Exploring sea water chemistry for farming
The surface water is becoming scarce with the ever-increasing cropping intensity. There are not enough water reservoirs and the rains have gone scanty. Not long go the water crisis had claimed many human lives in Cholistan and Balochistan.
In this scenario of water crisis, sea water is the only hope. Time has come to imagine about economical use of sea water. If we discover the use of sea water for crop production, there will be no desert, no barren land - but all green. It is high time to think of seawater farming and sand dunes.
A team of scientists with experience in genetic engineering, soil and water must come forward with an idea of a blue revolution after the green one. Before strategising the options for judicious harvesting of sea water, there is a need to explore sea water chemistry in the light of present knowledge base.
Sea water chemistry: The liquid structure of hydrogen and oxygen gases being a universal solvent gets a number of anions, cations or radicals dissolved to it. The sodium, magnesium, calcium and potassium are the influential cations, while the chloride, sulphate and bicarbonate make the major anions.
Analysis of water of the Arabian Sea at Karachi reveals a sodium concentration up to 491 milli equivalents per litre. Next to sodium, magnesium amounts to 122 milli equivalents per litre.
Calcium, by and large, does not go beyond 20 milli equivalents per litre. Regarding anionic fraction of the dissolved substance, the concentration of about 580, 60 and 3.0 milli equivalents per litre is estimated for chloride, sulphate and bi-carbonate ions, respectively.
According to geochemical system of classification, sodium chloride, and magnesium chloride are the foremost salts, while the calcium chloride and calcium sulphate may be present in lesser quantity. Bicarbonate salts of calcium and magnesium may have still very low concentration.
Let us analyse the sea water problem in its true perspective. The sodium adsorption ratio, residual sodium carbonate and electrical conductivity are often used as conventional water quality indicators, each having a corresponding tolerable limit of less than 10, 2.5 milli equivalents per litre and 1.5 deci Siemens per metre.
Seawater has an electrical conductivity range of 35 to 45 deci Siemens per metre and a sodium adsorption ratio of about 60. The residual sodium carbonate of sea water is not a predicament. The residual sodium carbonate of water has a negative value of about 139 milli equivalents per litre. The high sodium adsorption ratio and electrical conductivity of sea water are the most important constraints that limit its use in agriculture.
The use of water with high electrical conductivity and sodium adsorption ratio on normal soils in the absence of any scientific intervention will tempt both salinity and sodicity problem in soils.
Another chemical characteristic of seawater reveals a mono-valent to divalent ratio of about three to one. The sodium to calcium ratios of 26 to one and calcium to magnesium ratio of one to six have been worked out from sea water chemistry.
The experts elucidate that for initial use of highly sodic soils (with low permeability) a mono-valent to divalent ion ratio should be more than three.
Conversely, the magnesium contributing to this ratio has sufficient size. Magnesium when in excess behaves like sodium which reduces the hydraulic conductivity of soil.
Sea water use strategies: In view of ever intensifying demand of water in agriculture sector the research endeavours must be strategised for seawater use.
At present, reverse osmosis like technologies may help desalinise sea water, but these are not cost-effective at the time. Similarly, filtration techniques can’t confront heavy salt flux of sea water to maintain their integrity.
Use of selective resins and sand pipes may be a road to seawater harvesting. We may benefit from the past experience in this regard.
Few years back the water project of Bahria for making sea water fit had started during the regime of Gen Zia-ul-Haq which had yielded very encouraging results.
The project akin to this taken up by the PCSIR laboratories, Quetta, for sweetening sea water was also reported for its good out put.
To trim down salinity and sodicity effects of sea water on soil and crops, a number of aspects have to be researched out. The sea water may be enriched with gypsum to deliver sufficient calcium, a panacea to dense sodic soils.
Thus adequate calcium enriched sea water can help in initial reclamation of the sodic soils. However, researchers have indicated that the brackish water having calcium to magnesium ratio up to 1:6 is safe to grow rice and wheat during the reclamation of saline-sodic soils with chemical or organic soil ameliorants.
The use of sea water when blended with canal water can be planned effectively for deserts. We should have a go to pilot projects in such practicable areas.
The desert soils having sandy texture cannot hold sodium as much as clayey soils can. Such soils if properly applied with plant nutrients can be used to raise crops tolerant to sea water salinity and sodicity.
It has been observed that none of the top edible crops - wheat, rice, corn, potatoe and soybean - can tolerate sea water salinity and sodicity.
All these plants droop, shrivel and die within days when their root system is exposed to sea water. Only salty crops can tolerate to different degrees.
The salty crops or halophytes have salt tolerance mechanisms of their own. They accumulate the salts in a particular body section with specialised anatomical features such as salt glands.
Dilution of sea water may be another opportunity. While analysing the conventional water quality indicators we recognise that high electrical conductivity water requires dilution with good quality water to prop up its use for irrigation.
Based on conservative calculations, the sea water with an electrical conductivity of about 35 deci Siemens per meter needs 99 times dilution to bring it to permissible limit of say one.
Similarly a dilution factor of 100 times is computed to trim down the sodium adsorption ratio of sea water to the permissible limit of six.
In broader sense, almost from electrical conductivity or sodium adsorption ratio point of view, the 100-time dilution of sea water with canal water will make the sea water fit for irrigation.
If 100 MAF water is taken as average water running through the Indus River System (IRS) then at the country-level about one million acre foot sea water can be used for raising about one million acres of wheat crop assuming that one acre foot water shall be sufficient to mature a wheat crop.
This may generate an income worth Rs16, 600 millions at the rate of Rs415 /mound if every well managed acre produces an average yield of 40 mounds.
The benefit from rice crop which is transplanted as a kharif crop with the same quantity of water about 1.5 lakh acres of rice crop can be grown.
This would be an added plus income. This highlights the need to imagine the dilution factor at country-level through specially designed dilution regulatory headworks at suitable sites in the provinces.
Through efficient drainage system, soil selection and bio-saline technology, the diluted sea water can be put to use in certain areas. However, experts report that sea water agriculture must fulfill two requirements to be cost effective.
First, it must produce valuable crops at yields high enough to rationalise the expense of pumping irrigation water from the sea.
Second, researchers must develop agronomic techniques for growing sea water-irrigated crops, shrubs and trees in a sustainable manner - one that does not harm the environment.
The dilution regulatory head works in different regions should operate on the basis of switch-over mode of irrigation i.e. one part of the feasible region should receive canal water without mixing with the sea water, while the other one must have canal water blended with the sea water.
The dilution of sea water with available canal supplies in conformity with salt tolerance limits of crops may also increase the water allowance to the fields.
The cropping patterns need to be revised in context of water inadequacy in the country. The area under conventional fodder crops for example, needs to be condensed in certain parts of the country.
Such regulatory head works may be operated during emergency period or whenever augmentation of canal water supplies is mandatory. Policy makers are suggested to try this project exercise at suitable sites so as to learn from its success or failure.
Halophytic plants: Halophytic plants highly tolerant to salinity and sodicity may be cultivated in a proportion to the conventional fodders. The atriplex species such as atriplex amnicola and atriplex undulata can hold up salinity up to 33 and 23 deci Siemens per meter with 50 per cent reduction in yield.
Similarly, Leptochlova fusca locally known as Kallar grass can produce a satisfactory yield with a water having high salinity or sodicity.
It can tolerate salinity up to 22 deci Siemens per metre with only 50 per cent reduction in yield.
The Kallar grass can grow in saline-sodic soils even when irrigated with brackish water. High salt tolerance, capability to grow with saline irrigation water, better utilisation of solar energy, biological nitrogen fixation and its ameliorative effects on salt-affected soils makes the Kallar grass an ideal plant for salt-affected soils.
Green matter production to the extent of 40 tons per hectare is well documented from its cultivation. So dilution of sea water may help increase an area under the Kallar grass.
Researches also reveal that their mixing with conventional fodder crops increases milk production and help them gain weight for meat production.
Thus the Kallar grass or atriplex species can be mixed with fodder crops and dried up as food for livestock. Such dried and stored food can help save livestock in a drought-hit region of Cholistan.
Gene bank: Research on gene bank is also an emerging subject in the future. The genetic engineers must come forward with salt-tolerant gene bank and induce salt tolerance to agricultural crops.
Such institutions must be given target in this context. For salt tolerance the genes need to be translocated and transplanted in different plant species. Limiting to simple salt screening mechanisms will not serve the intention.
The Kallar grass in sea water agriculture can be used effectively to extract ethanol, prepare paper and grow mushrooms on its biomass.
Besides selective breeding and genetic engineering strategies our approach should target the domestication of wild salt-tolerant plants for use as forage, food and oilseed crops.
Some of most productive and salt-tolerant halophytes are shrubby species of salicornia, suaeda (sea blite) which contain about 15 to 20 per cent of all halophyte species. Among the salt-tolerant plant salicornia bigelovii is a promising halophyte.
It is a leafless, succulent, annual salt – marsh plant that colonises new areas of mud flat through prolific seed production.
The seeds contain high levels of oil (30 per cent) and protein (35 per cent), much like soybeans and other oilseed crops the salt content is less than three per cent.
The oil is reported highly poly-unsaturated and similar to safflower oil in fatty acid composition. It is extractable from the seed and can be refined with conventional oil seed equipment.
It is also edible with a nutlike taste and a texture similar to olive oil. However, a small draw back is that the seed contains bitter compounds e.g. sap nine that make the raw seed inedible. These do not contaminate the oil, but remain in meal after oil extraction.
Many prototype salicornia farms up to 250 hectares have been tried in Mexico, the United Arab Emirates and also in Saudi Arabia. Such plants should also be tried on experimental basis in Pakistan by using sea water.
The yields from salicornia equal or exceed the yields of soybeans and other oil seeds grown on fresh water. The researchers’ experience has shown that salicornia can thrive when the salinity of the water bathing its roots exceeds 100 parts per thousand-roughly three times the normal saltiness of the ocean.
It needs about 35 per cent more irrigation when grown using sea water than conventional crops raised with fresh water.
The agricultural scientists, therefore, need to focus on such plants. Their feasibility to thrive in Pakistan should be sensed and tested on experimental basis in collaboration with some international agencies with practical experience in line.
Fish culture: Fish culture is now being promoted in the country both at micro and macro levels. Big ponds act as evaporation tanks resulting in a considerable loss of water to atmosphere.
Substantive proportion of subsoil water is lost in filling these ponds. Sea water may be exploited for fish farming on larger scales in the barren lands of Sindh and Balochistan. This may save good quality sub-soil water for its higher productivity in crop production. However, proper selection of fish species may generate more income.
The government has implemented a number of projects with heavy investment on water supply, drainage and rehabilitation of irrigation infrastructure. It should, at the same time, invite the think tank for strategic planning on sea water farming in saline agriculture.
The establishment of a sea water-farming research institute at Karachi will help promote use of sea water. Our researchers must direct their efforts to sea water farming and making plant species genetically improved to withstand sea water problem.
No doubt, a prosper future can be granted to agriculture if we discover the economical use of brackish sea water for crop production.
These are only the hectic and the sincerest efforts of our dedicated scientists that after green revolution may impart a blue revolution to this country making it beautiful, prosperous and all green in future.