Description of the agricultural management and crop yield, averaged over the five years before the first sampling date, in June 2009 (2005–2009).

aNumber of soybean cycles to number of maize cycles over the last 5years. bPercentage of winters that wheat was planted as a winter crop. cPercentage of winters that a cover crop (Vicia sp., Melilotus alba or Lolium perenne) was planted. Cover crops were chemically burned before summer crops are planted. dCalculated as liters of low-toxicity herbicides plus liters of moderate-toxicity herbicides weighted by two. Toxicity was defined according to EPA Toxicity Categories. Unit: total liters over 5 years. eNo maize was planted in the last 5 years.