If you are serious about gardening, you need to get as much organic material into your soil as possible. All things being equal, soils with high levels of organic matter will have less impact from pests and diseases, particularly soil based ones (such as root knot nematodes).


Don't Be Fooled

All too often people will purchase bagged soil and expected to get good results, particularly when they have purchased a so-called premium organic mix. Without life supporting organic matter, the fertilisers in the soil will quickly be used up or washed away. Once this occurs plants may struggle to survive, let alone thrive.


Organic Matter

Incorporating organic matter into the soil can have several outcomes, affecting the physical, chemical, and biological balances in the soil. It can change:

  • the amount of nutrients that is available to soil microbes, fungi, animals, and plants;
  • the number and type of organisms present in the soil; and
  • the way the soil sticks together (soil aggregation)

All of these changes are related to the way organic matter is decomposed when it is incorporated into the soil and to the particular type of organic matter used.


The Process

When organic matter is incorporated into soil, the larger organisms like mites and soil animals break it into smaller pieces. Then the fungi and bacteria start to decompose it by secreting enzymes. When the enzymes break the molecules into smaller sections, the bacteria and fungi can use some of the energy or nutrients released for their own growth.

If there are nutrients that the microbes do not use, they will be available for other soil organisms or plants to take up and use. When microbes die, their cells are degraded and nutrients contained within them become available to plants and other soil organisms.

Microbes can access nitrogen in the soil more easily than plants can, so the plants sometimes miss out and the plants can become nitrogen deficient. This is why incorporating organic matter into soils can change the amount nitrogen (and other nutrients) that is available to plants. This will be a short-term effect that happens when soils do not have high levels of organic matter and soil microbes.


The Benefits

If the number of fungi and bacteria associated with the breakdown of organic matter increases, there may be some improvements to the soil structure. Adding organic matter can also increase the activity of earthworms, which in turn can also improve soil aggregation. If organic matter is retained in the soil, the number of microbes in the soil increases. This is because the microbes can use the organic matter as a source of energy and so they can grow and multiply.