IN ORDER TO DETERMINE EFFECT OF WEED /CROP INTERFERENCE ON WEED CANOPY ARCHITECTURE AND SPRING BARLEY YIELD AS AFFECTED BY LONG-TERM CHEMICAL FERTILIZERS, AN EXPERIMENT WAS CONDUCTED IN LONG-TERM SITE AGRICULTURAL UNIVERSITY OF TIMIRIAZEV, MOSCOW, DURING 2004 AND 2005. THE TREATMENTS WERE N, P, K AND NPK APPLICATION AND CONTROL (WITHOUT FERTILIZER). ANALYSIS SHOWN IN PLOTS THAT RECEIVED N, P, AND K ALONE THAT WEED DENSITY WAS SIMILAR OR HIGHER THAN CONTROL. THE COMBINATION OF FERTILIZERS (NPK) DECREASED WEED DENSITY 2 TIMES. NITROGEN APPLICATION ALONE HAD INCREASED WEED DRY MASS AT THE TOP THIRD CANOPY STRATUM. IN THIS PLOTS WEED COVER WAS 67%, WHILE IN REST IT WAS LOWER THAN 22%. THE COMBINATION OF FERTILIZERS HAD INCREASED SPRING BARLEY YIELD.