Heterodera schachtii (Schmidt) and Soil Acidity

Abstract

1. The possibility of correlating the acidity of the soil with the distribution of cysts of Heterodera schachtii is investigated by a colorimetric method of hydrogen ion determination. The variety of this eelworm which infests potatoes is alone considered, the material being derived from South Lincolnshire—in particular from Kirton and the district around Boston. The samples, general notes and cyst-concentration data are due to Morgan, to whom the writer is greatly indebted.2. A brief account of the life-history of H. schachtii is given, and also:3. A note on the theoretical aspect of hydrogen ions and of the colorimetric methods for determining their concentrations.4. The technique involved is fully discussed, and after various tests is standardized as follows : 2 grams of dry, finely-sieved soil are shaken up with 10 c.c. of twice-distilled water for ¼ hour. The mixture is centrifuged for 5 minutes and diluted with water in the ratio 1:9. A suitable indicator is added, aeration of the solution follows, and the pH-value is read by comparison with indicator-standards in a Walpole Comparator.It is pointed out that at most the results give the pH-value of the solutions. The pH-value of the soil itself, in situ, is not determined, so that the results are only of relational value.