I have two comments about this question:

1) Life can live in all kinds of places. I work in wetlands, where the soils can vary widely in redox potential, organic matter content, soil salinity, pH, nutrient levels, texture, and more from one wetland to the next (and sometimes within a single wetland over time). Therefore, life can live in a soils across a wide variety of physicochemical conditions. Thus, one couldn't make a general statement about the optimum conditions for life unless you want really wide ranges on those numbers (e.g., "Life can can live in soils ranging from almost 100% organic matter to nearly 100% mineral material" is true, but not especially useful). 

2) I think the question about optimal ranges would vary from organism to organism, depending on the environmental conditions that each organism was exposed to over the course of evolutionary time. Are you asking about life in general, or specific groups of organisms (e.g., microbes, invertebrates, plants), or specific species?

There are some soil properties we can manage, others no. Soil chemical properties are more easily manage. some physical properties are difficult. But we have to analyse  in a whole way. One approach  is the pedoenvironment. Soil, relief, climate and so on.

As Scott answered, it depends on what form of life we are thinking about.  To sustain any form life, essential thing is water.  If there is water, soil is fit to sustain some form of life.

If we are thinking about higher form of life for productive purposes (e.g. plant life), then comes all other nutritional and environmental factors and optimum ranges.

Soil has both inherent and dynamic qualities (USDA, 2006). Inherent soil quality is a soil’s natural ability to function. For example, sandy soil drains faster than a clayey one. Deep soil has more room for roots than soils with bedrock near the surface. These characteristics are permanent and do not change easily. The inherent quality of soils is often used to compare the abilities of one soil against another, and to evaluate the value or suitability of soils for specific uses. Traditional studies in land evaluation have been basically concerned with the practical interpretation of inherent soil properties (soil suitability) such as inventoried in soil surveys.

Dynamic soil quality is how soil changes depending on how it is managed. Management choices affect the amount of soil organic matter, soil structure, and water- and nutrient-holding capacity. One goal of soil-quality research is to learn how to manage soil in a way that improves its functions. This dynamic aspect of soil quality is the focal point of assessing and maintaining healthy soil resources.

According to the soil factors considered, the soil quality can be physical, chemical, or biological. Most of the physicochemical factors are related to inherent soil quality, and biological and some physical factors with the dynamic soil quality. Although soil quality often focuses on biological aspects, this must not diminish the importance of physical and chemical factors (Ball & De la Rosa, 2006).

Table .  Soil attributes which may be used as indicators of  soil quality

Grouping type                                          Soil indicators                                                                                                                                                  

Physical attributes                                                                                                                                                      Soil texture

                                                                      Stoniness

                                                                    Soil structure

                                                                      Bulk density

                                                                      Porosity

                                                              Aggregate strength and stability

                                                                      Soil crusting

                                                                      Soil compaction

                                                                       Drainage

                                                                        Water retention

                                                                        Infiltration

                                                                        Hydraulic conductivity

                                                                        Topsoil depth

Chemical attributes                                                                                                                                                       Color

                                                                      Reaction(pH)

                                                                       Carbonate content

                                                                        Salinity

                                                                         Sodium saturation

                                                                         Cation exchange capacity

                                                                         Plant nutrients

                                                                         Toxic elements

Biological attributes                                                                                                                                                    Organic matter content

                                                                    Populations of organisms

                                                                    Fractions of organic matter

                                                                    Microbial biomass

                                                                     Respiration rate

                                                                      Mycorrhizal associations

                                                                      Nematode communities

                                                                      Enzyme activities

                                                                      Fatty acid profiles

                                                           Bioavailability of contaminants

 Key indicators selected by the USDA (2006)

I wish you success!!!

Thanks all for your valuable inputs. I am particularly interested in arthropod fauna(microarthropods). My doubt is, without doing any microscopic examination, is there any way to predict whether there is a possibility of finding soil microarthropod fauna?Can any physicochemical factor apart from organic matter act as a predictor?

Optimum range of this parameters is very different from landscape to landscape and from a living organism to organism. One and the same conditions are very dynamic in time and space, thus You need to know exactly ultimate goal of research and than assess the value of soil parameters

How have already responded earlier, the plant life can thrive even in soft rock that can not be considered ground. Only water and certain minerals which condition the type of vegetation is needed.

A soil, by definition, contains life or is influenced by organisms; otherwise, it is simply parent material. As others have stated, many variables will influence the abundance, diversity and growth of organisms (micro-arthropods in your case). The trick is to find the limiting variable(s). Moisture, O2, pH, and organic mater will all be factors and many are related. Furthermore, as with most ecological systems, relationships between biological processes and environmental variables are not simply linear; logistic or unimodal relationships are common.

In your case, I would assume that the easiest metric to estimate soil diversity and/or arthropod biomass would be a remotely sensed estimate of above-ground productivity (such as Leaf Area Index from MODIS). Productivity, above-ground biomass or LAI could also be measured at the plot level if you have the resources. Leaf area, biomass and productivity are all related, as will be the inputs to the soil and hence the abundance and biomass of detriavores that will feed the predatory arthropods, etc.  

Good luck!

HI,I feel pH  of the soil is an important  parameter to identify the sustainability.Lpw cost instruments are available toanalyse temperature,ph,salinity,conductance etc

In my opinion one should consider all parameters ie physical, chemical and biological soil. The three features are dependent on each other.

I feel , soil texture as apart of soil physical property ,pH as apart of chemical property and soil respiration as a part of biological property will surely give some concrete indications of sustaining  the plant  life . There could be many more added to make it more complex . But these are three soil properties  to my mind.

Kind of a chicken and egg dilemma.  Previous answer present different angles. There should be a bio-physical environment that procure energy so organisms can feed and reproduce. Oxygen is  a requirement for most chemical reaction but some can find another source. Nutriment should be available (some say six essential elemental ingredients: carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur). And there should be some kind of stability for population to survive so adaptation to extreme conditions (relative to the needs of that population) do not require so much energy that it can not feed and reproduce. And it can be seen like a hierarchy of sub-systems of populations integrated as food web in a larger ecosystem.

 Hi, Lakshmi!

From my own experience I can advise the integral indicator of the “soil health” - the level of labile (active) organic matter. Active organic matter is a good indicator of soil biological health. It is highly simplifed method in which neutral dilute solutions of potassium permanganate (KMnO4) reacts with most of the active fractions of SOM, changing the deep purple color of the solution to a light pink color.The lighter the color of the KMnO4 solution after reacting with soil, the greater the amount of active organic matter content, and the better the quality of the soil.

Best regards

Interesting discussion on physico-chemical properties of soil for sustenance of life.In soil we have chemical environment and physical and biological conditions for the life to sustain.Soil pH,redox conditions and electrical conductivity determine the ionic environment but plant nutrients in available form are also needed to support life.Soil texture and structure will decide the air and water relations for life.Among the biological conditions there should be microbial (population)life and to support it soil organic matter is required. The microbial processes will in turn support any other form of life,plant animal etc.