VARIABILITY IN 3 AREAS OF DENCHWORTH SOIL MAP UNIT .1. PURITY OF MAP UNIT AND PROPERTY VARIABILITY WITHIN IT

Variability of soil within 3 areas of the Denchworth map unit in S England was investigated by describing and analyzing samples from 30 profiles located at the intersects of a randomly oriented grid. The Denchworth series was mapped over several stratigraphically different clays, and the areas chosen provide 3 groups of profiles developed over Gault (Cretaceous), Kimmeridge and Oxford (Jurassic) clay, respectively. Purity of the map unit, estimated as the percentage of profiles whose data agree with the definition of the Denchworth series, was 60%, which is comparable with values for other map units both near by and elsewhere. The variability of individual properties as indicated by coefficients of variation differed widely. Generally, physical properties were more uniform than chemical properties. The Denchworth map unit can consequently be treated uniformly for aspects of land management related to soil physical properties, but it provides little guidance for fertilizer application. A small amount of variability can be attributed to mapping together those soils developed in material derived from stratigraphically different clays, but is insufficient to justify separating them.