# Soil …NOT just dirt

- Link: https://rd2.co.nz/soil-not-just-dirt/
- Published: 2019-04-16T14:18:28+00:00
- Author: RSF Admin

 

Properties of soil are quite complex made from a combination of both living and 
nonliving materials, water and air; all of which are of equal importance in supporting
plant life. A two-way relationship exists between plants and the soil. The existence
and importance of soil organisms in agricultural production are of equal importance.
Soil organisms comprise 4 main activities:

 1. Organic Matter decomposition & nutrient cycling
 2. Interaction with plants affecting both health and production
 3. Maintenance of soil structure
 4. Biological degradation

Carbons and residues expelled from the roots of live plants provide sources of energy
and nutrients for the organisms, which decompose organic matter, improve nutrient
availability and soil structure, transmit and prevent disease and degrade pollutants.
Soil organisms can increase or reduce agricultural production, likewise agricultural
practices can be both beneficial and detrimental to the soil organisms. As with 
mineral uptake a natural balance exists.

![dead-unhealthy-soil](https://www.rd2.co.nz/wp-content/uploads/2019/04/dead-unhealthy-
soil-300x208.png "Soil …NOT just dirt 1")

Access to carbon, a core element of organic matter and vital energy source for soil
organisms and plants, is gained through decomposition. The population of micro-organisms
is the main engine for organic matter decomposition and nutrient release. Soils 
with high levels of organic matter support a greater number and more diverse range
of microorganisms whose activity within the soil makes nutrients available for each
new generation of plants. Organic matter thus supplies the “life of the Soil”. Mineralization,
the conversion of organic matter by soil organisms to available nutrients, is the
key to soil fertility. While decomposing organic matter to obtain carbon, microorganisms
release other nutrients into the soil and air. These may be: soluble and leached(
e.g. nitrate [NO_(3)]), volatile and lost to the atmosphere (e.g. nitrogen as N_(
2) & N_(2)O, sulfur as H_(2)S) or readily available to the plant (e.g. nitrates,
phosphates and sulfates).

In order to increase the up-take of a specific nutrient, many plants form mutual
relationships (symbioses) with soil micro-organisms. Examples of symbiotic relationships
include: legumes with the bacteria_ Rhizobium_ sp. to fix atmospheric nitrogen gas,
and _Mycorrhizal_ fungi with most plants to absorb water, nitrogen, phosphorus and
other nutrients from the soil. Microbial activity is the natural life cycle of the
soil system, in which nutrients become available to plants. Therefore, a soil with
no microorganisms can be considered a dead soil. Soil organisms act as bio-filters
by degrading soil pollutants. Many agrochemicals are broken down by soil microorganisms
however their effectiveness will be modified by the soil environment. Toxic elements,
e.g. arsenic, chromium and mercury, can be ‘locked’ in the soil by microbial activity,
preventing further pollution.

 Disease causing organisms (pathogens) affect crop and plant growth in two ways:
by invading the plant cells, or by the production of poisonous metabolites and excretory
products. By invading the root, to obtain nutrients, pathogens disrupt the root 
performance or reduce root length, breaking down tissue by rotting. The degree of
root damage generally relates to the number and type of pathogens present which 
in turn will be directly related to the presence or absence of a well balanced microbial
diversity.

![root-damage](https://www.rd2.co.nz/wp-content/uploads/2019/04/root-damage-300x199.
png "Soil …NOT just dirt 2")

 Twenty to thirty-five per cent of all carbon energy or exudates (simple sugars,
produced by photosynthesis) are pushed out of the roots into the soil to attract
bacteria and fungi that will protect the plants from pathogens. This is a natural
condition which can be disrupted by excessive chemical applications, often resulting
in pathogenic species becoming dominant. Soils with high levels of organic matter
and organism activity, or a specific group of antagonistic microorganisms, seem 
to prevent more aggressive pathogens from taking hold. These soils are termed suppressive
soils.

The idea of using one microorganism against another, the predator against the prey,
offers an environmentally compatible and intellectually appealing approach for the
control of plant diseases (Erwin and Ribeiro 1996).

The success of biocontrol however largely depends on the type of antagonist as well
as the basic knowledge about the selected antagonist(s) (Kunoh 2002). _Trichoderma,
Bacillus_ and _Pseudomonas spp_. have often been cited as having potential to controlling
soil borne plant diseases and to increase crop yields (Cook and Baker 1983; Papavizas
1985; Backman et al. 1994; Chen et al. 1999)._ Mycorrhizal_ fungi, arguably the 
most widely studied and understood of all microbial species, act symbiotically with
plants,  positively affecting nutrient uptake, plant growth, disease control, water
holding capacity, and the production of glomalin; the earths storehouse of soil 
carbon.

_Glomus mosseae_ is reported to be the predominant _Mycorrhizal_ species in apple
orchards in New Zealand. Enhanced spore germination rate and development of _Glomus
mosseae _has been seen in the presence of _Trichoderma spp_. Calvet et al (1992)

Further Catska (1994) reported suppression of phytotoxic micromyceles and resultant
replant symptoms by _Mycorhizal _fungi.

Having an understanding of these fundamental soil properties, the addition of beneficial
microorganisms work with you, improving crop profitability, whilst enhancing soils
for future generations through the substances they secrete.

Roots Shoots & Fruits Ltd.