Prospects of agroforestry for the marginal environments: Evidences from the United Arab Emirates

Abstract

Dryland salinity and occurrence of highly saline groundwater are recognized as the major bottlenecks for the agricultural development in the marginal desert environment. In the United Arab Emirates (UAE), about 34% area is affected by salinity. The coastal sabkha areas are highly salinized (28.8 dSm-1), whereas in the coastal region of the Abu Dhabi Emirate, salinity is more than 200 dS m-1. The major causes of land degradation include use of brackish groundwater for irrigation, insufficient leaching of salts and upward movement of saline groundwater in the very hot environments. Rising sea levels along with the over-exploitation of fresh water resources also causes seawater intrusion in coastal zones. In the hyperarid environment of UAE, integrating trees and shrubs with other farm enterprises could be a useful strategy to increase system's productivity. Field studies conducted on UAE soils have shown that Acacia ampliceps can fix nitrogen under different salinity levels ranging from 10 dS m-1 to 30 dS m-1, thus supporting the nutrient requirements for the two grasses, i.e. Sporobolus arabicus and Paspalum vaginatum. The average yield of these grasses varied from 22 to 28 Mg dry matter ha-1 year-1. In addition, the foliage from the trees harvested at 2 m from the ground surface additionally provided ~10 Mg dry matter ha-1 year-1. The A. ampliceps trees showed nodulation even at 30 dS m-1 with the bacteria showing the characteristic feature of gram-negative Rhizobium. The fixation of nitrogen by the Acacia trees helps in increasing the soil nitrogen through the root system and supporting the forages. In the (sabkha) coastal areas, establishment of halophytic plants such as Atriplex species can be advantageous due to low annual maintenance costs and their ability to survive high salt contents in the soil. As conditions become less severe, it will be possible to plant non-halophytic trees, shrubs and grasses. For UAE, a total of 76 halophyte species have been identified. Among these, 14 are seawater-tolerant halophytes, 29 as halophytes, 31 as semi-halophytes, and 2 are parasitic plants thriving on the roots of members of Chenopodiaceae and Zygophyllaceae family. The evaluation, domestication and large-scale utilization of native and introduced halophytes and salt-tolerant plant resources in sole or mixed farming system would have a significant impact on salinity control and remediation as well as on the economic development of salt-affected dry regions.