SUMMARY

There are many different methods which have been world wide used to determine the duration of some corn phenophase. The most reliable method is the sum of heating units (GDU – Growing deegre unit – sum of the effective temperatures). In the experiment which has been carried out with four different kinds of hybrids, the duration of some corn phenophase was being monitored togethen with the duration of whole period of vegetation by number of days and sum of effective temperatures method. It was olso shown in the experiment that there was dependence of duration of some corn phenophass on the dail air temperature expressed by the coefficient of correlation and linear regression. The researsh results show that hybrids with longer vegetation have larger number of days as well as larger sums of effective temperatures. It's determined that there is an important link between the temperatures hight and the duration of some corn phenophases. Weak correlative connection is determined of phenophase shooting – 11 leaf and phenophase 11 leaf – silking. At corn silking phenophase fuul ripened strong correlation was determined betwen medium air temperatures and duration of this phenophase (r = 0.72-0.90). It is especially important to emphasize the sum of effective temperatures for some hybrids which can be used for areation of corn hybrids, to which a greot deol of attention has been given lately.

          Key words: hybrids, phenophase, air temperatures, the sum of effective temperatures, rauonization.