Soil Science

Field pH and Colour

Field pH Test

Soil pH is a measure of the concentration of hydrogen ions in the soil solution. Soil pH, as an indicator of acidity or alkalinity, provides important practical information about fertility and other soil properties needed to understand ecosystems, as well as land use suitability and hazards. Soil pH can range from as acid as 2 to as alkaline as 10, with most soils between pH 4 and 8.

Soil field pH is determined by mixing a soil sample with a universal indicator solution, and then sprinkling the surface with barium sulfate powder.  The indicator is absorbed by the white powder, and the colour is observed and compared a standard set of colours.  The field pH corresponds to laboratory pH measured in water, and is accurate to about 0.5 pH units

Field Colour Test

Colour is described using the Munsell colour system, in which a piece of the soil is visually matched to a "chip" in the Munsell Soil Colour Chart.  When dry soil is moistened the colour darkens, so it is important to specify whether the soil is dry or moist.  Unless there is a particular reason to do otherwise, always record moist colours.  The system classifies colours using three parameters: Hue, Value and Chroma. Record the dominate colour using the Munsell system.

Hue represents the dominant spectral colour (red, yellow, or a combination of these).  Each page of the book corresponds to one hue, and is given a code such as 10YR.

Value represents the lightness of the colour, expressed as 8/ (light) to 2/ (dark).

Chroma describes the brightness or vividness of the colour increasing from 0 (dull) to 8 (vivid).

The full Munsell colour description is given as code in the following format:

 

 

 

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