IFEVA   02662
INSTITUTO DE INVESTIGACIONES FISIOLOGICAS Y ECOLOGICAS VINCULADAS A LA AGRICULTURA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Long-term changes in the weed communities of intensively managed cropland: Effects on species diversity and functional composition
Autor/es:
POGGIO, SANTIAGO L.; GHERSA, CLAUDIO M.
Reunión:
Congreso; 16th European Weed Research Society Symposium; 2013
Institución organizadora:
European Weed Research Society
Resumen:
Weed communities shift in response to changes in cropping systems, such as the adoption of no-tillage. In addition, different weed assemblages may occur in different crop types. Interestingly, weed shifts are rarely studied in the long-term. Here, we study the changes in the arable flora of the Rolling Pampa, the corn-belt of Argentina, since the early 20th century. We focus on maize and soybean, the most important warm-season crops in region. Maize expanded at the 1900s. Soybean was introduced during the 1970s, and considerably expanded since the inception of glyphosate tolerant GM-soybean sowing in 1996. Weeds were surveyed during the summer seasons between 2004 and 2011. Previous research on weeds of warm-season crops was also included. Historical data on crop management was compiled. Regional species richness (gamma diversity) was accumulated for particular periods associated with key technological changes. gamma diversity was additively partitioned into local (alpha diversity) and turnover (beta diversity) components (beta diversity = gamma diversity − alpha diversity). Species were classified according to origin and functional traits. Weed flora of maize crops was enriched in c. 7 species per decade between 1920s and 1995. Subsequently, weed flora of warm-season crops lose nearly 3 species per year (gamma = 99 to 49). Beta diversity decline (85 to 41) mainly reflected regional richness loss. Mean a-diversity similarly decreased in soybean (13.8 to 6.9) and maize (14.0 to 7.3) since 1995. Land-use changes explain beta diversity decrease. No-tillage, adopted in the late 1980s, almost completely replaced ploughing and is the usual practice nowadays. Maize sown area considerably decreased due to the widespread sown of soybean. Weed control now remains on a narrow spectrum of active ingredients. Glyphosate, which was mostly applied during fallows and pre-sowing before GM-soybean adoption, has now become the most common post-emergent herbicide. Pasture ploughing and fencerow removal to increase cropland changed the proportions of source and sink habitats consequently altering dispersal relationships between cropped and non-cropped habitats. Frequency of common weed species from Asteraceae and Poaceae decayed during the 2000s, whereas few species occurred as new weeds of warm-season crops in the region (Parietaria debilis, Urochloa platyphylla). No-tillage hindered weed species requiring regular ploughing to perpetuate within fields (Datura ferox, Sorghum halepense), whereas promoted small-seed weeds (Digitaria sanguinalis, Euphorbia maculata), wind-dispersed species (Conyza bonariensis), and woody species (Sida rhombifolia, Gleditsia triacanthos). Crop productivity increase since the 1990s would have restricted the occurrence of most C4 species. Our results highlight that long-term changes in weed communities, in terms of species diversity and functional composition, are driven by both transformation in cropping systems due to the adoption of new technologies at wider spatial scales, and by both management and ecophysiological attributes of particular crop types at field scale.