Salinity is a growing problem for farmers worldwide. The UN Food and Agriculture Organization (FAO) in Rome estimates that more than 700 million hectares of the world's soil- an area which would cover about two-thirds of the US- are poisoned either by salt itself or by other forms of sodium (see Graph).
On arable land, much of the problem is of farmers' own making, because they spray their crops with poor-quality, salty water. The FAO estimates that 20 per cent of irrigated farmland is now choked with salt, plus 2 per cent of non-irrigated land. In an effort to keep this land productive, researchers are attempting to develop new strains of crops that survive in salty soil.
But saltwort may provide an alternative. Also known as beachwort, this salt-loving halophyte colonises salt marshes throughout the Americas, where it grows up to 2 metres tall. An analysis of its peppercorn-sized seeds by Massimo Marcone of the Ontario Agricultural College at the University of Guelph has revealed that they are packed with nutritious proteins, oils and starches.
As saltwort is a perennial, it continues to produce seeds every year. And harvesting the seeds is simple: you just shake the bush. It could potentially be a highly productive crop.
Marcone's analysis showed that protein accounts for about 17 per cent of the saltwort seeds' weight, and that the seed is rich in the amino acids lysine and methionine. A quarter of its weight is accounted for by oils that are 93 per cent unsaturated, and so less likely to cause heart disease. The oil is almost identical to safflower oil, which is used for cooking and in salad dressings, as well as for making margarine. The seeds also contain beneficial antioxidants such as tocopherols, which are thought to fight cancer. Starch makes up more than half the seeds' weight, Marcone found. This could be used for purposes other than food, including cosmetics, paper coatings, printing inks and biodegradable plastics.
So would saltwort find a place in the recipe books? "The seeds are extremely edible and taste nutty," says Marcone. "You could add them to salads, toast them or even make them into miniature popcorn," he says.
Besides providing potentially valuable harvests, he now plans to test whether saltwort sucks salt from the soil, possibly allowing ordinary crops to grow there again. His findings will be published in a forthcoming edition of the journal Food Research International. But even if saltwort does extract salt from soil, some specialists in contaminated land doubt whether the plant could return an over-salty crop field to normal all on its own. "It's not a substitute for full reclamation, which can cost $3000 per hectare," says Hassan Habhan, an expert in land management and conservation at the FAO.
Standard reclamation techniques involve undertaking operations like leaching, drainage, crop rotation and the addition of organic matter. On the plus side, Habhan agrees that growing salt-loving plants on otherwise barren land would be a good start. Not only does it have the potential to provide forage for animals, but also other materials based on the useful proteins, oil and starches that have been found in the saltwort seeds. "But a halophyte alone can't solve the problem of salt-affected soil," he warns.
By Andy Coghlan
New Scientist issue: 25th September 2002
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