Here is the text I created for my audio narration to the video “Plant ID: Soil”:
Soil is one of the most vital aspects of a plant’s environment. Obviously all aspects combine to support life as we know it, so take away sunlight or water or oxygen and most life will struggle or soon die.
What makes soil so important is that most plants get the materials they need to survive through the function of their roots.
Plant roots get all of their oxygen, water, and most of their nutrients from the soil. In return, these materials support a system of the plant which balances effective production and growth.
For example: without a healthy interaction between the soil and roots, there would be minimal resource for leaf production.
Without an effective amount of leaves or leaf function, photosynthesis would be minimal or inadequate, which means sugar or energy production suffers, ultimately leading to no support for root maintenance or development.
And now coming full circle, without support for proper root function the plant cannot correct its deficient photosynthesis, and is destined to fail and soon die.
Since roots are essential for the overall health and vigour of most plants, that means the soil is equally essential.
But keep in mind that in the bigger picture all components of a plant as well as its environment come together to provide a healthy effective operation.
Also keep in mind that soil provides the plant with anchorage and support; it is a foundation for physical structural stability and helps the plant maximize size and space.
Let’s start with some basic identification of soil:
All soils are mixtures of different sized particles and/or inorganic material, living organisms, organic matter, dissolved nutrients, water, and air.
The general ranges of particle size are:
gravel, which is larger than 2mm,
sand, which is between .02 to 2mm,
silt, which is between .002 to .02mm,
and clay, which is less than .002mm.
The particles of soil are mainly described in terms of texture and structure.
Texture describes the proportions of particles in the soil.
For example: a soil sample that has a large amount of 1mm particles that easily move and separate between each other or do not stick together, and can be easily seen as individual grains, would be classified as sand or some sandy combination.
On the other hand, a soil sample that has particles less than .002mm which cannot be easily distinguished by individual grain, so that the sample feels and appears to be a cohesive clump or lump of material, would be classified as clay or some clayey combination.
Sandy soils do not hold water well, and as a generally porous material they tend to have low nutrients and organic activity.
Sandy soil is prone to temperature extremes, run-off, leaching, and erosion.
Clay soils tend to have slow or poor water infiltration, and as a generally compact lumped pedal structure they retain what materials they do have.
Clay soils have a greater chance of containing nutrients and organic activity, but can also be a difficult soil for root growth if too compacted.
A generally equal proportion of sand, silt, and clay is classified as a loam soil. As you can imagine, loam soils have a good balance between particles, air, and water for root growth.
There are numerous combinations of sand, silt, and clay soil textures and structures.
Structure describes arrangements of particles and the combined interaction and behaviour with other soil material.
When particles act and move individually, and do not stick together or separate easily, their structure is described as apedal.
When particles stick together, forming clumps or aggregates of material, their structure is described as pedal.
These clumps of material can also be called peds.
Decayed organic material mixed with particles forming the aggregate or ped is also described as humus.
When it comes to structure, a crumb clumping is usually a good arrangement of particles, other soil material, and pore spaces.
The pore spaces around particles are important because that is where air collects and roots have room to grow, while water is held within the aggregate material of the soil.
The main root zone in soil goes down to about 300mm.
The deeper we go down into soil the less oxygen is present, vital aerobic activity becomes anaerobic. We shouldn’t find much organic material at these depths. The anaerobic breakdown of organic matter can produce gases which are toxic to roots and can also compete for oxygen.
-Living organisms in soil can be the usual soil life you have seen such as earthworms, snails, and insects, as well as micro-organisms such as fungi and bacteria.
Living organisms help break down many of the other usual materials that make-up soil, such as organic matter.
-Organic matter is non-living and decaying material such as leaf litter, dead vegetation, wood from fallen trees, as well as the remains of animals.
Living soil organisms help break-down the organic matter into minerals and nutrients useful to plants.
A healthy interaction and balance between living organisms and organic matter helps maintain good growing and living conditions.
-Dissolved nutrients occur as organic matter continues to break down, releasing minerals that made-up the organic matter or result from chemical changes. These mineral nutrients dissolve with water in the soil and can be absorbed as ions by the plant roots.
The most important nutrients or the nutrients a plant needs in large quantities are described as macronutrients. The macronutrients are:
Nitrogen, Phosphorous, Potassium, Calcium, Magnesium, and Sulphur.
The essential nutrients a plant needs in small quantities are described as micronutrients. The micronutrients are:
Iron, Manganese, Copper, Zinc, Boron, Molybdenum, and Cobalt.
Hydrogen, Oxygen, and Carbon are also major essential elements but are not absorbed by the roots as ions.
Keep in mind that these are not the only nutrients a plant uses, but they are the essential ones. For example: Chlorine and Sodium are also valuable to a plant.
-Water is critical for almost all processes both inside and outside of the plant. Water is necessary for the roots to absorb nutrients; it helps make materials soluble and acts as an agent for interaction/reaction.
-Air represents both Carbon Dioxide and Oxygen. Roots need air in order to take-up water and nutrients. Oxygen is vital for root growth. Air fills the pores between soil particles and allows room for roots to grow/helps maintain space for roots to occupy, also allows for the movement of other materials in the soil.
The acidity and alkalinity of soil is important because of its effect on the availability of plant nutrients, as well as other vital plant needs and functions such as the conditions for disease or unfavourable conditions for important microbes.
Varying acidity and alkalinity levels can inhibit the decay or breakdown of organic material and the release of nutrients into the soil as well as inhibiting plant roots from absorbing nutrients.
The pH scale is a range of hydrogen ion concentration in a soil solution sample, where particular concentrations correspond to an acid or alkaline soil.
The pH scale goes from 1, which is very acid, to 14, which is very alkaline. 7 is the halfway mark and represents neutral.
Most soils range from pH 3 to 10.5
General acidity soils range from pH 4.5 to 5.5
Most plants prefer a pH around 6 to 6.5
Iron is most available between the pH range of 5 to 6, Nitrogen between 6 to 8, Phosphorous between 6.5 to 7.5.