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At low concentrations selenium protects plants from oxidative stress. The nutrient increases the antioxidative capacity of plants and can have growth-promoting effects on senescing plants. So far the antioxidative properties of selenium are reported from bitter gourd, fenugreek, lettuce, mung bean, potato, rape, ryegrass, soybean, strawberry and wheat. Since the experiments concerned are conducted in a glasshouse or a laboratory, it is still unknown to what extent the beneficial role of selenium will be evident under field circumstances. At higher doses however selenium is harmful to plants.
Crop protection
Selenium protects plants against insect damage. Selenium containing substances in leaves and stems act as repellents, so that aphids, caterpillars and spider mites avoid these plants. Even in small amounts these substances are also toxic for these pests. American scientists have discovered this in experiments with alfalfa and cruciferous crops. From experiments with Indian mustard it appears that application of selenium can enhance resistance to fungal diseases. The researchers also found a snail species that prefers selenium rich parts of plants.
Soil and plant nutrition
Toxic effects on plants are well-known from soils with a high selenium status. Acid or neutral soils are mostly lower in plant available selenium than alkaline soils. In Finland, soils are very low in plant available selenium. Since 1984 Finnish NPK fertilisers have been supplemented with sodium selenate in order to improve the nutritional value of feed and foodstuffs. Also in other selenium deficient regions, farmers apply selenate to their crops. Some plant breeders already launched cultivars of food crops with an increased selenium content.
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