Which environmental and management factors are the most important determinants of arable weed species composition in intensively farmed areas across an area of 93 000 km2? Does the relative importance of environmental and management factors depend on plot location within fields (centre or edge)?
The abundance of late-summer weed flora and 25 environmental, management and site context factors were measured in 243 maize, sunflower and stubble fields representing the entire country. Data were analysed by redundancy analysis (RDA) after backward variable selection. The gross and net effect on weed species composition were calculated for each variable. Variation partitioning based on RDA was used to assess the relative effects of the three groups of explanatory variables.
The net effects of 24 variables on species composition were significant, explaining 25% of the total variation in species data. Most variation in species composition was explained by plot location, which was followed by temperature, crop type, precipitation, soil texture, neighbouring habitat, altitude, soil pH, sodium and potassium content of the soil. Variation partitioning revealed that environmental variables accounted for twice more variance than management variables, but the relative impact of management variables was larger in field cores than in field edges.
Our results suggest that even for intensified agriculture the effects of environmental factors are of greater importance than management factors on summer arable weed composition in a country-wide context. The effects of intensive crop management decrease towards the field periphery.