SPATIAL STRUCTURE OF WEED CONTENSION OF GRAIN-GRASS-ROW CROP ROTATION IN THE NORTH-WEST OF RUSSIA

The study was carried out to analyze the spatial distribution of weeds in grain-grass-row crop rotation in the North-West region of the Russian Federation. Based on calculations of the index of pairwise species similarity and the coefficient of commonality of specific abundance, it was revealed, on the one hand, a high similarity in the species composition of weeds within the studied crop rotation (0.81...0.94), on the other hand, significant differences in the structure of weediness in fields (30, 4…70.6). The differences in weediness between some fields, both in terms of the number and above-ground mass of weeds, turned out to be statistically significant. Species abundance varied within 6...10 species/m2, numerical composition - 150...312 specimens/m2, phytomass - 51.2...272.5 g/m2 with an average value of this indicator for crop rotation fields of 8 species/m2, 251 ind./m2 and 161.7 g/m2, respectively. Uneven or aggregated distribution in the crop rotation territory, confirmed by high values of the coefficients of variation (151...567) and aggregation (2.1...16.2), turned out to be characteristic of all widespread species of weeds. Geostatic features of the distribution of their mass species in the area of grain-grass-row crop rotation were quite clearly visible on digital maps compiled using special programs. Significant differences in the weed structure of crop rotation fields and the distribution of individual weed species were a consequence of differences in the agrochemical characteristics of the soil, primarily acidity, the amount of exchangeable bases and the content of organic matter. When using herbicides in crop rotation, it is necessary to take into account the individual characteristics of weediness in each field and the spatial distribution of mass species of weeds, which have developed under the influence of long-term agricultural use.