The study was carried out to analyze the spatial distribution of weeds in grain-grass-row crop rotation in the Northwestern region of the Russian Federation. Based on calculations of the index of pairwise species similarity and of the commonality coefficient of specific abundance, we revealed, on the one hand, a high similarity in the species composition of weeds within the studied crop rotation (0.81–0.94) and, on the other hand, significant differences in the structure of weediness of fields (30.4–70.6). The differences in weediness between some fields, both in terms of the number and the above-ground mass of weeds, turned out to be statistically significant. Species abundance varied within six–ten species/m2, numerical composition was within 150–312 plants/m2, and the range of phytomass was 51.2–272.5 g/m2 with the means for crop rotation fields of eight species/m2, 251 plant/m2, and 161.7 g/m2, respectively. Uneven or aggregated distribution of weeds on the crop rotation territory confirmed by high 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 in digital maps compiled, using special programs. Significant differences in the weed structure of crop rotation fields and in the distribution of individual weed species were a consequence of differences in the agrochemical characteristics of the soil, primarily in the acidity, the amount of exchangeable bases, and the organic matter content. When using herbicides in crop rotation, it is necessary to take into account individual characteristics of weediness in each field and the spatial distribution of mass species of weeds formed under the influence of long-term agricultural use.
Shpanev et al. (Mon,) studied this question.