EFFECT OF N-LEVEL AND ITS TIME OF APPLICATION ON YIELD AND NITROGEN UPTAKE OF SOME RICE ARIETIES

Two field experiments were carried out at Al-Khadmia, Kafr El-Sheikh Govemorate, during the two growing seasons of 1988 and 1989 to study the effect of five nitrogen levels (0, 20, 40, 60 and 80 kg N/ fed.) and three times of application (1/2 of N in dry soil + 1/2 of N at 20 days "AT", 1/2 of N at 20 days "AT" + 1/2 of N at "Pl" and 1/3 of N at 20 days "AT" + 2/3 of N at "PI") on yield and nitrogen uptake of two rice varieties namely Giza 181 and Giza 175. The results could be summarized as follows: In both seasons, Giza 181 exceeded Giza 175 in grain yield, straw yield, nitrogen uptake, nitrogen efficiency % and nitrogen recov­ery. Adding nitrogen as 1/2 of N in dry soil + 1/2 of N at 20 days "AT" significantly increased grain yield, straw yield,nitrogen uptake, nitrogen efficiency % and nitrogen recovery. Also, nitrogen levels increased grain yield, straw yield and total nitrogen uptake, while nitrogen efficiency % and nitrogen recovery tended to decrease with increasing N-levels. The interaction between rice varieties and time of N-application significantly affected grain yield. Giza 181 recorded the highest grain yield when nitrogen was added as 1/2 of N in dry soil + 1/2 of N at 20 days "AT". Also, adding 60 kg N/fed. in two equal portions, 1/2 of N at 20 days "AT" + 1/2 of N at "PI" for Giza 181 obtained the highest value of total N-uptake. On the other hand, Giza 181 gave the highest grain yield by adding 60 kg N/fed. as 1/2 of N in dry soil + 1/2 of N at 20 days "AT".