Weed species diversity and community composition in conventional and organic farming: a five-year experiment.

Abstract

aim of this investigation was to study the influence of organic (ORGFYM - organic with green and cattle manure, ORGGRM - organic with green manure) and conventional (CONFYM - with green manure, cattle manure, mineral fertilizers and pesticides) treatments on weed species diversity, their abundance and biomass. A total of 44 weed species/taxa were encountered during the study covering a period of 2007-2011. In the ORGGRM, the number of weed species was 39 (24 annuals and 15 perennials), in the ORGFYM - 36 (21 annuals, 1 biennial and 14 perennials) and in the CONFYM treatment - 30 (19 annuals, 1 biennial and 10 perennials). Centaurea cyanus, Cerastium arvense, Geranium pratense, Myosurus minimus, Polygonum laphatifolia, Plantago lanceolata and Plantago major were found only in ORGGRM treatment. The average number of species per 0.25 m 2 was 9.2 and 9.3 in the organic treatments and 4.9 in the conventional treatment. The average values of Shannon diversity index were statistically higher in the organic (ORGGRM - 1.70, ORGFYM - 1.65) than in the CONFYM (1.06; p < 0.05) treatments. Chenopodium album was the most common annual species in all treatments. We found that herbicide application in the CONFYM treatment decreased the density of the most sensitive species (e.g., C. album, Polygonum convolvulus, Mentha arvensis, Polygonum persicaria, Elytrigia repens) but had a minor or no effect on the proportion of herbicide-tolerant species (especially Viola arvensis, Veronica spp., Myosotis arvensis). Among the perennials E. repens was the most common species in all treatments. The highest number of these plants occurred in the ORGGRM treatment. We found that the species pool was larger and the average number of species higher in the organic than in the conventional treatment. No significant difference was identified between the organic treatments. Our results suggest that weed species diversity could be promoted by using organic cropping practices.