Soil-Based Vegetation Technique to Quantify Effects of Rhizospheric Soil Osmotic and Matric Water Potentials on Crop Salt Tolerance

In saline soils, plant water supply is the most critical growth factor. To better understand water supply and growth of soil-grown crops, research should focus on root water uptake in saline soils. Plant water supply and growth is complex. One has to consider, simultaneously, soil and plant parameters: (i) the soil physical parameters texture; pF curve; osmotic, matric and total water potential; salinity at the soil/root interface; and bulk soil salinity; and (ii) the plant parameters root mass and rooting density; root morphology; transpiration; and shoot growth. Technical devices for direct and simultaneous measurement of all parameters are not yet available. This study presents a vegetation technique (VeTe) that permits to determinate required data from continuous measurement of pot water losses and by indirect calculation. The VeTe was tested using young rape (Brassica napus, cv. Lingot) as the model plant, growing in a silty soil. Rape was selected for its efficient root system to explore soil determined growth factors. Basically, the VeTe requires two vegetation phases: a pre-cultivation phase, and an experimental phase. The objective of the first phase is to grow young plants that are homogenous in their shoot and root development through well-controlled water management. Varying rooting densities of soils are performed when plants are pre-cultivated in different soil volumes. The experimental phase starts when plants are irrigated with water of different salt concentrations up to soil water contents of 30 vol.%. During the experiment, plants were grown under well-controlled, climatic conditions, and pot water losses were measured bi-hourly. Measurement of continuous water losses serves to calculate soil moisture contents, derive osmotic and matric heads and their impact on plant transpiration. The proposed technique provides a means for quantitatively studying the combined impacts of soil osmotic and matric stresses on water uptake by crops differing in their root morphologic traits at different rooting densities.