Soil nematodes in new zealand pastures
1977
Yeates, G. W.
In the last five years attention has been drawn to the importance of plant and soil nematodes in limiting pasture production. Distribution of nematode genera has been studied and work on their abundance and dynamics is in progress. Monthly sampling carried out over 13 months has shown a strong correlation between soil moisture falling below wilting point and decline in total nematode abundance; annual mean populations range from 730,000 to 4,890,000/m for 0–10 cm soil depth. At six sites the vertical distribution of nematodes in 0–30 cm soil was strongly correlated with both soil organic C and Truog P; at four sites 75 percent of the nematodes were recovered from the upper 5 cm. Management of permanent pasture may lead to increases in populations of nematodes including Heterodera and Pratylenchus; buildup of Praty-lenchus was correlated with lack of pasture response despite a fourfold increase in phosphate application. Cultivating and cropping an old pasture has been found to reduce demaging nematode populations. Considerable work has been carried out with the clover root nematodes Heterodera trifolii and Meloidogyne hapla. In the field, herbage dry matter responses to their chemical control, or control of H. trifolli where it occurs alone, have been about 10 percent. Pot trials have shown that H. trifolii and M. hapla not only reduce the rate of herbage production but also its nitrogen content.
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