The urease activity in profiles of five great soil groups from northern New South Wales

Abstract

The urease activity of soil profiles under swards of improved pasture, from five great soil groups from northern New South Wales, was determined by the modified Hoffmann-Teicher method. Arbitrary sampling depths generally coincided with well differentiated horizon boundaries and comparisons on a depth basis were made among the different soil groups. In all profiles urease activity was higher in the surface soil than in deeper horizons; except in the krasnozem the fall below the surface three inches was sharp. The urease activity below 18 inches in the chocolate soil was higher than in the podzolic and red-brown earth groups. In six samples from podzolic soils containing weathering parent material or gley mottles, no urease activity was detected. The surface 0–3 inches of krasnozem soil, in four out of five profiles, had a lower urease activity than that soil immediately below. The cause of this different pattern of distribution was not determined. A highly significant correlation (r=+0.875) between urease activity and soil organic carbon indicated a moderately strong positive relationship. In the krasnozem this relationship was highly significant (r = +0.929) and in the red-brown earth and yellow podzolic soils significant correlations (r=+0.918, r=+0.777) were found. The correlation of urease activity and soil reaction for all soils was not significant. The presence of gleyed zones in the gley podzolic soil and the higher pH of the red-brown earth are discussed as other factors influencing the pattern of urease activity distribution in the soil profiles examined.