Management of desalinated water for irrigation of peppers

1. Management of desalinated waterfor irrigation of peppers Alon Ben-Gal Agricultural Research Organization Gilat Research Center Plant response to salinity and implications regarding blending strategies מים מותפלים לחקלאות בערבה – היבטים אגרונומיים ויישומיים 07/10/2008

2. Why use desalinated water for irrigation? • Better plant growth • Reduce leaching requirements • Higher yields with less water • Less negative environmental impact (sustainability)

3. Lysimeters Yotvata 2 seasons 9 salinity levels 3 water (leaching fraction) levels Determination of Eta, drainage water quantity and salinity, biomass production and yields Ben-Gal A., Ityel E., Dudley L., Cohen S, Yermiyahu U, Presnov E, Zigmond L, Shani U. (2008) Effect of irrigation water salinity on transpiration and on leaching requirements: A case study for bell peppers. Agric. Water Manag. 95, 587-597.

4. Greenhouse experiments Zohar and Yair stations Desalinated water (EC = 0.4-0.5 dS/m) Saline water (EC=2.5-3.2 dS/m) Blended water (30% saline; EC=1.35 dS/m)

5. Under experimental conditions: sandy loam soil and high evaporation demand – irrigation water salinity causes reductions in transpiration and subsequent reductions in vegetative growth starting within 1 month of planting Ben-Gal et al., 2008. Agric. Water Manag.

6. Relative water application (leaching fraction) influences response – increased leaching maintains lower soil solution salinity) Ben-Gal et al., 2008. Agric. Water Manag.

7. Shani, U., Ben-Gal, A. Tripler E. and Dudley, L.M. (2007) Plant Response to the Soil Environment: An Analytical Model Integrating Yield, Water, Soil Type and Salinity. Water Resources Res. Vol. 43, No. 8, W08418 10.1029/2006WR005313. I/ETp

8. Ben-Gal et al., 2008. Agric. Water Manag.

9. Blending as a strategy to save water and nutrients? 3 years of data from experiments in Zohar station Ben-Gal A Yermiyahu U and Cohen S. (2008) Fertilization and blending alternatives for irrigation with desalinated water. J Environ. Quality. In press.

10. Ben-Gal et al. (2008) J Environ. Quality. In press.

12. Ben-Gal et al. (2008) J Environ. Quality. In press.

13. Ben-Gal et al. (2008) J Environ. Quality. In press.

14. Conclusions (I) • Irrigation water salinity needs to be evaluated in terms of: • reduced crop yields • direct cost of additional water needed to leach salts • indirect environmental costs of leaching

15. Conclusions (II) • For the relatively salt-sensitive pepper crop grown in an arid region, reducing salinity from EC 3.20 dS m-1 to EC 0.40 dS m-1 by reverse-osmosis desalination was found to increase maximum yields by almost 50% while allowing a reduction of the applied irrigation water to half of that with the saline water. • However, the cost of fertilizing in order to re-supply Ca, Mg, and S minerals removed during the desalination process (in our case some $3,500 ha-1) must also be considered. • Pepper yields from irrigation with blended water containing 70% desalinated and 30% saline water could be maintained at greater than 90% of those with fully desalinated water, but only if irrigation rates were increased by at least 50%. • The blending strategy for providing mineral nutrients can therefore consume up to 40% more desalinated water than the fertilization strategy. • The environmental cost of the increase in irrigation-water salinity from an EC of 0.40 dS m-1 (desalinated water) to an EC of 1.35 dS m-1 (blended water) is substantial, as it involves the loading (into the soil) and leaching (beyond the root zone) of five times more salt, and potentially escalates the transport of other contaminants out of the root zone as well