INFLUENCE OF CROP ROTATION UPON WEED DEVELOPMENT ON CORN, WHEAT AND SOYBEAN CROPS

In every type of culture or group of cultures we can observe specific weeds. These weeds are adapted to the particular biological characteristics of the cultivated plant and at the specific technological issues. Monoculture or short crop rotations fulfill this mentioned above conditions for a longer period of time infesting the soil with weed seeds. On the other hand, long crop rotation leads to a proper development of technological changes for each type of crops. This aspect is obvious at corn and soy bean where the crop rotation for two years leads to a weed development of 110-116% compared with the four year crop rotation. The differences are reduced at the three year crop rotation, with a weed development level of 13-64% higher compared with the four year crop rotation. In the four year crop rotation compared with the two year one, the structure of weed development on the wheat culture involves significant modifications. The frequency of the following weeds was reduced: Centaurea, Adonis, Thlaspi, Sinapis, Vicia, Viola, Matricaria, Galeopsis Si Raphanus. On the other hand, the intensity of appearance with perennial weeds is: Agropyron repens, Cirsium arvense, Convolvulus arvensis and Symphitium officinale.