Populations of nematode genera in soils under pasture

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Abstract
Mean totals for nematode populations found in 12 samples of 0-10 cm soil from grazed pastures, taken monthly, are 1,500,000/m2 for Rotoiti loamy sand, 1,030,000/m2 for Kokatau silt loam, 4,750,000/m2 for Kaitoke silt loam, 960,000/m2 for Judgeford silt loam and 790,000/m2 for Pomare silt loam. These totals are positively correlated with annual herbage production at the sites. Population levels of the 40 taxa distinguished (most of them genera) were poorly correlated with seasonal variation in the environmental factors measured; the factors operating are unknown because of inadequate knowledge of nematode biology. Genera contributing at least 4% to total numbers at 2 or more sites are Cephalenchus, Helicotylenchus, Pratylenchus, Paratylenchus, Cephalobus, Heterocephalobus, Anaplectus, Chronogaster, Pungentus and Aporcelaimus. Mean and maximum population levels are given for each genus and site; this information is useful in estimating any damage these nematodes may cause and in determining their role in cycling nutrients in the soil.