- Healthy soil is productive soil
- Soil biology relates to the organisms within soil that carry out a wide range of processes that are important for soil health and fertility
- The more organic matter retained, the greater the amount of food for biological activity in the soil
- Undertaking particular management actions at specific sites will help maximise the benefits of soil organic matter
- Soil biology contributes directly to more profitable and sustainable farming
- Soil biology remains poorly understood in the context of agricultural farming systems
|Understanding the question
|Why is it important to me as a farmer?
- Active soil biology is essential to improve and sustain agricultural production - a healthy soil is one that is full of life where organic material and nutrients are recycled
- In dryland environments, biological sources within the soil can provide up to 80% of total nitrogen requirement of crops when conditions are optimised
- Soil organic matter has declined significantly in many soils since they were cultivated for cropping - consequently these soils may be less able to supply nutrients to meet plant demand through microbial activity
- High levels of organic carbon helps to maintain agricultural production through its positive role in maintaining soil health, raising fertility, reducing erosion and encouraging soil biota
|Background on soil biology
- Soil Biology relates to the organisms within soil that carry out a wide range of processes
that are important for soil health and fertility
- These organisms decompose and recycle soil organic matter (SOM), improve nutrient
availability and soil structure, transmit or prevent diseases, and degrade pollutants
- The total number of organisms, species diversity and their activity will fluctuate with
changes in the soil environment
- These living organisms can be classified by size into:
- macrofauna (> 10 mm) such as earthworms, termites and other large insects
- mesofauna (range in size from 200 um to 10 mm) such as mites and collembola
- microfauna (20 - 200 um) such as protozoa and nematodes
- microflora such as fungi and bacteria
- Collectively, these groups make up the soil biota and the total mass of organisms
comprises the soil biomass
- Bacteria and fungi are the most numerous, being several
million organisms (producing up to 1 km of fungal hyphae) in each gram of soil
- 70 - 80% of soil biota exists in the top 10cm of soil
- In 1 gram of soil, there is potentially over100,000 different species and greater than10
million different individuals
- Different types of soil biology have different roles and functions:
- Ecosystem engineers such as ants and earthworms that primarily alter the
physical structure of soil but also have an influence on the overall rates of nutrient
cycling and energy flows
Figure 1 – Ant and earthworm – Ecosystem engineers. - Source: DEPI Victoria - Understanding Soil Biology Module.
- Litter transformers that fragment plant litter & improve availability to microbes
Figure 2 – Springtail – Litter transfomer. - Source: DEPI Victoria - Understanding Soil Biology Module.
- Micro-food webs where bacteria and fungi:
- decompose plant litter through enzyme action
- provide a food source for predatory protozoa, nematodes & arthropods
Figure 3 – Micro food web biota. - Source: DEPI Victoria - Understanding Soil Biology Module.
Importance of soil biology:
- For farmers there are 3 components to consider in terms of why soil biology is
- the natural processes themselves (engineers, litter transformers & microfood
- the impact of management on these processes
- the combined effect on plant performance
- The processes that are mediated by these soil biota impact on plant (and animal)
production systems by modifying the soil physical, chemical and biological
environment within which plants grow and persist
- Agricultural management regimes modify biological processes that may benefit
plants in the short-term but cause damage to the soil/plant ecosystem in the
- Soil biology provides both direct and indirect benefits to the environment in that
- Decompose plant residues
- Regulate plant nutrient supply and loss (e.g. N, P, K, Fe)
- Improve soil structure (aggregate stability)
- Degrade pesticides and herbicides
- Regulate water quality (e.g. filters nutrients)
- Capture and release greenhouse gases (carbon dioxide, methane,
- Soil biology also plays a key role in the carbon cycle where soil biota assimilate
carbon and act as a large carbon sink as well as providing a substrate carbon
source upon their death for other soil biota
Key regulators of soil biology
- There are 2 types of soil regulators:
- Primary regulator examples are soil water, temperature and soil type and these
regulators are highly interrelated. We as humans have little direct control over
- Secondary regulators are directly influenced by human interactions with the soil
resource – hence they are known as anthropogenic regulators. Examples of such
regulators may include:
- SOM quality and quantity (which might be determined by the crop type
and sequence of cropping)
- Soil disturbance (which would be directly affected by tillage)
- Inputs to the soil (for example fertilisers, animal manure & urine,
herbicides, lime and inoculants
Distribution of soil biology:
- Soil Biology is not evenly distributed in soil
- It usually occurs in ‘hot-spots’ associated with soil organic matter, which are:
- Decomposing residue - which is an obvious site for both physical and
enzymatic attack by a range of soil biota
- Rhizosphere - which is the soil zone that surrounds and is influenced by
the roots of plants and is likely to have a suite of both positive (e.g.
nitrogen-fixing bacteria and fungi) and negative biota (e.g. fungal and
bacterial pathogens) in close association
Figure 4 - Rhizobium nodules on a legume plant help fix N. - Source: QDPI.
- Macro aggregates - relatively large particles of soil
Soil biology in the Corangamite region:
- Little is known about soil biota conditions in the Corangamite region
- DEPI in collaboration with WestVic Dairy is investigating the impact of different fertility levels on dairy pastures/li>
- It is most likely that high biota numbers will be found in soils that are well structured, have high organic carbon levels and a near neutral pH
|Managing the soil biology
|What is the best practice?
The most important influences on soil biology in terms of management (secondary regulators) are listed below in order of importance:
- Energy supply (which is essentially the carbon in the soil habitat), in the form of plant residues and animal manures. The energy or carbon essentially drives the entire soil ecosystem and its important to help sustain biological functions for longer periods within the season in order to increase levels of microbial populations and associated benefits
- Habitat is also important. It should be steady in terms of water supply, air supply and temperature and should have an absence of toxicities, such as salt, heavy metals etc
- Finally diversity of crops and plant species is important to capture the synergies between species and avoid build-up of pathogens
Soil biological processes develop slowly and will require time to build up in different soils and environments. Growth and survival of soil organisms is dependant on varying soil conditions and land management practices, but are best managed by:
- Increasing organic matter inputs, which will result in a larger, more diverse microbial population and decrease the risk of disease expression
- Maintain rotational diversity by including legume and brassica crops as a disease break and to increase the diversity of organic residues
- Reduce tillage to maintain soil condition and organic matter status to support a greater diversity of organisms
- Manage soil to support naturally occurring living organisms to control the numbers and activity of pathogenic organisms (maintain soil structure, aerobic conditions)
- Manage soil cover to increase the number of days a soil remains moist (‘biologically active’ days) and to control erosion and buffer from extreme temperature
- Fertiliser inputs should be calculated to complement nitrogen cycling from organic matter and enhance the P sourcing activities of AM fungi
- Ensure appropriate use of pesticides only when they are really needed, and avoid repeat applications of the same types of chemicals
|How can you achieve this?
Managing soils to improve biology
- Manage soil pH
- Beneficial soil biology requires soil pHs to be near neutral. If soils are strongly acidic, apply lime to correct pH
- Is the first and easiest way to enhance soil biological populations if your soil is strongly acidic (pHw<5.5)
- Use organic fertilisers
- Consider substituting some of your inorganic fertilisers with organic fertilisers such as composts and manures
- The additional carbon inputs will be beneficial for biological activity
- Increasing soil organic carbon levels through the modification of management practices and complementing inorganic fertilisers with organic fertilisers will contribute to a more sustainable production system in the longer-term
- No-till, stubble retention & direct drill:
- Less disturbance of habitat, water and food supply as well as increased
- Soils are wetter and cooler under no-tillage than when cultivated and
more residues and manures are concentrated on the surface and in the
top layer of the soil
- Occasional tillage may provide short-term benefits with weed control,
pathogen reduction etc
- However, accelerated decomposition from tillage may lead to loss of C
from residues and SOM, in particular following droughts and
synchronization between N mineralization and plant needs may be
- No-tillage tends to favour fungi and their predators over bacteria.
- Retention of stubble increases the food supply (C) of the soil biology
Figure 5 - No till practices. - Source: DPI Understanding Soil Biology Module. DEPI Victoria.
- Crop rotations:
- For the management of pests & disease, soil nutrients and weeds and
for a variety of OM inputs
- Replacing monocultures (usually wheat) with rotations based on crop
legumes, oilseeds and pastures can increase the size and diversity of
the soil biology and facilitate management of soil-borne diseases as
well as improving soil nutrient supply
Figure 6 – Crop Rotations. - Source: DEPI Understanding Soil Biology Module.
- Minimise use of pesticides: (insecticides, fungicides and herbicides)
- Most appear to have no long-term consequences for soil biology but their
use should be minimised
- Insecticides and fungicides generally have a greater negative effect than
- Fungicides will affect beneficial soil fungi and other organisms
- Strategic spraying to reduce application
- Avoid repeated use of same chemical
- Avoid copper based products
- Avoid methyl bromide which will either totally or partially sterilise the soil
- Maintain and conserve ground cover
- To maximise wind erosion control, stubble should cover a minimum of 70% of the soil surface, preferably be standing (anchored by roots) and be a minimum height of 10 cm
- Adopt appropriate grazing management strategies
- that minimise the impact of grazing on soil structure and maximise organic matter returns
Figure 7 – Use of chemicals. - Source: DEPI Understanding Soil Biology Module.
|Other related questions in the Brown Book
Brown Book content has been based on published information listed in the Resources and References sections below
- Johnston, T Understanding Soil Biology. DPI Healthy Soils Modules. DPI Victoria.
- Clarkson T, Department of Primary Industries on behalf of the Corangamite Catchment
Management Authority (2007) Corangamite Soil Health Strategy 2007. Corangamite
Catchment Management Authority, Colac, Victoria.
- Soil Biology. Victorian Resources Online – Department of Primary Industries, Victoria.
- Why Soil Organic Matter matters. CSIRO.
- How Much Carbon can Soil Store. Soilquality.org.au.
- Using biological activity to improve soil. Section D7 - SOILpak - southern dryland farmers. Department of Primary Industries, NSW.
- Soil carbon. Department of Primary Industries, NSW.
- Woady Yaloak Catchment GroupEvaluating alternative fertilisers and biological
products for pastures and crops. Result of the 2009 and 2010 seasons.
- Soil biology in agriculture. (2004 Workshop Proceedings).
- Kirkegaard J, Kirkby C, Gupta V. - Management practices for building soil carbon. CSIRO.
- Soil biological attributes - Best practice principles for managing beneficial soil organisms SoilHealthKnowledge.com.au.