EFFECT OF SELENIUM-ENRICHED CALCIUM NITRATE, TOP-DRESSED AT DIFFERENTGROWTH-STAGES, ON THE SELENIUM CONCENTRATION IN WHEAT

A greenhouse experiment was conducted to evaluate the effect of Se con tained in calcium nitrate, top-dressed at different growth stages, on the Se concentration in wheat (Triticum aestivum L.). Selenium as sodi um selenate was added to Ca (NO3)2 and NPK (21-4-10) during the manufa cturing process. A silty clay soil with soil pH of 6.1 was used. For s elenium treatments incorporated in Ca(NO3)2 were top-dressed at both t he tillering and heading growth stages at rates of 0, 15, 30, and 45 m g kg-1 of Ca(NO3)2 fertilizer equivalent to about 0, 0.003, 0.007, 0.0 1 mg Se kg-1 soil, respectively. A fifth treatment of 20 mg Se kg-1 of NPK (21-4-10%) equivalent to 0.007 mg Se kg-1 soil was basal dressed at the time of sowing. Calcium nitrate with or without Se was top-dres sed at the rate of 35 mg N kg-1. In addition all pots received a basal dose of N at the rate of 7 0 mg N kg-1 through a NPK(21-4-10) fertili zer. The Se-enriched Ca(NO3)2 increased the uptake and concentration o f Se in wheat significantly (rho>0.05) with increasing concentration o f Se in the fertilizer applied. The Se concentration in wheat grain in creased from <1.1 to 468 mug Se kg-1 in the first year when the concen tration in the Se-enriched Ca (NO3)2 was increased from 0 to 45 mg Se kg-1 but the corresponding increase in the second and third year was l ower. The Se concentration in the grain was more than twice of that in the straw. The uptake and concentration of Se in wheat, except in the second year, was generally higher when Se was top-dressed at heading as compared to that when it was top-dressed at tillering but the conce ntration differences between time of application were not statisticall y significant(rho>0.05). Basal application of Se-enriched NPK (0.007 m g Se kg-1 soil) was only half as effective as an equivalent rate of Se in top-dressed Seenriched Ca(NO3)2 in increasing the Se concentration in wheat and the concentration levels among these treatments were sig nificantly (rho>0.01) different. It was concluded that topdressing of Se-enriched Ca(NO3)2 at 30 mg Se kg-1 is an effective method of applic ation to increase the Se concentration in wheat grain to a level, > 10 0 mug kg-1 dry matter, considered adequate for human consumption.