Variability within a soil mapping unit mapped at the soil type level in the Wanganui district

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Abstract
The variability in 16 morphological properties is described from 31 profiles covering the complete geographical extent of a soil mapping unit (Westmere silt loam) mapped at the soil type level (scale 1 : 31 630) . The properties described include horizon designations and thicknesses; colour hue, value, and chroma; moist consistence; wet consistence (stickiness and plasticity); abundance and distinction of, mottling; development of clay coatings; and the grade, size, and type of structure development. Maximum variability is observed in structure grade and size, and wet consistence, with minimum variability in soil colour (particularly hue) and horizon designations. The maximum number of samples required to obtain a sample mean for any particular morphological property within ± 15% of the total population mean is approximately 20 at an 85% confidence level and approximately 35 at a 95% confidence level. Data showing the variability within soil mapping units should be included in all soil surveys in order to give users a better understanding of the limits of any particular soil mapping unit.