Plant uptake of water from a water table

ACCORDING TO ONE ESTIMATE 36 PERCENT OF THE AREA CONSIDERED ARABLE IS UNDERLAIN WITH SALINE WATER NOT SUITABLE FOR IRRIGATION. HOWEVER, THERE IS A THIN FRESH WATER AQUIFER OVERLYING THIS SALINE WATER ZONE. DEEP PUMPING IS NOT POSSIBLE IN THIS AREA. A SUGGESTION HAS BEEN MADE THAT FRESH WATER BE COVERED BY INSTALLATION OF LOW CAPACITY SKIMMING TUBEWELLS. ANOTHER SUGGESTION IS THE DIRECT UTILIZATION OF GROUNDWATER BY PLANTS BY INSTALLING OPEN OR CLOSED SUBSURFACE DRAINAGE SYSTEM AND STABILIZING THE WATER TABLE AT A SPECIFIC DEPTH. UNDER THE LATTER SITUATION THE PLANTS WOULD MEET A SMALL PART OF THEIR REQUIREMENTS FROM SURFACE IRRIGATION, BUT A MAJOR PART FROM THE GROUNDWATER RESERVOIR. WITH THIS BACKGROUND A REVIEW OF STUDIES WAS MADE TO GAIN KNOWLEDGE CONCERNING THE ZONE OF WATER UPTAKE SO AS TO ESTIMATE THE CONTRIBUTION OF GROUNDWATER AVAILABLE TO PLANTS. THIS KNOWLEDGE WAS ALSO SOUGHT TO PROVIDE AN INDICATION OF THE ZONE OF SALT CONTRIBUTION AND OF NUTRIENT UPTAKE. RESEARCH CARRIED OUT REVEALED THAT UNDER A CONSTANT BOUNDARY CONDITION IN WHICH THE WATER TABLE IS MAINTAINED AT A FIXED SHALLOW DEPTH, IT WAS POSSIBLE TO PREDICT THE ZONE OF WATER UPTAKE. EXPERIMENTAL DATA AGREED WITH PREDICTED PLANES OF WATER UPTAKE. SOIL WATER EVAPORATION DATA INDICATED CA. 90% EVAPORATION TOOK PLACE WITHIN THE UPPER 150CM. THIS LOSS COULD BE AVOIDED BY GROWING SUITABLE CROPS AND KEEPING THE WATER TABLE AT A CONSTANT SHALLOW DEPTH. AT SHALLOW WATER TABLE, DATA SHOWED THAT IRRIGATIONS WERE REDUCED AND THAT SUCH AREAS COULD POSSIBLY HAVE AN ALTERED WATER ALLOWANCE.