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Two field experiments were conducted during successive seasons of 2008/2009 and 2009/2010 at Sakha Agricultural Research Station to study the effect of herbicides and urea as an additive to herbicides on wheat, NPK uptake, photosynthetic pigments and associated weeds. The results indicated that using the recommended rate of herbicides, (isoproturon + diflufenican) at 300g a.i./fed. for control total annual weeds, tribenuron-methyl at 6.0g a.i/fed. for control broad-leaved weeds and clodinafop propargyl at 21g a.i./fed for control grassy weeds as applied alone postemergence as well as hand weeding twice, gave excellent weed control (93.6, 68.0, 45.9 and 93.6 % ), respectively. While, the same herbicides when applied at moderate rate (isoproturon + diflufenican) at 244.5g a.i./fed, tribenuron-methyl at 4.5g a.i /fed and clodinafop propargyl at 15.75g a.i/fed) mixing with 1% urea increased the herbicides efficiency in controlling the annual weeds by about ( 90.2, 65.9 and 44.5 %). Mixing 1% urea with the same herbicides at low rate (isoproturon + diflufenican at 165g a.i/fed, tribenuron-methyl at 3.0g a.i/fed and clodinafop propargyl at 10.5g a.i/fed) gave poor weed control and were significantly less efficient than the other treatments at the first survey in the first season. Hand weeding treatment, (isoproturon + diflufenican), tribenuron-methyl and clodinafop propargyl at high rate, alone as post-emergence as well as the same herbicides at moderate rate plus 1% urea had higher efficiency in controlling annual weeds and increased the plant height, spike length, weight of grains/ spike, number of grains/spike, straw yield (ton/fed) and grains yield (Ardab/fed), compared with the other treatments used. All herbicidal treatments as well as hand weeding treatment increased protein, phosphors, potassium and carbohydrate percentages and their uptake kg/fed in wheat grains over control treatment. Data also, cleared that all herbicides treatments slightly decreased chlorophyll a, b and total chlorophyll and; increased carotene content. From results of correlation analysis the fresh weight of total weeds, grassy weeds and broad-leaved weeds biomass were negative correlated with wheat yield. Grassy weeds were more aggressive in their competitiveness effect than broad-leaved weeds on wheat yield and its components. These results indicated that under heavy infested with annual weeds, it is possible to apply herbicides i.e.(isoproturon + diflufenican) for annual weeds control, tribenuronmethyl for broad-leaved weeds control and clodinafop propargyl for grassy weeds control at high rate alone or same herbicides at moderate rates mixed with 1% urea. These findings revealed obviously that such weed control measure can minimize weed /wheat competition and consequently gave the highest reduction in weeds and increase wheat yield and its components.

EFFECT OF HERBICIDES AND UREA AS ADDITIVE ON WHEAT, NUTRIENT UPTAKE, PHOTOSYNTHETIC PIGMENTS AND ASSOCIATED WEEDS