VARIATION OF 4 PHOSPHORUS PROPERTIES IN WOODLAND SOILS

Variation in total, organic and available-P contents and phosphatase activity of P-deficient soils of some English Lake District woodlands of differing vegetative composition were examined in relation to individual woodlands, two depths in the soil profile, mull, moder and mor humus types, and different times of the year. Depth in the soil profile was a more important source of variation in the P properties than different woodlands. Soils in individual woodlands differed in their degree of variability in the four P properties. Available P contents and phosphatase activities were more variable than total and organic P contents. Available-P and organic-P contents and phosphatase activity showed seasonal variation. Seasonal variation in available-P was almost as great as differences in available-P between woodlands. Total and organic-P contents showed similar patterns of variation with respect to individual woodlands, humus type and soil depth. Differences in degree of variation within woodlands and differences in degree and pattern of variation of the four P-properties may need to be taken into account in soil sampling programmes of studies comparing soils under differing vegetation regimes. Different interpretations of the variation in the soil-P properties were obtained by expressing the data respectively in terms of soil weight (g-1 soil) or soil volume (cm-1 soil), due to marked variation in bulk-densities of the woodland soils. It is suggested that where soils vary in bulk-density, soil data should be expressed in terms of soil volume. The P-deficiency of the woodland soils is probably associated with the relatively low total P content per unit volume of soil and the high proportion of it which is organically bound. © 1979.