What Is Soil?
November 7, 2016
This article was written by Jeroen Kateehm. It is republished here from Garden Culture Magazine, Issue 5, where it appeared under the title, “Soil Is Still The Stuff To Grow On”.
Your yard is full of it. But what is soil? Why is it that in some locations soil is able to grow great results easily, and in others, gardening is so difficult? Before you give up on your soil and decide that the more exact science of high-tech gardening is the only way to succeed at growing, there a few things you should know…
Even though hydroponics continues to grow in popularity, soil is still the stuff to grow on. There are many types and compositions of soil. It’s no news that having healthy and fertile soil is important for plants to grow efficiently. Taking care of your soil isn’t that complicated, but it’s important to understand the principles that govern soil health if you’re going to understand your garden and improve on your gardening skills.
Soil itself is not living per se, but an assortment of things, some of which are alive. Dead soils do exist, but a healthy soil should contain a lot of life. To keep it simple, soil consists of three things; live parts, dead parts, and parts that have never been alive. Caring for soil is managing life. This is not an office job, but depending on the amount of study and calculations you put in, it can become one. Generally speaking, it’s ‘dirt simple’… pun intended.
Since soils form over long periods of time, changes are not usually seen in the blink of an eye. It’s easy to say up front what the hardest part will be: gaining experience, the ability to see what is going on and recognize any problems before they get out of hand.
The dead parts of soil make up its structure. Most of this structural material is rocks of various kinds. These rocks, over millions of years, have weathered and broken down into smaller fragments. The texture of a soil is mostly determined by the size of these fragments. The fragments are commonly graded in three sizes. Sand being the biggest, medium-sized mineral particles called silt, and the smallest mineral particles known as clays.
Each of these particles has different effects on how a soil behaves. Soil functions like water and nutrient retention, the ability to hold temperature, or support root growth – are all determined by this composition.
Sand, for instance, lets water pass through more easily than clay does. The finer particles in clay are better at storing water, but it’s also much more dense. This makes it harder for roots to penetrate, and among other things it’s less porous, allowing less air into the soil, and between the roots.
Silt, being an intermediate size, also has intermediate characteristics. Soils are usually made of these three elements in combination. Agricultural scientists and agencies use a triangle graph to classify the texture of a soil. (–For instance, the UK-ADAS and USDA textural triangle.–)
Laboratories use extensive methods to accurately measure the mixture of particles in a soil. There is a slightly less accurate do-it-yourself method too.
Apart from rock derived particles, soil can contain other things that change its texture. Organic matter is an important component of a healthy soil, although quite often limited in its amount. Soils that have depleted their organic matter will become less fertile, quickly. Organic matter, although not high in nutrient concentration, is important in regulating nutrients.
Humus – the end product of composted plant life – has chemical properties helping to free up minerals for plant uptake. Humus provides a lot of other benefits for plant life and soil health, but without additions of new organic matter, it won’t last.
As is extensively covered in this magazine, soil is full of beneficial life. Not only do plants support each other in certain cases, but other life forms, such as the bacteria and fungi that play a vital role in healthy soils. In forming, and in maintaining structure.
When soils form naturally, it is through interactions of many unique life forms. Bacteria play a role in breaking down plant matter from the first pioneering species. Fungi provide symbiotic relationships with plants to aid them in harsh conditions, such as droughts. Plants help absorb nutrients and store these in their tissues. Because of this, soils grow slowly from infertile lands to nutrient-rich soils with improved qualities.
The type of plants that grow naturally in soil is usually a good indication of the health and type of soil you’re dealing with. Plants that need a lot of nutrients will be outcompeted by others. Plants requiring a lot of water will do poorly in sandy soils. Most of these things are obvious, but realizing that requires experience.
WHAT IS SOIL MAINTENANCE?
How to maintain your soil is one of the most hotly debated topics ever. Mankind has been growing crops for thousands of years, and the start of this is often marked by the plow’s invention. The plow has been in use for longer than almost any other tool humans have invented. However, are they essential? There are a few reasons why plowing might be unbeneficial in all cases. The soil life is disturbed. Natural channels for water to flow through are broken, which changes the permeability and water absorbing capabilities of a soil. Plowing increases the quality of a soil in the short term, but quite possibly, and if not managed carefully, damages it in the long term. But it’s a hot issue.
Maintaining the amount of organic matter in a soil can bring some complications with it. The easiest solution to this is simply to let surplus plant material decompose on top of the soil, or plow it through the top. While this is easy, many people find that this method attracts more pests. An indirect method is to feed compost to the soil, in this way the risk of pests is lowered. Another hot topic is whether or not to plow through these soil additives, specifically with potted plants or grow-beds.
Many choose to completely remix their substrate after a growing cycle by breaking up clumps, and adding new materials to upgrade the soil. Others choose disturbing their soil as little as possible, only removing stumps or other debris that won’t compost fast enough. The difference is that by not mixing up the soil completely a natural concentration gradient will form, even inside the pot of a potted plant. There are good arguments for both sides, so it’s up to the growers’ preference. Generally though, it’s advisable to disturb a healthy soil as little as possible, what good would it do?
The way nutrients behave in soils is greatly dependent on the soil texture and health. Sandy soils have a lot lower buffering capacity in this regard. Mobile nutrients are easily washed out, creating a nutrient imbalance. At the same time pH levels are also more susceptible to swinging up and down. Humus, clays, and things like volcanic rock, can help with buffering these elements making the ups and downs less violent. Timing of nutrient application, and the relative input amounts are important to consider. Soils that have a low buffering capacity will need more regular application, and smaller amounts of nutrients.
The key to understanding how to maintain a healthy soil is to understand what is going on inside it. Every soil is different and requires different maintenance. Learning how these processes work is rewarding.
Healthy soils are the backbone of a productive garden. Take care of it and it will take care of your plants.
DIY SOIL TEST
Not sure what kind of soil are you dealing with in your garden? This will give you some clues.
- Take a sample of soil.
- Pulverize it until you’ve broken up all clumps.
- Put a layer of the pulverized soil in a glass jar.
- Fill the jar with water, and put on the lid.
- Shake the jar.
- Let the particles settle on the bottom.
The biggest particles will settle first, so the bottom layer will be sand. The middle layer is the silt layer, and on top is clay. It can take quite a while, but when everything settles you can measure the individual layer proportions, and calculate what kind of soil you’ve got. To help with getting an even distribution after shaking, add a small amount of non-foaming detergent.
TIP: Soils aren’t always the same all over the yard. Test a few spots. How many? How big is your garden?