A steady and progressive increase in rapeseed yield was observed with each increment in applied nitrogen rates up to 213 kg/ha in both seasons. As for nitrogen application times, the analyzed data showed that adding a split dose (either 1/2 or 1/3) before the third irrigation was a common part between high yielding treatments in 1985/86 season. Nitrogen rates X application times interaction affected rapeseed yield significantly during the first winter season. The highest seed yield of 2.5 t/ha was obtained by adding 213 kg N/ha in two split doses at sowing and just before the third irrigation. The second yield value of 2.47 t/ha was produced under the same N rate when applied in two split doses before second and third irrigation. However, in the second season (1986/87), rapeseed plants did not exhibit significant responses to nitrogen rates X application times interaction. Chemical analyses showed that rapeseed oil content and its fatty acids (Palmetic, Stearic, Oleic, Linoleic, Linolenic, Arachidic and Erucic) percentages were not significantly affected by either nitrogen rates or application times in both seasons. A very low content of Erucic acid (0.1–0.9 %) in all tested sample was noticed.

The present investigation was conducted to determine the critical period of weed competition in soybeans at Giza, Egypt. Weed flora in the experimental site at Giza contained a wide range of species during both seasons of study (1990 and 1991). Total weed dry weight increased progressively with time up to 12 WAE (182.0 g/m2). Weed‐free and weedy periods exhibited significant effects on soybeans height, number of pods per plant, stand at harvest, biological and seed yields. Optimum seed yields were produced by weed‐free durations for 6 WAF up to all season (3.229–3.545 t/ha). Whereas, weedy periods for 2, 4, 6, 8, 10 and 12 WAF reduced seed yield by 14.9, 28.0, 35.3, 45.1, 48.1 and 51.1 %, respectively. Weed competition for the entire season caused 56.1 % reduction in soybean seed yield. The obtained results indicate that weed competition during the early stages of growth, adversely affected soybeans. At least 6 WAE of weed‐free period was required to insure optimum soybean growth and yield. However, oil and protein contents were not affected by weed competition.

Field experiments showed that superior control of the existing weed flora was obtained by applying: alachlor + linuron, alachlor + chloramben and cyanazine. Herbicidal treatments of alachlor, trifluralin, prometryn and oxadiazon were highly effective in controlling dominant weed species. Some herbicidal treatments produced sunflowers with larger head diameter as compared to unweeded check. As a result of suppressed weed interference, alachlor in combination with linuron or chloramben and cyanazine accounted for the highest seed yield values in 1985 and 1986. Chemical analyses exhibited that sunflower oil content was not affected by weed control applications. Furthermore, oil constituents (oleic, linoleic, steric and palmitic fatty acids) expressed insignificant responses to applied treatments.

Two field experiments were conducted at the Experimental station, Faculty of Agriculture, Cairo University, Giza, Egypt in 2005/2006 and 2006/2007 to study the effect of critical periods of weed competition on Faba bean (Vicia faba L). The experiment consisted of two planting systems one side and both of sides on the ridge with ten treatments: weed-free and weedy periods for three weeks, six, nine, and twelve and the all season. Dominant weed species were weed beet (Beta vulgaris L.), Black mustard (Brassica nigra L.), chicory (cichorium pumilum L.), spring sowthistle (Sonchus olereacus L.), and wild oat (Avena fatua L.) Results indicated that weed removal even once after faba bean emergence substantially reduced the growth of annual broadleaf and grassy weeds after 60 days from sowing and at harvest as compared to weedy throughout all the growing season. But , the most effective treatments were when broadleaved or grassy weeds allowed to grow for 3 or 6 weeks after sowing, recording the highest weed depression values (>70%). In the second order, the allowing weeds to grow for whole growing season markedly decreased seed yield per plant and feddan than when weeds were removed after 6 or more. Also, seed yield was improved by shortening the period of crop-weed interference through keeping the field free from weeds for the whole season or for 9-12 weeks. (75-78 % in seed yield /feddan over the unweeded and 97.2-98.6% during the first and second seasons respectively). However, sowing faba bean on both sides of the ridge produced higher seed yield per feddan, but the differences did not reach the significance level. Sowing on both side of the ridge reduced fresh weight of both of broadleaves and grasses weeds. However, there were different effects of periods of weed removal importance of based on when it was initiated, being more effective if it was early. Thus, demonstrating that weed interference against faba bean in the early growth periods. Seed yield was reduced from 1.5T/fed. for weed free to 0.5 T/fed. for the weedy treatments. There was a slight difference in the yield between 3 and 6 weeks weed-free periods. However there were insignificant differences between weeds free periods. The critical weed-free period was defined as to prevent yield losses greater than 5% and the critical weed free period was estimated by 40 to 50 days.