Incidence de la salinité sur les cultures irriguées

Abstract

The effects of irrigation water quality on plant growth is predictable. The haricot bean was considered in this study, because of its high sensitivity to NaCl, which was found to have the same effect on crop output in bath sail and nutrient solutions. The study was limited to consideration of a nutrient solution, which is easier to handle, gives accurate results and is representative of local soil conditions. Separate investigation of factors governing the effect of salinity on the haricot bean showed that : 1. Leaves are more sensitive to NaCl than pods and stalks. 2. Plant sensitivity increases under bright illumination. 3. The stage of growth at which the plant reacts most strongly to salt is between the first seedless leaf and flowering. Afterwards, salt-sensitivity can no longer be determined. This will no doubt be of interest to farmers planning irrigation. 4. At osmotic pressures in excess of 2 atmospheres, plant yield is totally unaffected by the salt causing the osmotic pressure rise. Below 2 atmospheres, yield increases with osmotic pressure if the pressure rise is caused by nutrient salt concentration, but decreases if salts are responsible (especially NaCl, and to a lesser degree Na2SO4). Owing to the decisive effects of environmental and equilibrium factors, considerable caution is advisable when evaluating loss of yield due to salinity. These factors must be known for all practical evaluation purposes. An overall evaluation of loss of yield due to salt can be simulated by a linear model, except at low concentrations, for which this type of model is probably no longer representative. The effect of salinity in the considered zones was studied by two experimental methods in which observation of the effects of NaCl was based on water absorption and photosynthesis. Attempts to determine a critical salinity value were unsuccessful. High Cl concentrations (0.75-2 g/l) apparently produced less depressive effects. Irrigation and soil water salinities were also related by a linear model. Hence, there is a linear relationship between haricot bean pod output and irrigation water Cl concentration, from which the effect of salt pollution on plant yield can be predicted.