Populations of nematode genera in soils under pasture

Abstract

Pastures on Tokomaru silt loam under two types of management were sampled monthly between September 1974 and October 1975 for nematode populations: (i) dryland pasture with a dry matter yield of 12 000 kg/ha/year (ii) pasture with a dry matter yield of 15-18 000 kg/ha/year, spray-irrigated with dairy shed effluent. Samples collected in February and July showed that of the nematodes in the upper 30 cm of soil at least 84% occurred in the upper 10 cm. Analysis of monthly samples indicated that although populations were greater in 0–5 cm than in 5–10 cm zones, seasonal trends of genera were similar at both depths, and therefore the sites have been compared on a 0–10 cm basis. Under dryland pasture the mean nematode population in 0–10 cm soil depth was 1214 000/m² and 1 477 000/m² with effluent irrigation; in both pastures monthly populations fluctuated significantly with changes in soil temperature and moisture. Effluent irrigation led to changes of at least 5% in populations of Tylenchus, Helicotylenchus, Pungentus, and Aporcelaimus. Pratylenchus was not found at the dryland site, but reached 33 800/m² at the effluent-irrigated site. Bacterial feeders increased from 29.7 to 37.0% and this was offset by a decrease in Dorylaimida. In general, changes in the nematode fauna were small and unlikely to influence pasture performance.