Effect of Selenium and Sulphur Compounds on the Growth and Chemical Composition of Forage Cowpea

The effects of selenium and sulphur sources were studied in green-house on forage cowpea (var. FOS-l). The growth of cowpea was depressed and dry-matter yield decreased with the application of selenium up to 5 ppm, whereas the application of sulphur at 25 and 50 ppm generally increased the dry-matter yield. Sources of sulphur, i.e., BaSO₄, CaSO₄.2H₂O, (NH₄)₂SO₄, and K₂SO₄ did not show much difference among themselves although BaSO₄ and CaSO₄.2H₂O were less soluble than K₂SO₄ and (NH₄)SO₄. The concentration of selenium increased with the increase in selenium application and decreased with the application of sulphur salts in all the cases. The sulphur concentration and uptake increased with the application of sulphur salts. The selenium application decreased the sulphur concentration and uptake in plants. The phosphorus concentration and uptake increased with 2.5 ppm selenium but decreased with 5 ppm in absence of added S but in presence of sulphur salts phosphorus decreased with increasing selenium application. Application of sulphur generally increased phosphorus.

Cystine was found to be in higher concentration than cysteine. Both these amino-acids decreased with the application of selenium, but increased with the application of sulphur. The least soluble salts of sulphur, i.e., BaSO₄.CaSO₄.2H₂O were as effective as any other salt.