Environmental and management effects on the composition of weed communities from the rolling and Inland Pampa, Argentina.

DIEGO OMAR FERRARO; SUAREZ, S.A.; DE LA FUENTE, ELBA B.; POGGIO, S.L.; GARCIA, W.; LEON, R.J.C.; GHERSA, C. M.

Durban, South Africa

Congreso; IV International Weed Science Congress; 2004

Soil and climate are the main regional factors determining the structure of plant communities. But in agroecosystems, these factors interact with the environmental modifications derived from management practices (e.g. tillage and pesticides) resulting in novel ecological conditions that mold crop-weed plant assemblages. In order to evaluate the environmental and management effects on weed community, its floristic composition was studied collecting data of species presence and management histories of cropped fields from two subunits of the Pampas (Inland and Rolling Pampa). We calculated two indexes that reflect the level of pesticide and tillage use in each field. Results from multivariate analyses (principal components and cluster analysis) indicate that weed communities of each region were different. Analysis of similarity (ANOSIM) of these data showed a significant regional effect on weed assemblages, but no significant dissimilarity between farms and crops within each region (P < 0.001). Among the management aspects evaluated, only the pesticide toxicity to insects and the years of continuous cropping were significantly associated with weed composition, with no evident tillage effect. When effects on weed species richness were evaluated, the effect of pesticides and the years of continuous cropping were also evident, with increasing richness as environmental impact decrease. However, there was no correlation between species richness and tillage impact. Our results may indicate both a strong regional effect on controlling final composition community and pesticide use and continuous cropping as two important on-farm factors affecting weed composition.