Comparison of aquatic organisms communities between paddy fields under rice-duck (Aigamo) farming and paddy fields under conventional farming

Farming using "aigamo" (rice-duck; crossbred of wild and domestic duck) is one of the popular organic farming methods for paddy rice in Japan. The diversity and community structure of aquatic organisms under rice-duck farming were investigated and compared with those under conventional farming. Adjacent paddy fields with these different farming methods were selected at two sites. The taxonomical groups and the number of aquatic organisms ranging in size from 30 mum to 2 cm in the floodwater of three collection areas in the respective fields were surveyed every 10 d during the growth period of rice plants. The number of taxonomical groups of aquatic organisms and the frequency of the presence of Stichotrichia were significantly higher in the paddy fields under conventional farming, while the population density of Volvocida was significantly higher in the paddy fields under rice-duck farming (p < 0.05). The number of taxonomical groups during the late flooding period (over 50 d after the onset of flooding) increased more significantly in the fields under conventional farming than in those under rice-duck farming. Principal component analysis showed that Lemnaceae and Chlorococcales mainly composed the communities of aquatic organisms in the fields under conventional farming, while such communities were not observed in the fields under rice-duck farming. The authors could not find any specific community structure of aquatic organisms in the latter farming system.