Item

Soil-landscape modelling and soil fertility in Pokororo Catchment, Motueka, New Zealand

Betitis, Thomas L.
Date
1999
Type
Thesis
Fields of Research
Abstract
Plantation forestry is a major land use in steepland and hill country regions of New Zealand. Soil information is an important resource which allows managers to enhance productivity and minimise cost while maintaining sustainability of the site. However, soils of these areas have often only been mapped at a reconnaissance level, and further, more detailed soil survey carried out on traditional lines is very unlikely. Soil-landscape modelling, within the land systems approach utilises hierarchical landscape analysis as a basis for examining and predicting soil pattern over a range of scales. It is an efficient alternative to conventional soil survey for hill and steeplands. This approach was applied in a study of Pokororo catchment, near Motueka, northwest Nelson, New Zealand to improve soil resource information and provide soil data relevant to plantation forestry. Three land systems (Brooklyn [BLS], Brooklyn-Pikikiruna [B-PLS] and Kaiteriteri [KLS]) were delineated based on the underlying geology. A second order drainage basin was selected in each land system as a study window. Soil observations were conducted across land components of the second order drainage basins. Soil samples for analyses of pH, organic C, total N, Bray 2 P and Bray cations (K, Mg, Ca) were taken at three depths (0-10 cm, 10-20 cm, and 20-40 cm). The results showed that the soil pattern varied consistently between and within the three land systems and was related to the underlying parent material, its weathering state and topographic position. A continuous debris mantle regolith exists across land components within all three land systems and soil development is spatially controlled. The concepts of excavation, recovery and residence were used to explain soil development and variability. Brown Soils are dominant and are differentiated at subgroup level. Bray 2 P data showed marked variability between but not within land systems. The BLS and B-PLS covering mafic and mafic felsic geology respectively had extremely high levels (>> 12 µg g⁻¹) while the KLS, on highly weathered granite was generally very low (>>12 µg g⁻¹). Soil pH in the KLS was generally lower (<5.0) than in the other two land systems. Boron deficiency is widespread across all land systems while organic C, total N and Bray cations were generally adequate. Based on these results, it is recommended forest management be based on the land systems delineated. Low Bray 2 P data in the KLS indicate that fertiliser programmes should specifically target this land system especially for fertiliser P.
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