YIELD AND ITS ATTRIBUTES OF TWO MAIZE CULTIVARS AND ASSOCIATED WEEDS AS AFFECTED BY SOME WEED CONTROL METHODS AND NITROGEN FERTILIZER LEVELS

These experiments were performed for two successive summer seasons of 2013 and 2014 at Gemmeiza Agric. Res. Station, Gharbia Governorate, Egypt. The ultimate aim of this work was to evaluate the effect of four weed control methods [1- un-weeded check W_1,, 2- hand hoeing twice at 18 and 30 days age W_2,, 3- using Harness herbicide (Acetochlor) 84% Ec at the rate of one liter/fad., sprayed directly after planting and before irrigation,W₃ and at last_, 4- using Harness herbicide 84% Ec plus one hand hoeing conducted at 30 days old W₄], three nitrogen levels, viz: 90, 120 and 150 kg N/fad., and their interactions on the yield, its attributes, quality of the two maize cultivars, being: 1- white cultivar SC 128 and 2- yellow cultivar SC 168 as well as on the associated weeds. The experimental design was a split-split plot system of three replicates. The obtained results indicated that the four weed control treatments exhibited significant variations in most of the studied characters for both weeds and maize, where the W₄ treatment (using Harness herbicide 84% Ec plus one hand hoeing) produced markedly greater mean averages in each of: weed reduction percentage, maize plant and ear heights, ear length and diameter, number of rows / ear, number of grains/row, grain index, shelling percentage, grain yield / fad, protein content and yield / fad., when compared with W₃, W₂ and the un-weeded check, orderly. But, opposite trend was seen regarding the total weed dry weight (g/m²), since the un–weeded check was extreme in this regard. Such inclination was clearly manifest in both seasons and over them too. Also, SC 128 maize cultivar was significantly superior to its counterpart SC 168 in all yield attributes and yield/fad., in both trials and across them as well and vice versa regarding the total weed dry weight (g/m²). In addition, the three N levels tested gave significant changes in all the studied traits for both weeds and maize, where the highest N level of 150 kg N/fad was most effective in enhancing such tested characters  (except the total weed dry weight in g/m²) if compared with both 90 and 120 kg N levels/fad. Grain yield/fad., of maize correlated positively and strongly with each of: plant and ear heights, ear length and diameter, rows/ear, grains/row, 100- grain weight, shelling and protein percentages, but weed biomass gave negative and significant relations with grain yield/fad. Such correlation results referred significantly to the effective treatments tested in this study to suppress the competitive ability of weeds and maize grain yield enhancement. Based on this research findings, keeping maize field weed-free by using Harness herbicide (Acedochlor) 84% Ec pre-emergence at the rate of one liter/fad., plus one hand hoeing at 30 days old to control the spread weeds either broad– leaved or grassy as well as adding the appreciable N level of 150 kg N/ fad, especially in low deficient N soil, could be taken into account in depressing the domenant competitive weeds and maximizing the final yields/fad., from grain and protein for the SC 128 cultivar under Gemmeiza location conditions, Gharbia Governorate, Egypt.