Abstract:
A field experiment was conducted during 1994 and 1995 wet season on the research farm of the Institute for Agricultural Research, Samaru (11’11’ N , 07°E 680m) located in northern Guinea savanna agro-ecological zone of Nigeria. The main objective was to investigate the effect of nitrogen level and period of weed interference on maize/rice mixture. The treatments consisted of three levels of nitrogen (0, 60 and 120kg/ha) and ten period of weed interference (weed free for 3,6,9, 12WAS and harvest and weed infested for the same period) . The treatment were laid out in a split plot design with nitrogen in the main plot and period of weed interference in the sub plots. The result of this study revealed that increasing nitrogen from 0 to 120kg\ha significantly increased grain yield of maize up to the maximum of 2243 kg/ha and 3809 kg/ha in 1995 and 1995 respectively in treatments that were kept weed-free until 6,9,12WAS and harvest and those initially weed-infested for the first 3WAS. On the other hand, nitrogen application did not increase the grain yields of maize on the plots weed-infested until harvest and those kept weed-free initially for 3WAS. For rice, increasing nitrogen from 0 to 120kg/ha significantly increased grain yield up to the maximum of 933 and 1216 kg/ha in 1994 and 1995 respectively in treatments that were kept weed-free until 6,9,12 WAS and harvest. Nitrogen application did not increase the grain yield of rice on the plots that were kept weed-free initially for 3WAS in both years and those weed-infested for 9WAS and more in 1995. As compared with the crops kept weed-free throughout the lifecycle, uncontrolled weed growth resulted in 83.03% and 93.85% reduction in average grain yield for both years in maize and rice respectively. The critical period of weed interference in maize and rice mixture was established to be between 6 and 9WAS for maize and 5 and 9WAS for rice. There was negative correlation between the maize grain yield and cumulative weed dry matter production (r=-0.028, r= -0.20 in 1994 and 1995 respectively) as well as weed cover scores (r= -0.33, r= -0.21 in 1994 and 1995 respectively). Rice grain yield was also negatively correlated with cumulative weed dry matter production (r= -0.20, r= -0.52 in 1994 and 1995 respectively) as well as weed cover scores (r= – 0.21, r = -0.46 in 1994 and 1995 respectively). Other plant characters for maize and rice were highly positively correlated with the grain yield.
EFFECT OF NITROGEN AND PERIOD OF WEED INTERFERENCE ON MAIZE/RICE MIXTURE
