1. C. J. M. Almekinders, L. O. Fresco, and P. C. Struik .1995 .The need to study and manage variation in agro-ecosystems., Neth. J. Agric. Sci, 43 :127 –142 .
2. Soil properties affecting the distribution of 37 weed species in Danish fields
3. R. E. Blackshaw, J. R. Moyer, and G. C. Kozub .1994 .Efficacy of downy brome herbicides as influenced by soil properties., Can. J. Plant Sci, 74 :177 –183 .
4. M. R. Blumhorst, J. B. Weber, and L. R. Swain .1990 .Efficacy of selected herbicides as influenced by soil properties., Weed Technol, 4 :279 –283 .
5. The analysis of vegetation-environment relationships by canonical correspondence analysis