A Primer On Soil Science
A Primer On Soil Science
Excerpt from January 2011 Tree Tips Newsletter
For this January newsletter I thought it may be a good time to talk a little about soils and how they affect your plants. Without a good understanding of some basic principles about soil science growing healthy trees can be quite difficult and frustrating. It is important to understand what type of soil you are dealing with and it’s characteristics so you can better manage your cultural practices.
The first thing to understand is that for the most part you are pretty much stuck with the soil that is native to your area. It is possible to make some minor alterations but it is important to accept that the soil you are dealing with has been evolving for approximately four and a half billion years and it is not likely that you can do anything in one afternoon to radically change the characteristics of your local soil.
The five things that affect the evolution of your soil are:
- Parent Material: bedrock and organic material, imported material from glaciers, volcanoes and flooding
- Climate : heat, rain, ice, wind and sunshine
- Organisms: plants and animals – both micro and macro
- Topography: low lands, slopes, elevation
As time progresses all of these elements come together to form what we call soil. For instance, if you live in a high precipitation area with moderate temperatures you will naturally have more vegetation and animal life thus more organic matter than if you lived in the desert with low precipitation and hot temperatures. You would also expect more parent material from sedimentation and run off. In colder climates, because of freezing and thawing, you get a more rapid breakdown of the bedrock. Each of these five elements react with one another in a multitude of combinations that ultimately form soil.
How they interact will determine whether you have sandy soil, a loamy (silt) soil or a clay soil. The organic matter will determine if your soil is light or dark in color, it’s pH, and it’s ability to bind with other elements as well as it’s water retention capabilities.
The terms sandy, loam (silt) and clay refer to the relative size of the particles that make up the soil. Sand particles are the largest, loam particles are in the middle and clay particles are microscopic. Size is important!
Because sand particles are relatively large they have large pore spaces between them which aids drainage but lacks the ability to bind or hold on to each other and other elements. This means that it will require more water and more nutrients because of leaching. On the other hand, clay particles are microscopic and have small pore space which inhibits drainage but encourages a high binding capability. This means they will need less water and less fertilization. Loam particles are in the middle range of the other two and share the characteristics of both and are generally considered to be the best for plant growth. Sandy soils come in second because you can better control with cultural practices than if you had a tight heavy clay soil that does not drain or allow for the movement of water, air and nutrients.
Another important characteristic is the soils pH. This is the factor that measures the soils relative acidity or alkalinity. Soils with high organic matter content are usually slightly acidic. Parent material also plays a part in the pH factor. The pH scale goes from 0 (highly acidic) to 14 (highly alkaline) with 7 being neutral.
A slightly acid soil with a pH of around 6.5 is considered most desirable because it is in the range where elements such as Iron, Zinc, and Manganese are the most soluble and thus available for plant uptake.
Another important characteristic is the amount of salt present in the soil. Overall, salt has a negative impact on both the physical attributes of the soil as well as a negative impact on plant cells. A high content of salt is the cause of deflocculation which is a big word that basically means it prohibits the particles of the soil to bind together. When this happens you lose all the pore space which in turn prevents drainage as well as the movement of air and nutrients. Another problem with salt is that because it is soluble it eventually gets picked up by the plant and if the per cent of salt content in the cell becomes to high it will kill that cell.
Salt can originate from the parent material or accumulate from irrigation water with a high salt content. Fortunately, if you have adequate drainage, you can leach it out of the soil profile with deep watering and get it below the root zone.
Everything I have just discussed has a bearing on how trees take certain elements out of the soil. So to end this I need to toot my own horn here. By using systemic implants you virtually eliminate all of the soil characteristics that have a negative impact on nutrient uptake. The Systemic Implants put the required element or elements directly into the vascular tissue so you do not have to be concerned with drainage, leaching, solubility, pH, salt content, etc., etc. Toot Toot!
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