10/06/2017
Soils
With soil becoming one of our most precious resources, preserving and building soil are becoming essential knowledge for any sustainable garden project. Building soil requires feeding the soil micro-organisms organic matter, which can come in all different varieties.
Six Properties of Soil
Having a good understanding of the soil on your permaculture plot is key to making it productive. The soil, as the medium in which plants grow, is the bedrock of your site. Soil can be changed over time, and plants can adapt to those changes, but having the knowledge about the make-up of your soil will make your planting and soil treatment more effective.
The properties of the soil were originally determined by the material that went into its original manufacture – the rocks which in the past were weathered down into soil particles. However, agricultural and permaculture practices can also have an impact. Here are the major properties of soil.
Texture
The texture of the soil refers to the proportions of three major materials within it: sand, clay and silt. Particles of these materials are of differing sizes, and their presence in the soil will affect the soil’s ability to retain nutrients and moisture. Sand particles are the largest of the three, so a soil with a higher proportion of sand in it has more space through which water moves, meaning it dries out quickly. Clay has the smallest particle size of the three, and so a soil heavy in clay will retain water well, but have a slower rate of infiltration. Silt particles are somewhere in between. As well as affecting moisture retention, the soil texture directly influences the soil’s fertility, because they provide surface area to which nutrients can adsorb (the process by which molecules adhere to a surface). Clay particles provide more surface area for this to occur than sand particles. Soil that has a good proportion of each of the three materials is an ideal growing medium, and is called loam.
To get a basic idea of the texture of the soil on your plot, simply pick some up and feel it. A sandy soil will not adhere into a ball and have a gritty feel. A clay soil, by contrast, feels smooth and almost plastic to the touch. Loam will have a springy feel.
Structure
Linked to the texture is the structure of the soil. This refers to the way the particles of sand, clay and silt aggregate together (form clumps) and the spaces that form between and within them (called pore spaces). The spaces between aggregates are larger than those within, and as such are the key to the soil’s drainage ability and aeration. The spaces within aggregates, being smaller and more tightly packed hold water. As with many things concerning soil, a good balance is required to create a decent soil. Stable aggregates combined with plenty of pore spaces are best. Adding organic matter will help do so.
Biology
The biological property of the soil refers to the amount of microorganisms that are active within it. These include everything from earthworms and insects to fungi and bacteria. In a healthy soil, the number of organisms living in the soil will be high, which in turn helps to keep the soil healthy, by processing nutrients and improving soil structure, which helps plants to grow. Healthy soil biology also means that populations of species are kept in balance, with some organisms predating on others so they do not get too high. The amount of organic matter available, adequate soil moisture, as well as good drainage and aeration of the soil affects the biological property of the soil.
Cations
Here’s the science bit. Cations are positively charged ions of nutrients that are in solution. Basically, for plants to access nutrients in the soil (such as nitrogen, phosphorous and potassium, those nutrients need to be in a soluble form, mixed with water. When the atoms of the element are in water they become electrically charged, either negatively (called an anion) or positively, the cations. The positive charge allows the cations to adhere to soil particles (the process of adsorption) from where plant roots can access them.
pH
A bit more science. The pH level of the soil refers to the concentration of positively charged hydrogen ions in the soil moisture. With more of these ions, the soil becomes acidic, while fewer indicate an alkaline soil. The pH of a soil is measured on a scale of 0 to 14 (the lower the number, the more acidic the soil), and the position on the scale is likely to affect levels of essential nutrients in the soil. For instance, a soil with a pH level lower than 6 is likely to be deficient in potassium, calcium and phosphorous, while a soil with a pH of higher than 7 will probably lack sufficient iron, zinc and copper for healthy plant growth. The best way to ensure a healthy pH in your soil is the addition of organic matter. This will provide nutrients that the soil may lack, as well as protect plants from the effects of excess acidity or alkalinity. If you have a very acidic soil on your site, the addition of agricultural lime can help lift the pH level. However, you can also plant species that require certain pH conditions to thrive. Blueberries, for example, grow well in acidic soils, while the brassica family of vegetables (such as cabbage) prefer alkaline soils.
Salinity
The water within a soil, combined with the nutrients in solution within it, affects the salinity of the soil. If moisture levels in the soil are low, particles of sodium, calcium, magnesium, and potassium increase, meaning the soil becomes more saline. This can be exacerbated if, due to lack of moisture at the surface, plants draw up moisture from the groundwater that, in turn, evaporates, leaving the salts behind. If the salinity of the soil increases too much at the surface, it will negatively affect the growth of plants within it. Ensuring soil receives and retains sufficient moisture (through diverting runoff to dry areas, mulching to prevent excess evaporation, etc.) ensures salinity does not become a problem.
As with many things in permaculture, none of these properties stands alone; all are impacted by changes in the others, and all are in an ever-evolving relationship with the plants that are growing in the soil. By understanding the properties of the soil on your site, you can make sure that you are planting species that suit the soil conditions, and that you are aware of how making changes impacts upon the soil system.
Five Functions of Soils
Soil is amazing. It is the medium in which much plant and animal life depends. It is also a dynamic system, changing according to the environmental factors that act upon it, and the influence of humans. It forms part of an intricate ecosystem, interacting with the plants and organisms that live in and on it, the rock beneath it, the topography of the landscape on which it sits and the climate around it. There are several functions that soil performs.
Support
On a basic level, soil provides a medium in which plants can grow. It serves as an anchor for the plant roots, and acts as a holding ‘tank’ of moisture that the roots can access when they need to. A healthy soil, with sufficient moisture, a good balance of gases, and plenty of organic matter is the ideal medium for plants to grow in, and permaculture gardeners have a primary focus on making sure the soil is hospitable to the plants they wish to grow.
The degree of support and anchorage that the soil gives to plants will affect which species will thrive in particular soils. Several variable properties of the soil that affect plant growth include how fine or coarse the texture of the soil is, the degree of aeration, the proportion of organic matter, and the ability to retain moisture.
As an anchor for plant roots and as a water holding tank for needed moisture, soil provides a hospitable place for a plant to take root. Some of the soil properties affecting plant growth include: soil texture (coarse of fine), aggregate size, porosity, aeration (permeability), and water holding capacity.
Water Provision
When moisture falls on the land – either from rain, snow, frost and mist, or from irrigation techniques – the soil absorbs and stores it. This water is then available for both plant to access through their roots, and for the microorganisms that live in the soil, who, like all life on earth, need water to survive. The water also acts as a solvent in which nutrients in the soil can be absorbed by plant roots. This ability of the soil to store moisture is particularly useful in locations where precipitation is intermittent. Increasing the water-holding capacity of your soil also helps preserve water, as less irrigation is needed.
Because gravity is always working on the water, it moves down through the soil. Any moisture that is not used by plants or microorganisms, or does not evaporate from the surface of the land, eventually finds its way down to the water table. The rate at which moisture percolates through the soil depends primarily on the structure. Soil that is predominantly clay particles slows the drainage of water more than soils with more sand particles. Sand particles leave more space between themselves, which gives space for the water to trickle through.
There are several things a permaculture gardener can do to enhance the ability of their soil to retain water. Adding organic matter improves the structure of the soil and promotes more plant and microorganism growth, both of which use water to grow. Planting ground cover crops reduces the rate of moisture evaporation from the surface of the soil, while contouring the land, by creating swales and other water-holding features, is another way to slow the movement of water off the land.
Habitat
Healthy soil is veritably teeming with life. It is alive with everything from bacteria and fungi to earthworms and beetles. These microorganisms are the primary engines of decomposition in the soil, turning dead and rotting materials into organic matter that they, and plants, need. Like the majority of life, soil microorganisms require some basic things to live, namely air, food, water and a habitat. A healthy soil provides all these and enables the organisms to survive and thrive.
Organic matter provides the organisms with carbon, which they convert into energy, so keeping an abundant supply of organic matter on the soil, through composting and mulching, is a beneficial activity in a permaculture garden. This will also improve the structure of the soil, allowing air to pe*****te and so providing the microorganisms with the gases they need for respiration (most organisms are aerobic and require oxygen, but some can survive without oxygen, and are called anaerobes).
Digestion
You can, in one way, conceive of soil as a vast stomach. It is a digestive marvel. Healthy soil decomposes any organic matter that falls upon it – dead plants and animals – into simpler mineral forms. Living plants and animals then use these resultant forms as energy in the creation of new growth. The primary actors in this decomposition process are bacteria, fungi and insects that live in the soil.
The rate at which these microorganisms break down organic matter is dependent on several variable factors. They require sufficient water and oxygen to be present in the soil, and both the soil temperature and its physical structure will impact upon their activity. Another significant factor is the chemical make-up of the matter to be decomposed. Matter with a high level of nitrogen tends to be decomposed more quickly.
One of the primary elements in organic matter is carbon. The microorganisms use this carbon as an energy source. Because of the soil’s ability to hold a large amount of carbon, keeping soils healthy is an important part of limiting the impact of climate change. When soils are mistreated, by removing the rich surface topsoil, for instance, that carbon is released into the atmosphere, and carbon emissions are a leading cause of global warming. So it is beneficial not only for the plants and animals, but also the planet, for permaculture gardeners to look after their soils.
Respiration
Plant life is often referred to as the lungs of the world, providing animals (including humans) with the oxygen they need to survive. If that’s the case, you could conceive soil as the diaphragm. The soil interacts with the atmosphere around it to create a beneficial balance of gases within both. Gases including nitrogen, oxygen and carbon dioxide flow into and out of soil so they remain at levels that support the life in the soil. A healthy soil, with lots of organic matter, sufficient moisture and variety of plant life, helps maintain the correct balance of gases.
Soil is the medium that thrives plant and animal life. Know more about the importance and functions of soil for a healthy ecosystem.
