Good soils in gardens are not automatically there, houses being constructed on varying soil types. But what does a good soil consist of, what are the farmers or agronomist looking for? Lets look at the basics of the soils.

Soil should combine moisture, air, soil particles, humus and micro organisms. The percentages will alter but the best combination would be 25% moisture, 25% air 45% soil particles and the remaining 5% humus and micro organisms, humus being the major ratio of the 5%. The combinations will influence the soil fertility and the potential for the good growth of the plants.

Soils contain particles of differing size, stones of any size, but the smaller constituents of soil are, clay which is a particle small than 0.002 mm, silt which would be between 0.002 and 0.06 mm, and sand being anything over the size of 0.06 mm. All have differing characters as constituents with clay being the most important. The ratio between surface area to volume is large, and this increases it capabilities to keep and attract positive ions containing nutrients. Clay is flexible and easily absorbs water, but it hardens when dry and can cause anaerobic areas within the soil structure. Rehydration of clay does not always increase oxygenation so it can become problematical. Silt and sand support the drainage and oxygenation of the soils and facilitates the areas for the penetration by roots. So a good mixture containing all three is desirable, the combinations dependant on the plants grown. Look out for compaction that can come with high clay content soils, sand is incapable of being compacted so keep the sands high.

The ecosystems supported within the soils humus are responsible for the health of the soils. This humus will mix with the larger particle soils and cause darkening colours. Broken down organic matter by the micro organisms, assisted by fungi and bacteria becomes humus, a requisite for the ecosystems to exist and survive. Distribution of the humus within the soil structure is by small insects, earthworms and ants, and the burrowing and tunnelling of these insects aerates the soil.

Humus, a biochemical substance, is largely overlooked by the gardener, and attempts to replace it with a synthetic substances unsuccessful. It is a vital constituent of a good soil, its moisture retaining capabilities, as well as storage of nutrients at root zone level are important for plant growth. It is the main supplier of Nitrogen and Carbon to plants, it enhances the soil and is normally found in the upper regions of the soil structure, found by the millions in small samples of the mixtures.

Earthworms and insects are a necessary constituent of good soils, they aerate the soils, facilitate moisture movement and aid in the breaking down of organic matter. This semi digested organic material becomes humus, so again they assist to make the soil quality good .

Soil pH, a nightmare if incorrect, plays an important part in soil structure and its ability to support plants. The level of pH will affect the nutrient uptake of the plants, as well as the reactions of a chemical nature, inorganic and organic that exist within the structure.

Soil colour varies, and is dependent on the mineral composition, and this colouring is a source of information for the gardener. Red or yellow soils are indicative of oxidization of iron or aluminium. Black soils, high levels of humus, grey, high iron leaching, greenish or blue-grey, high water tables, and brown, combinations of organic matter and iron oxides. High calcium’s show up as white, but these are generalisations as many factors can influence the colour. Soil colour is a tool used by agronomists or Golf Course Superintendents, for diagnoses of problems with the grasses. Grass colouring or discolouration and soil colour go hand in hand.

This is the basis of good soils and hopefully will help when determining the requirements to improve yours.

A good soil will always have a great nose and will have the aroma of cleanliness, it should smell good enough to eat. Why is this the case? I have no idea, but humic acid and humic products do emit a clean odour, so use your nose if the soil smells good, the chances are it is good.