Response of Medjool dates to Boron under conditions of salinity

Introduction

Boron is an important element in association with plant development and agricultural production. Boron in some soils and irrigation waters reaches concentrations that are found to be toxic to plants. Commonly, boron toxicity occurs in arid regions where irrigation water contains high boron. These regions are often also associated with high water demands for plants and with high salinity in soils and irrigation water. In the Southern Arava Valley, date plantations are traditionally irrigated with saline water. Today, many orchards have switched to effluent water. Effluent from municipal sources in arid regions is commonly both saline and high in boron content. Municipal effluent from the city of Eilat is particularly high in boron. This is due to much of the city's water supply originating as sea water and that the current method for desalination used leaves high levels of boron.

Date palms are regarded as tolerant to salinity (Fur and Armstrong 1962, Maas 1984) Maas reports threshold value of 4dS·m-1 for onset of yield decrease. Later works (Aljaburi 1997, Hassan 1990,1993) show that date palms are salinity tolerant due to osmotic compensation brought about by concentration of sodium and calcium in the leaves. Meiri (1997, 1993) found that increase in irrigation water salinity resulted in decreased vegetative growth rate. Several of the researchers document an increase in fruit quality with increased irrigation water salinity. In general, there is very little literature regarding boron in date production. The USDA salinity laboratory in Riverside California has classified date palms as very tolerant. This classification is based on observations and not on controlled experimental work. There is no documentation of response to high salinity and high boron together and therefore it is not known whether cumulated or additive effects are expected under such conditions or if one of the stress causing factors will be dominant.

Field experiments attempting to address questions of irrigation quantity and quality in date production are complicated and expensive for several reasons. First, the root system of the date is large and extensive; diameter of the area containing roots can reach 10-15 meters per tree. Therefore, separation of treatments demands extremely large areas and plots. Second, the date has a “long memory”. Yield response and other physiological responses occur up to a year after stress is experienced. Third, the investment in establishing a new orchard is high and therefore it is not practical or possible to apply treatments which will cause real damage to commercial orchards. Without such treatments, it is impossible to truly learn plant response to salt and boron caused stress.

In order to overcome the stated problems, this project considers the issues from two approaches:

  1. Lysimeter study of combined boron – salinity response.
  2. Statistical analysis of data collected from commercial date orchards in the Arava Valley irrigated with a variety of water sources.

Lysimeter Study

At the Arava Research Station at Yotvata, Israel, 20 Medjool variety date palm trees from tissue culture were planted in large (1 m3) lysimeters in local topsoil (Arava sandy loam) in the fall of 2000. A year after planting, after the trees had developed sufficient root and canopy systems, experimental treatments began. The lysimeters are irrigated with water containing combinations of 4 salinity levels and 5 boron concentrations. Salinity levels are0.5, 4, 8 and 12 dS·m-1 and boron concentrations are 0.3, 2, 5, 20, and 40 mg·l-1 B. The lysimeters are each irrigated with 120% of their actual evapotranspiration measured daily.

Throughout the experiment the relationships between boron and salt and the consequences of both of them, individually and together on date growth and production are monitored.  Among the measurements made are:

  1. Visual signs of stress
  2. Boron, Cl and Na concentrations in leaf and root plant material, in soil and in leachate.
  3. Total water use (actual evapotranspiration).
  4. Evapotranspiration rates over the course of a day and over the course of the season.
  5. Growth rates and yields.

Results from the experiment are used to determine crop response functions to salinity and to boron. Results will be compared to those from running the models which predict water use and growth based on climate and crop data.

In the winter of 2002-2003, dates were transferred to 2.5 cubic meter lysimeters each of which sits on a scale providing ongoing monitoring of weight of system. Fruit harvest is expected from 2004. Results from the experiment so far can be found in the “reports” section.

Funding

We are appreciative of funding for the project provided by:

  • The Jewish National Fund
  • JCA Charitable Foundation
  • Israeli Fruit Growers Association – Date Board.
  • Chief Scientist Israeli Ministry of Agriculture

References

  • Aljuburi, H.J. 1996. Effect of salinity and Gibberllic acid on mineral concentration of Date Palm seedling. Fruits. Elsevier. Paris. 51, 429-435.
  • Furr, J. R., Armtrong, W. W. 1961. A test of salt tolerance of mature Halawy and Medjool Date Palms. Date Growers’ Institute. Rep 39, 11-13.
  • Hassan, M .M., Abu-El-Azayen, A. L. 1990. Differences in salt tolerance of some fruit species. Eghpt J. Hort. 17,1-8.
  • Hassan, M .M., El-Samnoudi, I.M. 1993. Salt tolerance of Date Palm trees. The Third Symposium on on Date Palm, King Faisal University, Date Palm Research Center. Saudi Arabia. 17-20.
  • Maas, E. V. 1984. Salt tolerance of plants. In: Handbook of plant science in Agriculture, B.R. Christie, ed. CRC Press, Inc., Cleveland, Ohio.
  • Meiri, Rueveni, Lerner, Sharbani, Zaidel, Solomon 1993. Irrigation water response on growth and yield of date palms report from 1991-1993. Annual Report, Agricultural R&D, Jordan Valley, Israel. In Hebrew.
  • Meiri, Rueveni, Lerner, Solomon, Yishchar, Rozner 1997. Vegatative growth, yield, and fruit quality of dates in response to salt and water stress. Annual Report, Agricultural R&D, Jordan Valley, Israel. In Hebrew.