The uptake of applied selenium by agricultural plants

Summary Elemental selenium and a series of selenites and selenates were applied in pot and field experiments. With the elemental selenium a small increase in concentration in the plants was found in both kinds of experiments with red clover, lucerne, mustard, andsugar beet as test plants, but not with barley. In the second year an increase in the concentration in the plants was found in lucerne only (field experiment). In a pot experiment eight successive cuts of clover all had nearly the same content. All the selenites had the same effect on the concentration in the plants, and the concentration in the eight cuts of clover decreased with time at the same rate for all six selenites irrespective of solubility. The decrease was about a factor of six. In the field the effect of K₂SeO₃ in the second year was reduced by 50 to 80 per cent. Also the selenates gave the same concentration in plants independently of the solubility. But the concentration was 20–50 times that obtained with selenites, and the decrease in the effect with time was greater. In the eight clover cuts the effect of selenate decreased four times as much as the effect of selenite. In the field the effect of K₂SeO₄ decreased more from the first to the second year than the effect of BaSeO₄. During a two years field experiment with mustard the total uptake as a percentage of the added selenium was 0.01% of Se°, 4% of K₂SeO₃ and 30% of K₂SeO₄ and BaSeO₄. With lucerne, barley and sugar beet the uptake was one third of this or less. Determinations of water-extractable selenium in profiles from the field in the autumn showed no increase succeeding the addition of K₂SeO₄ in the spring while the addition of BaSeO₄ increased the extractable amount in both autumns. Addition of five times more selenite increased the water-extractable as well as the total soil selenium in the upper 25 cm, and the increase in total Se was also present in the second autumn.