Abstract:

Weed communities are classified with the quantitative analysis so as to avoid some possible subjective factors in the classification, description and distribution of weed communities; therefore, it is possible in this way to make the study comprehensively, objectively and quantitatively.

In summer crop fields of river valleys and hilly lands of Anhui Province, 74 sampling fields were chosen to take 10 sampling plots, i.e. 10 plots were randomly selected from these fields. Transformed into overall values, the data collected by eyesight of weed damages to crops in seven scales were analysed with the fuzzy cluster. On the basis of ecological factors and community features of the sampling sites, the degree of confidence was selected and the sampling sites were classified into various clusters. The result showed that the distribution o[ weed communities in rape and wheat fields of the said areas is restrictly influenced by crop rotation systems and soil types. The distribution pattern of weed communities was described as follows, the Cerastium viscosum + Veronica persica association is in the grey muddy soil dry lands of the rotation of wheat (or rape) and cotton; the Galium aparine var. tenterum+Avena fatua association, in the yellow-red earth or yellow-brown earth dry lands of the rotation of wheat and sweet potato (or soybean or cotton); the Alopecurus aequalis association, in the rice soil fields of the rotation of rape and rice. In order to evaluate the weed damage degree to a crop in a type of weed community, the overall weed damage index (OWDI) was first developed. As a result, the worst weeds in the fields of different crop rotation systems and soil types were determined quantitatively in accordance with this index. Finally, the strategy for integrated control of the worst weeds was suggested.

The formula of the overall value and the overall weed damage index (OWDI) is

Overall Value=Σ (Number of a scale′s· Value of the scale occupying fields)/50

OWDI =Σ(Number of a scale′s occuppying·Value or the scale fields)/ Total number of fields of weed community cluster·Value of the highest scale