IRRIGATION WITH BRACKISH WATER IN SOILLESS CULTURE
Higher nitrate and potassium levels are recommended, phosphorus and iron levels should be lowered and added more frequently in order to reduce precipitation of ions.
More frequent irrigation is required to avoid the raising of the osmotic pressure of the nutrient solution remaining between gravel or coarse sand as growth media and a good drainage system. A more frequent replacement of the nutrient solution is recommended.
The use of brackish water in hydroponic systems for commercial crops has been practiced in Israel, Canary Islands, Sicily and North African countries for several years, and this paper summarizes shortly the observed results concerning nutrition conditions.
Brackish or saline water, we define as water from sources that have a total salinity of 2 500 – 3 500 ppm, and contain mainly clorides and sulfates of 700 – 1 000 ppm, sodium and calcium of 300 – 500 ppm, and 120 – 200 ppm magnesium. These concentrations are typical in brackish water springs in the southern part of Israel, the Arava, or near the Dead Sea.
By a commercial hudroponic system we mean primarily, the gravel culture system, but also sand-culture (coarse sand of 1 mm grains) methods.
We assume that under saline stress conditions, disturbances in plant development result originally from nutritional disorders and hampered environmental conditions, especially root aeration.
What is called "an optimal nutrient solution" like a Hoagland solution, and its nutrient ion concentration, is not the same under saline conditions. The interactions of the various nutrients in the saline environment, their absorption and incorporation in the plant, and their effect on yield was only partly investigated, and depends on the crops and on plant growth stage.
The general statements presented in this paper, are to some extent a result of the mentioned researches, but are mainly a result of field experience. These observations are restricted generally, to tomatoes, cucumbers, squash and carnation.
Under saline conditions:
nitrates - should be raised from 5 to 7 or 8 mM,
potassium - no change is recommended (6 mM),
phosphorus - should be reduced to 1 mM from 3 mM, because a relatively high phosphorus level causes precipitation of iron and