THE EFFECT OF SOIL-PH ON YIELD LOSSES CAUSED BY THE POTATO CYST-NEMATODE GLOBODERA-PALLIDA

The effect of soil pH on yield losses due to potato cyst nematodes (Gl obodera pallida) was investigated in experiments in the field and in a semi-controlled environment. Through annually liming a reclaimed peat soil with about 22% organic matter, plots with pH levels of 4.5, 5.0, 5.5, 6.0 and 6.5 were obtained. In 1990 potato yields in these plots decreased from 45 t/ha at pH 4.5 to 33 t/ha at pH 6.5, whereas the nem atode densities decreased from about 18 to 9 juveniles per g soil. In a container experiment a strong interaction was recorded between soil pH and the presence of nematodes. Tuber yields were about 11% lower at pH 6.5 than at pH 4.5 in the absence of nematodes, but about 44% lowe r when an initial population of 27 juveniles per g soil was present.