section 3: regional examples

Water-harvesting based agroforestry in the arid regions of Israel

H. Lovenstein

Desert Run-off Farms Unit
Jacob Blaustein Institute for Desert Research
Ben Gurion University of the Negev
Sede Bager Campus 84993, Israel

Y. Zohar

Department of Natural Resources (Forestry Section)
Agricultural Research Organization
The Volcani Center
P.O. Box 6, Bet Dagan 50250, Israel

J. Aronson

Boyko Institute for Agriculture and Applied Biology
The Institutes for Applied Research
Ben Gurion University of the Negev
Be'er Sheva 84110, Israel

Abstract

A long-term project was initiated to develop sustainable agroecosystems for the production of food, fodder and firewood under rainfall-harvesting conditions in an arid region. The study is conducted in the Negev desert at the experimental sites of the Desert Run-off Farms Unit in Wadi Mashash and Avdat, where the mean annual rainfall amounts to only 115 and 80 mm, respectively.

Relying entirely on run-off water, research is carried out along the following lines:-

• Plant introduction, with particular emphasis on Prosopis, Eucalyptus, Acacia and Atriplex spp.

• developing appropriate cropping systems based on the agroforestry concept, whereby the following aspects will be monitored in relation to water use efficiency.

• combinations of trees, shrubs and annuals

• plant densities

• optimum coppicing cycles

• fertilization at planting

• animal studies.

Introduction

For nearly thirty years, the Desert Run-off Farms Unit of the Ben Gurion University of the Negev and the Hebrew University of Jerusalem have studied methods to recreate and improve the rainfall harvesting methods developed 2400 to 1500 years ago. These studies have been carried out at experimental sites in Shivta and Avdat (mean annual rainfall 80 mm), located 70 km respectively south-west and south of Be'er Sheva (Evenari et al. 1982).

Based on obtained results a pilot farm was established in the early 1970s at Wadi Mashash (mean annual rainfall 115 mm, located 20 km south of Be'er Sheva, 31° 08'N, 34° 53' E, elevation 400 m asl, 60 km from the Mediterranean. All three locations are characterized by Köppen climate BWhs and BShs (winter rainfall in hot deserts, hot steppes) and by Thornthwaite moisture index, 40 - 60.

Starting with the successful cultivation of a wide variety of orchard and field crops, a major effort is now under way to develop new crops, cropping systems and applications of water-harvesting techniques, with particular emphasis on the needs and problems of people inhabiting the arid and semi-arid regions of the world. With water as key factor a well-defined relationship needs to be established between water supply — the water-harvesting system, and water use — the management of various intensified agrosystems to achieve maximum biomass production per unit of time, area and water.

Water harvesting

Farming based on rain-water harvesting is a system which allows agricultural activity in areas that normally do not receive enough rainfall, by concentrating rainfall-induced runoff from a catchment area into a smaller cultivated area. When rain intensity exceeds the infiltration rate of the soil, water is not absorbed by the soil and hence runs off along the surface to the low-lying parts. A catchment area is therefore characterized by sloping surfaces with low infiltration rates. The cultivated area, however, often comprises a similar soil type and earthen walls need to be erected to retain the accumulated runoff water, allowing for deep infiltration. This requires deep soils with a high water-holding capacity, storing enough water to support plant production during the dry season. Based on this principle, various water-harvesting systems are in use, such as:

• terraced wadis (dry river beds, carrying water during high- intensity rains), sometimes constructed with conduit channels, tapping runoff water efficiently from adjacent hill slopes;

• diversion systems, where erratic flash floods in wadis are partly diverted to adjacent fields using diversion channels;

• macro-catchment basins ('limanim'), where runoff is collected from tributaries and artificially trapped in natural depressions with areas ranging from 0.3 ha to 0.5 ha; and

• micro-catchments, where runoff from a relatively small catchment area is harvested for the support of single trees.

Relying entirely on locally available materials, research is carried out to obtain higher run-off efficiency rates as well as to design water-harvesting schemes with a minimum amount of maintenance and repair.

Plant introduction

Plants, mainly those native to arid lands, are screened for their potential for production of food, fodder and firewood, the three most pressing needs in arid and semi-arid regions of many developing countries. The criteria for selection include: capacity for rapid growth; reliable regrowth after harvesting by coppicing (in the case of fodder trees and shrubs); acceptability as food and/or fodder, especially under current conditions; and finally, ecological adaptability to prolonged droughts, and brief, intermittent periods of flooding in the catchment basins. Most promising species are Prosopis spp. and Acacia salicina for fodder and firewood; Eucalyptus occidentalis and E. camaldulensis for firewood; Leucaena leucocephala for food, fodder, firewood and timber; Atriplex barclayana, A. nummularia and Cassia sturtii for fodder; and Phaseolus acutifolius (-tepary bean) as food crop.

Cropping systems

Once promising plant candidates are identified, more agronomical studies are carried out. Based on the agroforestry concept various combinations of trees, shrubs and annuals are established in various densities to assess overall biomass production in relation to water use. Deep-rooting trees may exploit the deeply infiltrated runoff water, while annuals extract water from the shallow soil layers. As different plant species show different demands of water at different seasons over the year, a temporal and spatial arrangement is thus created in water uptake. Furthermore, trees, because of their solar radiation-intensity-reducing and wind-breaking properties, can create favourable growth conditions for various under crops. For this purpose E. occidentalis and A. salicina are grown separately or mixed with sorghum and chickpea in different densities. Soil moisture depletion from the various soil layers is recorded through a comprehensive network of neutron access tubes, and water use by the different plant species is calculated. These are related to biomass production and plant development stage. Finally a crop simulation model will be assessed.

The above-mentioned trees are also tested for optimum coppicing cycles of 2,3 and 4 years (Zohar 1974) under different plant densities of 600-1200 trees/ha. Depending on the regeneration capacity of the coppice shoots, an optimum harvesting management scheme can thus be determined (Zohar et al. 1986).

Additional experiments involve initial fertilizer application during planting to boost yield and soil tillage.

Animal studies

Animals such as sheep, goats and camels are integrated with these cropping systems. Grazing trials are performed to check fodder quality of different plants, fodder quantity uptake, timing of fodder application, and grazing conditions in relation to food conversion rates.

Conclusion

With a more concentrated water supply, management practices can be more intensified, creating possibilities for the development of agroforestry in arid and semi-arid lands.

Acknowledgements

This project is supported by GIFRID. We gratefully acknowledge the help of staff and volunteers of the Avdat and Mashash farms in the execution of the various projects described herein.

References

Evenari, M., L. Shanan and N. Tadmor. 1982. The Negev, the challenge of a desert. Cambridge, MA: Harvard University Press.

Zohar,Y. 1974. The autoecology of Eucalyptus occidentals Endl. Unpublished Phd. thesis, Tel Aviv University, Ramat Aviv, Israel. (Hebrew, with English summary)

Zohar, Y., J A. Aronson and H. Lovenstein. 1988. Cultivation of multi-purpose trees in rain-water harvesting systems in the arid zone of Israel. Commonw. For. Rev. (submitted)