Micromorphological observations on the effects of land use differences on some New Zealand soils

Open Access
Publisher Website
Google Scholar
Abstract
Differences in the humus forms and the microfabrics of 29 topsoils from seven soils, including moderately and strongly leached yellow-grey and yellow-brown earths, a yellow-brown pumice soil, and a yellow-brown loam, are described. The differences are considered under native forest, tussock grassland, fernland and scrub, exotic forest, and under untopdressed and topdressed pastures. The humus forms under native dicotylous or podocarp-dicotylous forest and scrub, vary from thick, laminated mors over mulls to mor-like mulls and strongly granular mulls. All contain abundant plant residues at or near the surface. In most examples the Ai horizons are porous with strongly developed granular structures and mull humus microfabrics. Under tussock grassland laminated mulls are characteristic but soils have Ai horizons with finely granular structure and mull-like moder microfabrics. Under bracken fernland laminated mors contain moder microfabrics, underlain in at least one soil by a bleached A horizon. Beneath exotic radiata pine are laminated mors and laminated mulls, but underlying the moroid humus layers are granular mulloid A, horizons that contain mull humus microfabrics. When forest soils are converted to introduced pasture three general trends are recognised: a decrease in the concentration of organic matter near the soil surface, a decrease in the amount and development of granular structure, and a decrease in interpedal porosity. These trends are towards weakly granular mull with a weak mull humus microfabric. The trends are reversed beneath topdressed pasture except that, in addition, the Ai horizon is generally thickened so that development is towards strongly granular mull with a strong mull humus microfabric. Under heavy stocking when wet, soils of topdressed pasture develop a platy structure at the surface, but recovery of the structure appears to be quite rapid under vigorously growing pasture in a soil with high nutrient status.

This publication has 5 references indexed in Scilit: