Distribution and population dynamics of nematodes in a rice field and pasture in India.

Ecological studies on soil nematodes were made in a tropical rice field and pasture. Parasitic species were more diversified in the pasture than in the rice field. Eighty-six and sixty percent of total nematodes occurred in the top 10 cm in rice field and pasture, respectively. Nematodes were not randomly or uniformly dispersed but aggregated. Parasitic forms were most abundant and correlated with root biomass in the 0-15-cm soil layer, the greatest number usually occurring at the 10-15-cm depth at both sites. In summer, however, they were densest at the 15-30-cm depth. Microbivores were most frequent in the top 5 cm of both sites. Micellaneous feeders (food sources uncertain) usually occurred in highest densities at the 15-30-cm depth. Predators showed no distinct depth preference. Temperature and moisture of the soil apparently played an important role in regulating nematode population. Peak densities of 31.3 x 10/m(2) and 21.6 x 10/m(2) at a 30-cm depth occurred in January, while minimum densities of 5.0-5.3 x 10/m(2) and 4.1 x 10/m(2) occurred in July-October and April in rice field and pasture, respectively. Monthly mean biomass of nematodes was 23.8 +/- 4.5 mg/m(2) in rice field and 11.5 +/- 1.5 mg/m(2) in pasture.