Populations of nematode genera in soils under pasture

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Abstract
Dryland and irrigated pastures, with dry matter yields of 3000 and 14 000 kg/ha/year, on Otiake silt loam were sampled monthly from September 1974 to October 1975. Under dryland pasture the mean nematode population was 730 000/m2 in 0–10 cm soil depth, and monthly populations fluctuated significantly with changes in soil temperature and moisture. With irrigation the nematodes increased to 1 970 000/m2; in the absence of natural periods of moisture stress the correlations with soil temperature and moisture were not significant, irrigation increased populations of Pratylenchus, Paratylenchus, and Rhabditidae, and decreased Tylenchus and Cephalenchus. At the dryland site the peak populations coincided with the onset of drought, so plants would suffer the combination of moisture and nematode stress. Under irrigation, however, this relationship did not hold, and although Pratylenchus and Paratylenchus both increased (22.8 × and 3.7 × respectively) their absolute effect on plant production probably changed little.