Soil quality is regarded here as the measure of inherent physical properties, it’s use is therefore a theoretical measure of what the soil is capable of in the absence of any other limitation. As a measure or value in itself it reveals value about the soils likely potential but not the extent to which that potential is realised. Thus quality is a theoretical value which represents the maximum potential of the soil.
In this respect it is the very absence of consideration for other limitations, many of which could be considered variables and so aspects of Soil Fertility rather than Quality, that permits the potential to create a simple Universal Soil Quality Index (USQI).
Soil Quality = f (Land / inherent properties)
The concept of a USQI
Using a USQI any soil, regardless of location or external factors, could be given a theoretical value against which a potential may be calculated. This could then be adjusted to take into consideration the absolute limitations imposed by major variables (i.e. climatic/hydrological, nutrient/micro-biological limitations). Thus the USQI can be used to develop an ideal value (one in the absence of any other consideration) and from that an optimum value (one that considers general limitations imposed by ‘chaotic’ variables) that acts as both a regional soil quality index and a potential optimum value that can be realistically achieved (PrSQI). This Potential optimum could be expressed as a function of the inherent properties as they are bound by common climatic variables.
Soil Potential = f (Land / inherent properties)/ climatic variables
“soil fertility is now the measure of the degree to which the Soil potential is actually realised” this the soil function.
next chapter: Soil Properties
Free Cultural Works (CC-BY=NC-SA) Malcolm McEwen 2011