The paper presents a field experiment model to investigate the competition between the crop and weeds in agrophytocenosis. Indicators were proposed to be used to evaluate the effects of these interactions. The indicators are based on the relative differences in the number of individuals, amount of biomass and the value of biometric characters of the plants, thus allowing us to define and to compare the reactions of the crop to weed infestation, reactions of respective weed species and weed communities to the competition from the crop and to evaluate the competition between the crop and weeds in a given agrophytocenosis. The method of defining respective indicators of competitive effects makes it possible to compare these effects in different species, at different development stages and for different plant organs.

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