Studies On Weed Competition And Performance Of Various Herbicides Under Different Sowing Dates And Nitrogen Levels In Rainfed Cotton (Gossypium Hirsutum L.)
Two field experiments were carried out at the University Farm, Samaru, Zaria, in the northern guinea savanna zone during 1981 wet season. Experiment I referred as “weed competition study” consisted of two main plot treatments of sowing time (June-sowing and July-sowing) and 12 subplot treatments of duration of weed competition, among which six consisted of weed-free period of two weeks interval up to harvest and six of weed-infested period of two weeks interval up to harvest. Nitrogen at the rate of 30 kg N ha was applied by side dressing to the cotton crop at three weeks after sowing. Experiment II named as “weed control study”, consisted of two treatments of June and July-sown cotton superimposed with three treatments of 0, 30 and 60 kg N ha and thereby constituting six main-plot treatments; and six sub-plot treatments of weed control v/here four treatments of herbicide mixtures of fluridone plus diuron @ 0.4+0.4 and 0.8+0.8 kg a.i. and norflurazon plus diuron @ 0.4+ 0.4 and 0.8 + 0.8 kg a.i. ha-1 were compared with hoe-weeding and unweeded check. All herbicide treatments were applied pre-emergence, one day after sowing. Cotton sown on 29 June and 21 July, 1981 (referred as June-sown and July-sown crop). Spray application of “Cymbush” to the cotton crop at the rate of 2.5 1 ha to control insect-pests, was made from 10 weeks to 16 weeks after sowing. Manual picking of the seed-cotton started at 22 weeks after sowing, and continued for five weeks. June-sown cotton outyielded that sown in July by 48 per cent in weed competition study. The most critical period of weed competition was four to six weeks after sowing in June-sown and two to six weeks in July-sown cotton. Weed dry matter production had a negative correlation co-efficient with growth, yield and yield components of cotton. In weed control studies seed cotton yield was not significantly affected by time of sowing. Cotton crop responded well to 60 kg N ha-1 in June-sown crop and to 30 kg N ha to July-sown crop. The most promising herbicide treatment was fluridone plus diuron at 0.8 + 0.8 kg a.i. ha-1 . At 60 kg N ha-1 an increased susceptibility of weeds to fluridone plus diuron at 0.8+ i.8 kg a.i. ha was observed as judged by a drastic reduction in weed dry matter. Fluridone plus diuron at high rate (0.8 + t.8 kg a.i, ha ) in June-sown cotton under 30 and 60 kg N ha was the best herbicide ond’was-similarly effective under 60 kg N ha in July-sown crop.