Establishment and production of lucerne on a salinised clay soil irrigated with moderately saline groundwater

Abstract

Groundwater (ECw 3.8 dS/m, and a sodium adsorption ratio of 15.0) pumped from a shallow aquifer was used to irrigate a lucerne crop established in a salinised clay soil after initial leaching of salts. Pumping and irrigation with groundwater reduced the topsoil salinity (ECe) from 22.1 to 5.9 dS/m in the first 15 months and the pasture progressively displaced the weeds. Lucerne, a moderately salt tolerant crop, was then established and grown for 4 consecutive years (1982-86). Irrigation treatments during this period were saline irrigation (control) and saline irrigation plus gypsum, applied either in irrigation water (4 m.e./L) or on the soil surface (1 0 and 20 /tha). There were no significant differences in dry matter production of lucerne between the control and gypsum treatments during the 3 years after the year of establishment. Mean yields over all treatments were 18 143, 18 375 and 16 700 kg/ha. A decline in yield in 1985-86 was associated with leaf yellowing and brown necrosis and may have been caused by nutrient imbalance. Threshold concentrations of electrolytes were present in the soil whether gypsum was applied or not and, therefore, soil hydraulic conductivity was not affected by saline irrigation. This resulted in no beneficial effect of gypsum applied either in irrigation water or on the soil surface.