This is a burning question for most people starting out on a soil health program. The answer is "it depends"...a trademark response of one of my colleagues. This response is a frustrating tease on the face of it, but it is absolutely correct.
There are many factors contributing to soil health and balancing all of these is not a job for clowns. Remember we need Chemical, Biological and Structural aspects of the soil to work together for soil health, so we need to look at a number of indicators that will guide us toward an assessment of how far we are behind on each factor. A reliable chemical soil test, a profile assessment and an accredited biological assay will give us a lot of the information we need to plan a program of soil health improvement (amelioration).
A ph, EC, field texture test, the assessment of moisture, colour and smell are the easiest ways to start this investigation.
pH tells us our acidity,(percentage Hydrogen) this is a quick way of assessing availability of elements to plants and the environment for microbes in the soil.
EC or electrical Conductivity tells us the load of conductive elements (salts) we have and this may indicate recent fertiliser application or salinity or a lack of both.
A field texture test will roughly determine the particle size, surface area as well as water and nutrient holding potential of a soil. Texture is also critical information for planning irrigation amounts and frequency as well as fertiliser application timing and output.
Colour will give us a clue to geology of the parent material, presence of organic matter, water logging of the soil and general characteristics of nutrient availability.
Smell will tell us if a soil is sick (rotten egg gas) or vibrant and healthy (complex earthy smell with a hint of mushrooms.)
A wet soil should be left to drain, a moist friable soil is our target and a dry soil is a tragedy for all but Cactii lovers and lab technicians.
Temperature and moisture are major catalysts for soil microbes and chemistry. the ideal growing temperature for most plants is in the low 20 degrees Celcius range, this suits rampant activity from worms and most soil grazers as well as the microbes and the shredding, digesting, cellular division, breeding and predation that drives the soil food web is at its peak here. Soil moisture sitting between 30-50% depending on the plant species selected also helps with soil air availability and this is critical for aerobic biology, these are soil health bringing microbes. Pathogens, the disease creators are usually favoured by low soil air conditions as this destroys or excludes aerobic biology.
With everything working for us we can begin to improve all aspects of soil health immediately. Some of my clients report instant responses to compost or compost tea applications, the majority see a gradual improvement, imperceptible at times except for the absence of disease and an improvement in crop yield and quality that sneaks up on them.
The certainty here is that with time, temperature, moisture, well planned and carefully guided activity, you will notice a change in your plants, your pastures and your food when soil health is addressed.