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Central Arava R&D

Blending of desalinated and saline water for efficient agriculture (a 2-yr project)

Background

In the Arava region, desalination is an increasingly feasible solution for generation of water for irrigation. A number of small to medium size reverse osmosis desalination plants already exist in the south of Israel and more, larger facilities are currently planned. Irrigation with desalinated water is beneficial as it allows for increased yields and decreased environmental degradation from leaching of salts. In spite of this, desalinated water lacks a number of minerals which are necessary for plant growth and which must be provided in intensively irrigated agriculture. The minerals calcium, magnesium and sulfur are removed during the reverse osmosis desalination process. Since they are present in all of Israel ’s other water sources they are not commonly added as fertilizers. The missing nutrients can be re-supplied either as fertilizer supplements to the water or soil or, alternatively through blending of the desalinated water with saline water. Blending, is less costly than fertilization and increases the volume of irrigation water but, due to the higher salinity of the blended water, increased leaching rates lead to higher overall water consumption and to elevated pollution of soils and groundwater with salts and other contaminants. Our hypothesis is that plant water and nutrient uptake are acutely reduced as a function of increased salinity in the low salinity range as opposed to current theories that predict only a slight reduction or even a threshold. Proper understanding of plant transpiration and nutrient uptake as a function of salinity can prevent unforeseen yield reduction and excessive application of irrigation water and fertilizer.

 

Methods

Experiments will be conducted in free-standing weighable lysimeters located in a sunken trench receiving irrigation with 3 different salinities (desalinated, blended and saline) and 4 irrigation levels that can accommodate different leaching fractions. The treatments will be replicated to enable translation of the results to grower's practices. Daily results of evapotranspiration will be published on the internet and will also be available to farmers as well as to extension service advisors. Growth, yield, fruit quality, and plant nutrient composition will be recorded for each treatment. Such knowledge will increase productivity and raise water use efficiency together with soil and ground water sustainability.

Objectives

To understand the effect of salinity on plant water and nutrient uptake and to model water flow and nutrient uptake and transport throughout the root zone as a function of salinity. The objectives will be accomplished by laboratory and field experiments on bell peppers and via the use of a numerical model (HYDRUS) to enable prediction of plant growth, water consumption, yield and environmental contamination as a function of management variables.

The research will progress on three scales: 1) highly controlled experiments at the Zohar experimental station; 2) model calibration, development and application at Ben-Gurion University and; 3) semi-commercial greenhouse trials conducted at the Zohar experimental station.

Contact:
Dr. Uri Yirmiyahu

08-9928644