STUDIES ON THE UTILIZATION OF LATE-SEASON APPLIED FERTILIZER NITROGENIN-FIELD AND MODEL EXPERIMENTS WITH WINTER-WHEAT

The utilization of nitrogen (N-15)-fertilizer was studied with winter wheat grown under field conditions and in a model experiment using lar ge pots (70 kg soil pot(-1)). Fertilizer N (160 kg ha(-1), 2 g pot(-1) ) was applied in two or three different doses timed in the period betw een the beginning of tillering and that of flowering in both experimen ts. The field experiment contained also a fall N timing treatment. Bot h experiments were carried out with the same soil type and wheat varie ty. The N content of the tested plant parts (rachis, glumes, flag-leaf blade, flag-leaf sheath, upper most internode, and lower plant part) was found to be the highest in treatments including the fall applied o r early spring N doses. Eighty-eight percent of the N detected in the uppermost internode depleted during the period between 72% grain moist ure content and full ripening. It is concluded that besides the upperm ost internode and flag-leaf, the glumes, as potential N sources, may a lso play an important role in the N translocation into the grains. The wheat plants grown in pots and watered were able to incorporate into the grains about 50% of the late N doses even though distributed at fl owering. The favorable effect of late-season N application, however, c ould not be statistically proved. Under field condition, the grains co uld not utilize the late applied N doses and there could not be detect ed any favorable effect of late-season N application either in the exp erimental year, which was very rainless especially in the period most important from the point of view of grain development.