Soil and groundwater salinity has emerged as the most significant agricultural problem facing the Sultanate of Oman. Scant rainfall, coupled with high temperature, is always conducive to the accumulation of salts in soils. These conditions are predominant in Oman. Secondary soil salinity has increased at a very rapid rate due to the persistent use of saline groundwater, which, over time, has become more concentrated due to increased pumping by farmers in the Batinah region - the country’s most important agricultural area.
The balance between total pumping and annual recharge that had existed prior to the 1990s has been greatly disturbed, resulting initially in reduction of crop yields and gradually in the abandonment of lands. Saline seawater intrusions are also present in some areas of the region that are nearer to the sea as the result of over-pumping. Salt-affected lands constitute about 44% of Oman’s total geographical area and 70% of the agriculturally suitable area of the country. The annual losses due to salinity have been reported as 7.31 to 13.97 million Omani Rials (2005 data, 1 Omani Rial = 2.58 USD). When salt-affected lands go out of cultivation, their owners become unemployed - engendering a host of socioeconomic problems. Clearly, therefore, soil salinity poses a huge threat to the sustainability of agriculture in Oman, especially in Batinah.
The research project “Management of Salt Affected Soils and Water for Sustainable Agriculture,” prepared and approved by Sultan Qaboos University, was undertaken to explore ways to mitigate soil and water salinity. The project focused on four approaches: soil rehabilitation, bio-saline agriculture, fodder production, and the integration of the fish culture into crop production that could have compensatory economic returns to farmers. The project aimed at developing management guidelines which are scientifically sound for farmers a) to sustain economically viable agricultural production in salt-affected areas with saline groundwater, b) improve food security of Oman, and c) combat desertification. The idea was not to try to remove all salts from soil and groundwater but to learn to live with the prevailing conditions by providing sufficient income to the farmers in the affected areas through various means. The project was conducted with the active participation of Omani government scientists, farmers, and international experts. The tasks accomplished during the project include:
Assessing the intensity and extent of salinity in the Batinah region using remotely sensed satellite images, ground-truthing, and preparation of temporal and spatial variation maps of salinity of soil and water from GIS.
Determining agronomic solutions (mulching, tillage, sowing methods, etc.) and nutritional aspects including microbial nitrogen mineralization in saline conditions.
Determining engineering and water management solutions (irrigation, sub-irrigation, leaching, leveling, etc.) to reduce water loss and salinization.
Determining biological solutions by identifying salt-tolerant crops and fruit trees for various salt-affected regions of Oman. This includes introduction of halophytes.
Assessing the effects of feeding salt-tolerant forage crops to Omani sheep.
Integrating fish culture in marginal lands.
Determining socio-economic costs and benefits of salinity management practices in the Batinah region.
Findings from the project confirmed that:
Salt-tolerant varieties of tomatoes, barley, sorghum, and pearl millet can be grown successfully in saline soils of the Batinah coast. It was possible to grow such crops with saline irrigation of 6-9 dS/m water (1 dS/m water is equivalent to 640 ppm of salts). Tomato (Ginan variety) was best grown with irrigation water of 6 dS/m and by adding mixed fertilizer (organic and mineral in 1:1 combination).
Mulching surface soil with a thin layer of shredded date palm residues resulted in lesser salt accumulation in the soil resulting in more crop yield than other methods.
Fodder (sorghum) grown in saline soils with saline water has no negative effects on growth or meat quality of goats.
Incorporation of aquaculture (using red hybrid tilapia Oreochromis sp.) in saline areas was proven feasible and could partially compensate for salinity induced crop losses. Nutrients in water that come out of fish ponds enhanced crop growth.
The project has shown that under careful management, it is possible for farmers to make a living from salt-affected lands by adopting various techniques such as appropriate use of salt-tolerant crops, fertilizers, and mulches; and by diversifying into non-traditional areas of income generation such as aquaculture. This low-cost system for treatment of greywater and low quality surface water, if adopted on a large scale, will contribute to the overall environmental sustainability by lessening demands on freshwater resources in many countries of the world.