Soil samples
Soil samples were collected from four paddy fields used in organic rice production. There were no
indications of industrial pollution, from visual assessment and historical study. Two sites, with cow manure
applied, were located approximately 100 km north, and two sites, with pig manure applied, were located
approximately 120 km west of Bangkok, Thailand (Figure 1). At each site, ten randomly distributed samples
were taken from the 0–15 cm depth (Tandon 1995; Soil and Plant Analysis Council Inc,2000). The soil
samples were air dried, ground to pass a 2 mm sieve and kept in plastic bags prior to analysis.