The effects of forms of selenium on the accumulation of sulfur, selenium, and forms of nitrogen and phosphorus in cowpea (Vigna sinensis) were studied in pots in the greenhouse at Haryana Agricultural University, Hissar, India. The soil used was sandy, and forms of selenium added were Na2SeO4 · 10H2O, Na2SeO3 · 5H2O, H2SeO3, and elemental selenium at the rate of 0, 1, 2.5, and 5 ppm. Dry matter yield and sulfur content decreased with increased selenium application. This inhibition in plants, attributable to applied selenium, was in the order SeO4 > H2SeO3 > SeO3 > elemental selenium. Plant selenium increased with increasing application of all forms of selenium. The highest plant selenium (11.58 ppm) was in the plants treated with SeO4, followed by the plants treated with H2SeO3, SeO3, and elemental selenium. The total plant phosphorus increased with increased selenium application in any form, but maximum phosphorus occurred in SeO3-treated plants. The inorganic phosphorus increased similarly, the largest amount occurring in SeO4-treated plants. Organic phosphorus decreased with selenium application; minimum concentration was recorded in SeO4-treated plants.
Soluble nitrogen decreased, relative to the control, with applications of 2.5 and 5 ppm selenium. This decrease was minimal for elemental selenium and maximum for SeO4. Soluble nitrogen, in the case of SeO3 was higher than for H2SeO3. Total plant nitrogen and protein also decreased. Amino N, amide N, and ammoniacal and nitrate N increased, compared to the control. The largest amount of all these forms was noted in SeO4-treated plants. Overall, among the forms of selenium normally reported in soils, the SeO4 form showed the highest inhibition, whereas SeO3 showed less than both SeO4 and H2SeO3.