NITRATE EFFECTS ON PREEMERGENCE GROWTH AND EMERGENCE PERCENTAGE OF WHEAT (TRITICUM-AESTIVUM L) FROM DIFFERENT SOWING DEPTHS

The effects of a range of applied nitrate (NO3-) concentrations (0-20 mol m-3) on germination and emergence percentage of Triticum aestivum L. cv. Otane were examined at 30, 60, 90 and 120 mm sowing depths. Germination percentage was not affected by either sowing depth or applied NO3- concentration whereas emergence percentage decreased with increased sowing depth regardless of applied NO3- concentration. Nitrate did not affect emergence percentage at 30 mm sowing depth, but at 60 to 120 mm depth, emergence percentage decreased sharply with an increased applied NO3- concentration of 0 to 1.0 mol m-3 then decreased only slightly with further increases in applied NO3- of about 5.0 mol m-3. Root and shoot growth, NO3- accumulation and nitrate reductase activity (NRA) of plants supplied with 0, 1.0 and 10 mol m-3 NO3- at a sowing depth of 60 mm were measured prior to emergence. The coleoptile of all seedlings opened within the substrate. Prior to emergence from the substrate, shoot extension growth was unaffected by additional NO3- but shoot fr. wt. and dry wt. were both greater at 1.0 and 10 mol m-3 NO3- than with zero NO3-. Root dry wt. was unaffected by NO3-. Nitrate concentration and NRA in root and shoot were always low without NO3-. At 1.0 and 10 mol m-3 NO3-, NO3- accumulated in the root and shoot to concentrations substantially greater than that applied and caused the induction of NRA. Regardless of the applied NO3- concentration, seedlings which failed to emerge still had substantial seed reserves one month after planting. Coleoptile length was substantially less for seedlings which did not emerge than for seedlings which emerged, but was not affected by NO3-. It is proposed that (a) decreased emergence percentage with increased sowing depth was due to the emergence of leaf 1 from the coleoptile within the substrate and (b) decreased emergence percentage with additional NO3- was due to the increased expansion of leaf 1 within the substrate resulting in greater folding and damage of the leaf.