Good, healthy soil is essential for any permaculture garden. As the growing medium for your plants, it is the foundation on which everything else is based. A healthy soil’s main task, besides giving the plants something to physically be in, is to break down organic matter into forms that can be utilized by plants and other organisms. There are five elements of a healthy soil that interact to enable this function to be performed.
The moisture level in a healthy soil is important for the health of the plants growing in it. The water that is in the soil, either from rainwater or irrigation, provides the vehicle through which soluble nutrients become available to plant roots. While you don’t want soil to become waterlogged, as a general rule, it is preferable to slow the rate that water leaves the soil. Some moisture in a soil will transform from liquid to gas and evaporate into the air. This depends on temperature and atmospheric pressure, and occurs particularly in places with little rain. Adding ground cover plants and preventing direct sun or strong winds attacking the soil can help retain moisture in the soil. To slow the rate of water percolation through the soil – meaning that it takes nutrients away from plant roots before the plants have had a chance to access them – add more organic matter such as compost to the soil.
Of significant importance in the retention of moisture in the soil, is the mineral composition. This refers to the proportions of different types of particles in the soil. A soil with a larger proportion of clay minerals, which are very fine, drain more slowly and hold water well, but form a hard, impenetrable surface in dry conditions. Soil that has a greater proportion of larger particles, such as sand, drains more quickly − which can be good for areas of high rainfall. For most areas, a mixture of the two is preferable, allowing for a medium level of drainage, which means nutrients are still available to plants but the soil does not become waterlogged. However, the ideal type of soil for your permaculture site will depend on the specific weather conditions that act upon it.
The three primary gases present in a healthy soil are oxygen, nitrogen and carbon dioxide. Plants use carbon dioxide to help with photosynthesis, a byproduct of which is oxygen, which is then used by animals in the soil. Nitrogen is an essential gas for plants to build proteins, perform photosynthesis and form DNA. When the levels of these gases are in equilibrium, the soil is healthy and plants and microorganisms thrive. To ensure a healthy level of gases in the soil, there needs to be an effective exchange of gases between the soil and the atmosphere. This exchange ensures that there is an adequate supply of oxygen in the soil to allow plants and microorganisms to thrive. Without the exchange potentially damaging levels of other gases, such as sulphur dioxide, can build up. The effectiveness of the exchange of gases is linked to the structure and composition of the soil, and takes place via two main processes.
Mass flow refers to the exchange of gases that takes place after rainfall or irrigation. As the water percolates through the soil, gases are displaced and enter the air. Conversely, when water from the soil evaporates, atmospheric air enters the soil. Diffusion, the more common form of gas exchange, involves the exchange of gases between the soil and atmosphere depending on the respective pressures of the gases. So, if the pressure of, say, carbon dioxide in the atmosphere is greater than that in the soil, it moves into the soil to create an equilibrium, and vice versa.
Organic matter is the magic ingredient in a healthy soil. It gives the soil nutrients, can help the mineral composition (making clay soil moreopen, and helping sandy soils preserve water and nutrients), will add nitrogen to the soil, and affect the retention of moisture. The organic material also provides food for the microorganisms. Thus, you really can’t have enough organic matter in your soil. There are many ways to increase the amount of organic material on your plot. Composting turns food scraps, garden prunings and anything else that was once living into nutrient-rich humus that can be added to soil around plants. Cutting back crops such as barley and wheat and leaving the cut plants on the ground will allow them to break down directly into the soil, while mulching offers the duel benefit of a slow release of organic matter from the mulch itself (which can be anything from branches and leaf litter to woolen carpet underlay or old jeans) and the breakdown of weeds beneath the mulch as they are deprived of sunlight, and then rot into the soil.
When there is a good balance between the gases and water levels in the soil, and there is sufficient organic matter, microorganisms will be abundant in a soil. This makes it healthy, as these organisms – bacteria, fungi and insects – have many positive effects on the soil to keep it in good condition. They break down nutrients in the soil and so make them available to plants. They break up the soil, providing space not only for plant roots but also air and water to penetrate the soil. And when they die they become part of the organic matter, returning their nutrients to the soil in the cycle of life. The more microorganisms – and the greater range of species – the better, as the ecosystem will become self-regulating, preventing any build up of pest populations.
All five of these elements are interacting all the time. Initially, it can seem daunting to think that you need to balance all of them correctly to ensure your plants survive and thrive. However, remember that nature will naturally try to find a way to achieve that balance, and by observing and replicating nature, it shouldn’t be too had to create ad maintain a healthy soil.