe relationships between day of year , growth stage or growing degree days and shallow groundwater uptake. Groundwater contributed about 30 to 42% of seasonal total evapotranspi ration (ET) in treatments with groundwater salinity less than or equal to 20 dS m(-1) but declined to 12 to 19% of total ET at higher salini ty levels.