My thesis investigates soil recovery following landsliding in steepland and hill country on part of the Whatawhata Research Station, 25 km west of Hamilton, North Island, New Zealand. Underlain mainly by Mesozoic greywacke, six landslides were studied, ranging in activation time from pre-1953 to 2014. On the basis of geomorphological analysis the landslides were divided into five zones: shear zones (mean of 25 % of landslide area), intact accumulation zones (20 %), transition zones (40 %), and re-deposition zones (15 %), plus an adjacent control zone. Soil physical and chemical properties including: solum depth, A horizon depth, particle size, and soil dry bulk density, along with, soil C, N, P, and pH were determined for each zone of each landslide.
Soils were well-developed in the control and intact accumulation zones and least recovered in the shear and re-deposition zones. Mean A horizon depths ranged from 2 cm in the shear and re-deposition zones to 7 cm in the transition zones, 17 cm in the intact accumulation zones, and 20 cm in the control. Mean solum depths ranged from 24 cm in the shear zones, 91 cm in the intact accumulation zones, 72 cm in the transition zones, 90 cm in the re-deposition zones and >100 cm in the control zones.
The differences between zones within the landslides were greater than the differences between landslides. The controls had higher (P<0.05) C contents than any of the zones within the landslides, and the intact accumulation zones had higher (P<0.05) C contents than the shear, transition or re-deposition zones. Mean soil C contents ranged from 8.2 % in the controls through 5.4 % (intact accumulation zones), 4.2 % (transition zones), 3.2 % (re-deposition zones) to 2.6 % in the shear zones.
Similarly to C, the total N was higher in the controls than the other zones (P<0.05). Mean N content ranged from 0.2 % in the shear zones, 0.3 % in the transition and re-deposition zones, 0.5 % in the intact accumulation zones to 0.7 % in the control zones.
The C:N ratio was consistent across all zones in all six landslides and controls, ranging from 11 to 16. There were no significant differences in the C:N ratio between zones of the landslides or with landslide age.
Soil Olsen P was lower (P<0.05) in the shear and re-deposition zones than the control, intact accumulation, and transition zones. There were no significant differences in Olsen P between the intact accumulation, transition, and control zones. Soil pH was generally low (4.8 to 5.6) across all zones in all six landslides and soil dry bulk density was variable. Thus soil pH, dry bulk density, and Olsen P were not correlated with soil recovery and development.
Overall the shear zone occupied <25 % of the landslide area, was the slowest zone to recover, and was the least productive. The intact accumulation, transition, and re-deposition zones generally consisted of about 75 % of the landslide area, and once stabilised were expected to be relatively productive.
