A SOIL-LANDSCAPE MODEL FOR CLOSE-JOINTED MUDSTONE, GISBORNE-EAST CAPE, NORTH-ISLAND, NEW-ZEALAND

A soil-landscape model, comprising 12 land components at a scale of 1 : 5000, has been developed in Neogene close-jointed mudstone in the Gi sborne-East Cape region of the North Island, New Zealand. In a validat ion, soil order was predicted correctly in 81% of observations, soil g roup in 80%, soil subgroup in 63% and soilform in 60% of observations. A simplified model based on 11 land components for use at a scale of 1 : 50 000 has also been validated. Here soil order was predicted corr ectly in 71% of observations, soil group in 73% and soil subgroup in 4 9% of observations. For application with a digital elevation model (1 : 50 000), the number of land components was amalgamated to five. Here the soil order and soil group were predicted correctly in 63% of obse rvations and soil subgroup in 40% of observations during validation. I n all trials, the percentage of correct observations increased if a se cond choice or subdominant soil class was allowed. It took 2 person-we eks to produce a soil map from the 1 :50 000 form of the model over 40 0 km2 of steep and hilly country by photo interpretation of stereo aer ial photographs, compared with 1 day of applying computer algorithms o n the digital elevation model (DEM). The soil-landscape model succinct ly relates soil class to land component and it enables improved target ing of farm and planning inputs by empowering existing research into s oil fertilizer requirements and soil physical properties.