Israeli researchers are calling for a reassessment of the use of desalinated water for irrigation, warning in an article published in today's issue of Science Magazine that desalinated water adversely affects some crops, such as tomatoes, basil and certain varieties of flowers.
Israel's use of desalinated water for agriculture is the highest in the world, so the new research is arousing considerable interest among scientists.
Much of the water produced in Ashkelon's desalination plant is used for irrigation. This is the world's largest seawater reverse osmosis (SWRO) plant, producing some 100 million cubic meters of desalinated water a year. Dr. Jorge Tarchitzky, head of the Agriculture Ministry's department of soil and fertilizer usage and one of the article's authors, says the plant produces more water than required for urban use, and half of it is funneled to agriculture.
The article says that the water's the low mineral content, once believed to be an advantage, is bad for the crops. Calcium shortage, for example, causes physiological defects, while magnesium shortage damages the plant's development.
If the crops are grown in sand or off the ground, the damage is even worse, because the soil cannot provide the missing elements. Frequent changes in the water's composition hurt the crops still further.
"One morning we woke up and found that only desalinated water was flowing through the pipes," said another co-author, Dr. Uri Yirmiyahu of the Gilat Research Center. "We gradually began to see the problems. For example, a shortage of magnesium damaged the development of tomatoes and caused defects in basil."
Added co-author Dr. Asher Bar-Tal of the Agricultural Research Organization - Volcani Center: "The problem is the irregular water composition. Sometimes the desalinated water is adulterated and sometimes it isn't. The damage is reflected in the crops' quality."
"The Agriculture Ministry gave farmers a solution - a system that reports changes in the water's composition," Yirmiyahu said. "But the farmer must be prepared for such changes at any given moment. The changes used to be seasonal, which they could handle. Now, the change could take place within a few hours and the water's quality must be checked all the time."
The tender for the desalination plant set criteria only for the quality of drinking water. The researchers are calling for new standards that would also require the desalinated water to be suitable for farming, by requiring it to contain some of the nutritional elements vital to crops.
"Israel is first in the world in setting criteria for desalinated water and has managed to raise this water's quality. Now the water quality must be improved for both farmers and urban consumption," said a fourth co-author, Dr. Ori Lahav of the Technion.
Dr. Alon Tal of Ben-Gurion University and Dr. Alon Ben-Gal of Gilat also took part in the study.
The financial cost of improving the water may determine whether and how any changes are made.
"Our proposal is a compromise," Yirmiyahu said. "The water would still not be perfect for agriculture, but it would be less harmful. We got together with several researchers from various disciplines to compose an article calling attention to a world problem. Water shortages are becoming more common - in Australia, California, China, Spain and, as ever, the Middle East. Given this looming crisis, it is obvious that desalination is the front-line defense, and so all the implications of its use must be considered."
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