The available-water capacities of North Auckland soils

Abstract

Abstract Available-water capacities of the principal groups of soils of high clay content in North Auckland have been determined. Within each main soil group they are markedly uniform. Among the soils on sedimentary parent rocks podzolisation is accompanied by larger available-water capacities in the A horizons and smaller ones in some B horizons than are found for unpodzolised soils. Of the soils on volcanic parent rocks, the brown loams on basalt have small available-water capacities, and the brown granular soils, on andesitic rocks, large ones. The large available-water capacities of the A horizons of podzols are related to silty textures, but other differences in available-water capacity among soil groups are best explained by other physical properties. These include high dry bulk densities in the B horizons of some podzolised soils, low dry bulk densities in the B horizons of brown granular soils, and considerable volumes of large, easily drained pores in many brown loams.