The most common measure of soil quality is the pH and this is a good general indicator but does not tell you what to do if the pH is too low or too high. Soil pH can also vary during the crop cycle by as much as a whole point. To find out what to do to correct the health and balance of your soil you really need a soil test that identifies the mineral deficiencies and excesses. There are 92 elements that make up the earth (and the human body) and plants cannot create them if they are not in the soil, so your fruit, vegetables and herbs will lack nutrients that are not in the soil they are grown in. Ideally you need to do a soil test once a year because different plants take out different amounts of each nutrient and the rain and watering can leach out some minerals.
There are two other measures of the quality of your soil that are worth knowing and a good soil test will provide you with these. The first is the level of organic matter in the soil. Historically this used to average 5% but with the advent of the so-called “green revolution” after World War 2, the soils in both the USA & Australia have been degraded and now are commonly only 1.5%. The reason for this degradation is the heavy use of herbicides, pesticides and man-made chemicals which has destroyed the soil’s organic matter. With commercial monoculture systems there is little use of mulch and compost which build the level of organic matter. With regular use of mulch and compost matter you can build up the organic matter in your soil; for example my soil measures over 10% organic matter.
One of our major banks decided they needed a good indicator of whether to make a safe loan to farmers. After much research they came up with the fact that the best measure was the level of organic matter in the farm’s soil!
The other less well known measure of the quality of soil is the CEC or Cation Exchange Capacity. This measure tells you the capacity of the soil to store nutrients. Sandy soil typically has a CEC of only 2 to 4. Heavy clay soils can be as high as 40 to 60. To improve your CEC there are two quick and easy ways. By adding humus or humates or humic acid you can raise the CEC level because humus has a CEC of 250 and humic acid has a CEC of 450. The other way is to use fulvic acid which has a CEC of 1400!! I put fulvic acid in all my liquid fertilizers and in all my foliar sprays.
With all these numbers how do you know what a healthy balanced soil looks like? Professor Albrecht spent his life studying and analyzing soils from all round the world and he came up with the standard which shows that calcium, magnesium and potassium are the most significant elements in terms of quantity. Other elements such as silica, boron and phosphorus are critical but are needed in very small amounts. This is a surprise to many as NPK (nitrogen. phosphorus and potassium) is the most common fertilizer.
Under optimal conditions, soil organic levels are high and there is a large varied population of soil micro-organisms. Nitrogen is a very important element but under these conditions plants use the nitrogen that is freely available in large quantities from the air (which is 70% nitrogen) but which has to be converted to plant available form by soil organisms. There is no need to add nitrogen.
Conclusion: building and maintaining a healthy, balanced soil is an ongoing process, and you really need an annual soil test which should provide all three of the above measures i.e. pH, CEC and the level of organic matter.