Weeding and nitrogen effects on farmers' wheat crops in semi‐arid Morocco

Summary The effects of three weeding systems with and without top‐dressed nitrogen were examined in 40 experiments on bread wheat and durum wheat planted by farmers in the Chaouia (semi‐arid area of Morocco) in 1984–1985 and 1985–1986 growing seasons. In both years, hand‐weeding to simulate collection of forage reduced weed numbers by 30% and removed 63% of the weed dry weight. Treatment with 2, 4‐D removed 66% of the weeds and reduced weed dry weight by 82%, in 1985–1986. Hand‐weeding for forage produced 427 kg ha −1 weed dry matter in both years, but wheat grain yields were 179 kg ha −1 lower than with 2.4‐D treatments. Over both years, the cost of each kg weed forage was 0·43 kg grain yield loss. Without weeding grain yields were 130 kg ha −1 lower than 2, 4‐D treatments. Weed control with 2,4‐D increased wheat grain yields over both non‐weeded and hand‐weeded treatments by an average of 154 kg ha −1 . Overall, there were no significant effects of nitrogen on wheat or weed yields nor interactions between top‐dressed nitrogen and weeding systems. A total of 157 weed species belonging to 29 botanical families were identified on the 40 experimental sites over both years; 89% were dicotyledons. Papaver rhoeas L. (common poppy), 2, 4‐D susceptible plant, was the most annual weed in wheat fields in Chaouia.