Growth and ground water uptake responses of lucerne to changes in groundwater levels and salinity: lysimeter, isotope and modelling studies

Shallow saline water tables underline large areas of the Riverine Plains of the Murray Basin of southern Australia. It is believed that deep-rooted perennial plants in these areas are able to reduce recharge and use shallow groundwater, thus controlling groundwater levels. Lysimeters represent the best experimental technique for investigating capillary upflow from shallow water tables and the associated processes of salt accumulation, plant water use, and growth response. Techniques involving stable isotopes of water help determine the components of upflow due to vegetation. When combined with models that stimulate salt and water movement in the soil zone and the plant water use and growth, we can thoroughly test our understanding of salinity processes and the ability of plants to control water tables. Results from WAVES simulations of plant growth, evapotranspiration, groundwater uptake, salt accumulation, and the impacts on lucerne growth are compared against measurements made in lysimeters at Griffith, NSW, Australia. With minimal calibration, WAVES was able to reproduce both the daily and seasonal variation in evapotranspiration, upward flux from the groundwater table, plant growth in terms of leaf area development, soil water profiles, soil water salinity, and root water extraction patterns. There was a decline of 36% in transpiration, 42% in leaf area growth, and 67% in upward flux after the salinity of the water table increased from 0.1 to 16 dS m(-1). Although the upward flux of water was large, lucerne used little of it (< 20%), preferring 'fresher' rainfall and irrigation water near the surface. Given the tests presented in this work, we think WAVES is applicable to irrigated agricultural systems. (C) 1999 Elsevier Science B.V. All rights reserved.