# Conditioning Sterilised Soil with Beneficial Bacterial and Fungi

- Link: https://rd2.co.nz/conditioning-sterilised-soil-with-beneficial-bacterial-and-fungi/
- Published: 2019-04-11T14:04:09+00:00
- Author: RSF Admin

_Written by Donald Lester_

Nurseries and greenhouses often recycle their soil by sterilising it or composting
it. And while sterilised soils might be convenient and cost-effective to use, they
can present certain challenges to the grower…

The process of steam sterilisation kills soil pathogens such as soil-borne fungi
and bacteria, [fungus gnat eggs](https://www.planetnatural.com/pest-problem-solver/houseplant-pests/fungus-gnat-control/),
snails, other pest insects, weeds and weed seeds. However, the steam is non-discriminating
in its killing action, so beneficial insects, fungi and bacteria are also killed.
Sterilised soil is just what it says: devoid of life.

The problem is that the balance of good and bad fungi, bacteria and insects is now
lost. Commercial field growers (in particular, berry growers) who [fumigate](https://en.wikipedia.org/wiki/Fumigation)
soil have the same problem. In nature, detrimental organisms are kept in balance
by beneficial organisms. As long as the proportion of good bugs is equal to or greater
than the population of bad bugs, we don’t have a problem. It’s when the bad guys
overpower the good guys that we get a problem.

One way to re-establish balance after sterilisation is to re-introduce beneficial
fungi into the soil.[ Mycorrhizal fungi](https://rd2.co.nz/category/mycorrhizal-fungi/)
are symbiotic fungi that grow on the roots of plants, physically protecting them
from pathogens with a sock-like layer (or, mantle). The fungi dissolve nutrients
in the soil and transport them into the plant roots. In return, the plant provides
finished goods in the form of proteins and sugars to the fungi.[ Mycorrhizae](https://rd2.co.nz/mycorrhizae-the-ultimate-crop-companion/)
fungi spread out into the soil and in effect extend the root system by up to 100
times. There are several species of[ mycorrhizal fungi](https://rd2.co.nz/product/sale-rootella-g-mycorrhizal-fungi-granular-1kg-organic/)
available on the market. Many[ mycorrhizal fungi](https://rd2.co.nz/product/sale-rootella-g-mycorrhizal-fungi-granular-1kg-organic/)
available on the market today contain several species of fungi to take the guesswork
out of which species is needed for which crop.

![Trichoderma](https://www.rd2.co.nz/wp-content/uploads/2019/04/Trichoderma-1024x651.
png "Conditioning Sterilised Soil with Beneficial Bacterial and Fungi 1")

**Trichoderma for Soil Health**

Another beneficial fungus to consider using is trichoderma. Trichoderma is similar
to mycorrhizae in that they attach themselves to the plant roots and spread out 
into the soil to dissolve nutrients for the plant. But Trichoderma has some other
advantages over mycorrhizae. They have as two enzyme systems: cellulose, which breaks
down organic matter, and chitinase, which breaks down chitin (a major structural
component of fungal cell walls). So, typically in the springtime when temperatures
are cooler and the pathogen population is low, Trichoderma will break down cellulose
materials in the soil like sawdust, bark, leaf litter, dead roots, etc. to provide
nutrients to the plant roots. But when the weather warms and pathogenic fungi begin
to grow in the soil, trichoderma produces chitinase and actually parasitizes pathogenic
soil-borne fungi like pythium, Rhizoctonia and others.

![Bacillus subtilis for Sterilised Soil](https://www.rd2.co.nz/wp-content/uploads/
2019/04/Bacillus-subtilis.png "Conditioning Sterilised Soil with Beneficial Bacterial
and Fungi 2")

**Bacillus subtilis for Soil Health**

A beneficial bacterium that has gained a lot of attention in recent years is Bacillus
subtilis, and it is a good biological to add to sterilised soils to regain balance.
This beneficial bacterium produces not only enzymes but antibiotics as well. And
Bacillus subtilis has a tail (or, flagellum) that makes it mobile when the soil 
is moist so it can go on seek and destroy missions in your soil to hunt down and
destroy soil pathogens.

Be wary of products that list many biological agents. Some agents might actually
feed on each other.

And, with many biological species in a mix, how can you be sure there is enough 
of any one organism to be effective at rapidly regaining a balanced population in
your sterilised soil? There are many organisms that live in soil, but not all are
the best competitors with soil pathogens. Stay with species that have a body of 
scientific research demonstrating that they are beneficial to soils.

**Humic acids for Sterilised Soil**

Sterilised soils with low organic matter content might not be able to support a 
healthy population of beneficial organisms. In this case, the addition of humic 
acid might be the solution. Humic acids are a concentrated form of organic matter.
As plant matter decays, it goes through several forms on its way to becoming coal.
Plants die and then become compost, peat, brown coal, Leonardite and black coal 
over time. This progression is marked by a loss of oxygen in the molecules. For 
example, black coal is not an oxygenated fuel. The oxygen in humic acid acts as 
a magnet to nutrients in the soil. Calcium, iron, manganese, magnesium and zinc 
all attach to these many oxygen sites on humic acid and become available for plants
to absorb and use. Not only that, humic acids are an excellent source of carbon 
for the beneficial fungi I mentioned earlier. Moreover, humic acids are known plant
stimulants.

**Wetting Agents for Sterilised Soil**

Sometimes soil becomes difficult to wet after many cycles of steam sterilisation,
kind of like burned soils after a forest fire. One product that can help overcome
this phenomenon is a wetting agent. There are several wetting agents on the market
with many of them being chemically derived or synthetic.

One natural wetting agent is derived from yucca plants. Yucca is a desert plant 
that withstands very high temperatures in very dry conditions. It is thought that
saponins in the plant are responsible for this water-conserving action. Yucca saponins
are routinely added to commercial bulk soil mixes or bagged soil mixes to help aid
in water distribution in pots. A side benefit to this water distribution is that
fertilizers and nutrients carried in the water are also more evenly distributed 
with the addition of yucca saponins. Since the high temperature associated with 
soil sterilisation can alter the chemistry of saponins, it is a good idea to reapply
them to the soil after the sterilization process.

**The Importance of Adding Organic Products after Soil Sterilisation**

All of the materials I have mentioned are available in the market as either conventional
products or organically certified products. By adding the organic versions of these
materials after soil sterilisation, you can save yourself a lot of headaches with
soil-borne diseases and insects, produce a healthier crop and minimize your exposure
to toxic chemicals. And the great thing is you don’t have to wear a moon suit to
apply them!