A list of arable farmers in Canterbury was obtained from the
Foundation for Arable Research, Lincoln (http://www.far.org.nz)
and OPENZ (Organic Products Exporters of New Zealand; http://
www.organicsnewzealand.org.nz) provided the contacts for all
organic farmers. The latter were contacted first by a letter,
followed by a telephone call and a meeting to collect detailed
information about the farming practices and the crops grown, as
well as soil type, crop rotation practices, etc. (Table 1). Arable
organic farms were selected from the above list, one to three fields
being selected per farm based on there being an arable crop grown
at the time of the survey. After this, conventional arable farms that
were within 5 km of the organic fields were contacted. The latter
were selected because they were growing similar crops and had
similar soil types. The crops were wheat, barley, carrots for seed,
process peas, field beans, white clover for seed and onions
(Table 1). The number of conventional and organic fields in each of
those crops was the same. The 29th field (conventional) was in
peas. Codes O1–O14 were assigned to the organic fields and C1–
C15 to the conventional ones.