Soybean weed community composition and richness between 1995 and 2003 in the Rolling Pampas (Argentina)

The introduction of new agricultural practices (no tillage cropping and soybean transgenic cultivars resistant to glyphosate) to Argentina, together with market factors, have resulted in an increase in the area cropped with soybean and generated a new environment in the Rolling Pampas agroecosystem. During the summers of 1995, 1998, 1999, 2001 and 2003, a total of 120 soybean fields were surveyed, to evaluate the changes in the weed communities of the central Rolling Pampas through the period during which the adoption of these new technologies was increasing exponentially. Floristic structure was analyzed in terms of species composition, and functional structure in terms of morphotypes and physiotypes. Data were summarized by calculating species constancy, and alpha, beta, gamma diversity and functional richness. Alpha (local) diversity and functional richness were linearly related with gamma (regional) diversity and after an initial increase from 1995 to 1998, decreased over time, this being associated with the adoption of the new technologies. Beta diversity was not related to soybean regional pool of weed species, thus it was probably related to the availability of refuges provided by the landscape's habitat. Tillage system and cultivars were the main agronomic variable affecting the occurrence of weeds.