Weed Community as an Indicator of Summer Crop Yield and Site Quality

Abstract

We studied relationships between weed community characteristics and management practices, soil degradation (reductions of the A horizon, organic matter, total N, and available P) levels, and soybean [Glycine max (L.) Merr.] and corn (Zea mays L.). Our objective was to provide a scale based on floristic information that could be used to evaluate sites in terms of summer crop yields and agroecosystem degradation. Weed surveys were carried out in 1995 and 1999 in corn and soybean fields. Cluster analysis and canonical correspondence analysis (CCA) were used with data from 1995. Regional or gamma diversity, local or alpha diversity, and exchange of species between habitats or beta diversity of weed communities were estimated as well as changes in origin, morphotype, and life cycle for data from both surveys. Four weed communities related to crops and yields were identified. In both corn and soybean fields, the potential for high crop yield (low soil degradation) may be indicated by the presence of the weed groups identifying the weed community of a crop species. Sowing date, agronomic index, mechanical control, and the use of grass herbicide also accounted for weed community structure. Sites with higher than average yield had the highest alpha diversity. The number of native species in the community was related to soil degradation levels. Soil degradation proved to be more important than type of crop in determining the structure of a weed community.