Silicon does not alleviate the adverse effects of drought stress in soybean plants

Beneficial effects of silicon (Si) in the plants growth under conditions of drought stress have been associated with to uptake and accumulation ability of element by different species. However, the effects of Si on soybean under water stress are still incipient and inconclusive. This study investigated the effect of Si application as a way to confer greater soybean tolerance to drought stress. The experiment was carried out in 20-L pots under greenhouse conditions. Treatments were arranged in a randomized block design in a 2 x 4 factorial: two water regimes (no stress or water stress) and four Si rates (0, 50, 100 and 200 mg kg(-1)). Soybean plants were grown until beginning flowering (R1) growth stage with soil moisture content near at the field capacity, and then it started the differentiation of treatments under drought by the suspension of water supply. Changes in relative water content (RWC) in leaf, electrolyte leakage from cells, peroxidase activity, plant nutrition and growth were measured after 7 days of drought stress and 3 days recovery. The RWC in soybean leaves decreased with Si rates in the soil. Silicon supply in soil with average content of this element, reduced dry matter production of soybean under well-irrigated conditions and caused no effect on dry matter under drought stress. The nitrogen uptake by soybean plants is reduced with the Si application under drought stress. The results indicated that the Si application stimulated the defense mechanisms of soybean plants, but was not sufficient to mitigate the negative effects of drought stress on the RWC and dry matter production.