The Queensland Gardening Pages

Information & resources about plants & gardens for Brisbane & Qld

Soils

and soil amendments

This page is intended to provide information primarily about pH, CEC, wettability and salinity of soils, or their physical composition and structure. The topics of soil fertility, soil structure and soil chemistry can't be separated completely because many fertilisers and mulches contribute both plant nutrients and add organic matter. On the other hand, some materials added to correct pH problems can also contribute plant nurients. Furthermore, issues like pH and aeration can have an effect on the availablility and uptake of plant nutrients present in the soil.

News

Bacteria build soil

Research suggests that a significant proportion of soil organic matter may not derive from plant material directly, but from the remains of the soil microflora that feed on it. Bacterial cell wall fragments, resistant to further decay, thus contribute to the long-term soil carbon store. Bacterial products also coat mineral soil particles with an organic film, on which such particles can be accumulated. Source: Fertile soil doesn't fall from the sky. The contribution of bacterial remnants to soil fertility has been underestimated until now (December 2012)

Older news items at the bottom of the page.

Where to buy soils, soil conditioners and other soil ammendments

For the home gardener requiring bulk quanities of soil, sand, gravel etc, call a local Landscape Supply Yard.

If you only need a small amount, these products may also be available in bags from garden centres and the garden departments of variety stores and hardware chains.

Some specialised products (including organic products) may also be available from specialised nurseries and online suppliers.

Cation exchange capacity

Cation exchange capacity (CEC) is a property of soils and growing mixes that is rarely discussed in mainstream gardening literature. However, it plays a very important role in nutrient-retention by soils which subsequently affects fertiliser efficiency and plant growth.

Many important plant nutrients, when added as fertilsers or released from breakdown of insoluble minerals and decomposition of organic matter, exist dissolved in in soil moisture (the soil solution) as negatively-charged ions (cations). Examples are potassium, magnesium, calcium and ammonium nitrogen.

In dissolved form, there's a limit to the amount of nurients that can be stored in the soil and they are vulnerable to leaching.

Fortunately, certain types of positively-charged substances in soil have the ability to cling onto cations, while keeping them relatively available for uptake by plant roots. Cations can re-enter the soil soilution by swapping places with other cations in solution.

The "cation exchange capacity" of a given soil will depend on the amount and type of such substancess it contains. Clays generally have a high CEC (although it it varies with the type of clay). Sand has none. Humus also has a high CEC, and is one of the ways in which organic matter improves soil.

Note that sodium is also a cation. Swamping the clay particles with positve charge affects soil structure and is one of the problems associated with salinisation of soils. More about this at a later date.

Cation exchange capacity: Bibliography and further reading:

The above is a very simplistic introduction to CEC for those unfamiliar with the term. If you'd like to investigate this topic further, here are a few links to get you started:

Cation exchange capacity NSW Department of Primary Industries

Fundamentals of Soil Cation Exchange Capacity (CEC) Purdue University

Cation Exchange University of Florida

Cation Exchange Capacity (CEC) terraGIS (UNSW)

Soil Properties: Exchangeable Cations terraGIS (UNSW)

Cation Exchange University of Florida

Cation Exchange North Carolina State University

Fundamentals of Soil Cation Exchange Capacity (CEC) Purdue University

What is Humus?

Most gardeners have probably heard of humus, but what is it really?

"Soil organic matter" is a broad term encompassing plant roots, soil organisms, root exudates, charcoal and organic matter in various states of decay. "Humus" is the dark-coloured end product. It's composed of complex organic molecules that are relatively resistant to microbial decomposition and under suitable conditions can persist in the soil for a long time.

Benefits of humus include cation exchange capacity (see above), pH buffering, water retention and improved soil structure. For these reasons, gardeners and farmers strive to build the humus content of their soils.

Besides soils and composts, "humic substances" can be found in coal, peat, streams, lakes, organic sediments and some seaweeds. Extracts of coal and seaweed are often used to produce commercial soil improvers. Some vendors claim a variety of plant growth-enhancing properties for certain products.

"Humic acid" and "fulvic acid" and "humin" are components distinguished by their chemical behavior. Humic acid can be precipitated with acid from a sodium hydroxide solution. The resultant solid is called "humate", although this term is sometimes applied to humic subtances more generally. This is a complicated subject and loose usage of these terms in horticultural literature makes it even more confusing.

Humus: Bibliography and further reading:

International Humic Substances Society

Soil carbon sequestration - myths and mysteries Department of Primary Industries and Fisheries, Queensland (PDF)

Humate and Humic Acid

Factors which influence soil carbon levels CSIRO

Overview of humate production in North America New Mexico Bureau of Geology & Mineral Resources

More Information Resources

Queensland Soil Types

Soils in Queenlsand Department of Environment and Resource Management

Types of soil and plants Overview of the soils of Brisbane. Brisbane City Council

Geology - South-East Brisbane by Villanova College (Coorparoo)

Soils of Ipswich Field Guide Ipswich City Council (PDF)

Soil Classification & Regional Patterns with special references to Soils of the Bundaberg area. Part of the 'Physical Geography of Australia'course materials from Central Queensland University

2003 Workshop on Soils in Rural Queensland 29 - 30 July 2003 at Toowoomba Department of Main Roads, Queensland

Cropping soils of central Queensland Dept Primary Industries & Fisheries, Queensland

Look for regional gardening and environmental groups (who might be able to supply information on local soils) on the Regional pages.

General Information

Note that commercial products, regulations, plants and soil types vary from place to place, so some information in links may not apply where you live.

The Australian Soil Classification Online guide. CSIRO

Australian Soil Resource Information System CSIRO

Australian Society of Soil Science

Understand your soil type. (a general overview for the beginner) Queensland Dept Environment & Resource Management (PDF)

Understanding soils A number of factsheets can be downloaded from this page. Queensland Dept Environment & Resource Management

Soil health for vegetable production in Australia This soil science manual, which should be of interest to serious gardeners and students of horticulture as well as farmers, can be downloaded in PDF formfrom this page. Department of Employment, Economic Development and Innovation

What is Soil? Basic overview. Department of Primary Industries Victoria

Soils (General) State of Victoria, Department of Primary Industries, Victoria

Better Soils Agricultural Bureau of South Australia

Soil biology basics factsheets on a variety of topics available from this page. NSW department of Primary Industries

Soil Science Education Homepage National Aeronautics and Space Administration (NASA) USA

SERG Soil Ecology and Restoration Group, San Diego State University, USA

Check your soil structure Department of Primary Industries, Victoria

Soil Texture University of Florida

Use of Soil Amendments in Landscape Plantings University of Hawaii at Manoa (PDF)

Alternative Soil Amendments Appropriate Technology Transfer for Rural Areas

Improving Garden Soil Fertility Oklahoma Cooperative Extension

Soil Science Society of America

British Society of Soil Science

Water penetration and retention

Does gypsum improve clay soils?

There's a widespread misconception, even amongst horticulture professionals, that gypsum can improve the structure of every clay soil. Check out the following links:

Does my soil need gypsum? Department of Primary Industries, New South Wales

Emerson Aggregate Test NSW Department of Natural Resources (PDF)

Identifying gypsum-responsive soils

How to manage soil for citrus (see notes on soil testing and gypsum use) NSW Department of Primary Industries

Understand the behaviour of your soil Natural Gypsum Miners Association, Australia

Gypsum New Zealand

What About Gypsum? Colorado State University

Clay garden soils require special care University of California, Davis

How to improve clay soil Extension Service Garden Hints, Oregon State University

pH (Acididity or Alkalinity)

These links have been moved to a new page: Soil pH

Organic Matter, Carbon

See also articles on Humus and Cation Exchange Capacity above

Soil carbon: the basics CSIRO

Soil Organic Matter DPIW Tasmania

Composts in the Landscape: Effects on Soil pH and Plant Growth Ohio State University USA

The Myth of Soil Amendments, Part III Can you add too much organic matter to a soil? Washington State University (PDF)

Overview of Cover Crops and Green Manures Appropriate Technology Transfer for Rural Areas, USA

Using Manures in Gardens Yard and Garden News, University of Minnesota

Manures for Organic Crop Production Appropriate Technology Transfer for Rural Areas, USA

What is mushroom compost? Extension Service Garden Hints, Oregon State University

Mushroom compost - use carefully Extension Service Garden Hints, Oregon State University

Mushroom compost as a soil amendment for vegetable gardens Reproduction of a 1989 article, Proceedings of the Florida State Horticultural Society (PDF)

The International Biochar Initiative (IBI)

How earthworms can help your soil NSW Department of Primary Industries

Australian and New Zealand Biochar Researchers Network

Should we use biochars in our gardens? Post at The Garden Professors blog, Washington State University

Plant nutrients

Soil factors such as pH and cation exchange capacity will affect the behaviour of nutrients with the soil and availabitlity to plants. The nutrients themselves are covered in more detail on the Plant nutrition and nutrient deficiencies page.

Salinity

Using conductivity meters in agriculture Dept of Primary Industries and Fisheries, Queensland

Minimising salt damage in home gardens Department of Agriculture Western Australia (PDF)

Soils and Fertilizers for Master Gardeners: Tackling Soil Salinity Problems in the Home Landscape University of Florida

Soil Salinity, Salt Tolerance, and Growth Potential of Horticultural and Landscape Plants University of Wyoming

Diagnosing Saline and Sodic Soil Problems Colorado State University Extension

Soil testing

How to Sample Soils Used for Flower, Fruit, Grape and Vegetable Production Department of Primary Industries, Victoria

Soil Testing and Sample Collection Missouri Botanical Garden

Putting Your Soil to the Test Montgomery County, Maryland

Using conductivity meters in agriculture Dept of Primary Industries and Fisheries, Queensland

Soil Science Laboratory Manual University of Virginia

Other

Soil compaction Dept Primary Industries & Fisheries, Queensland

The Myth of Vibrating Vehicles Does vibration from traffic causes soil compaction nearby? Washington State University (PDF)

Soil Compaction in the Urban Landscape University ofFlorida

The Myth of Soil Amendments Part II Will adding sand improve the texture of a clay soil? Washington State University (PDF)

www.perlite.info information about perlite

australianperlite.com.au

vermiculite.org

Incorporating Zeolite into Soilless Container Media Reduces Nutrient Leaching in Ornamental Plant Production (scroll down the page to view the abstract of this research) University of Florida

Microbial amendments and microbe-friendly additives for the soil Dept Primary Industries & Fisheries, Queensland

Mycorrhizal Information Exchange

Lead Contamination in the Garden Ohio State University

Plants suitable for heavy clay soils Department of Natural Resources and Mines, Queensland (PDF)

Plants suitable for sandstone or shale areas Department of Natural Resources and Mines, Queensland (PDF)

Plants suitable for seaside areas Department of Natural Resources and Mines, Queensland (PDF)

Manufacturers and distributors of soil conditioners and amendments available in Qld are invited to advertise on this page. For example: composts including treated wastes, wetting agents, pH adjustment, water storage additives (granules, gels), additives for drainage and porosity, flocculation agents. More information about advertising.

More about plant nutrition and fertilisers here: Plant nutrition

More about mulches and mulching practice here: Mulches

More about growing media for containers here: Potting Mixes

If you're looking for a place to buy soil in Qld, go to: Landscape Supply Yards

Older News

Tree-soil-microbe interaction creates limestone

Scientists have discovered a bacterium that can incorporate carbon dioxide into limestone, with the the help of a tropical tree and a fungus. Under certain conditions, the tree combines soil calcium with atmospheric CO2 and the bacterium creates the conditions under which it can be converted into calcium carbonate, depositing limestone around the tree's roots. This is a way of both improving the soil for agriculture or reforestation as well as locking away carbon in the soil and is already being trialled in several tropical countries. Source: Bugs in key role of CO2 storage method (June 2012)

Soil microbe erosion
The damage caused by wind erosion extends beyond the loss of soil particles, but the microorganisms that play such an important part in soil building and nutrient recycling. DNA sequencing employed in a recent American study (Agricultural bacteria: Blowing in the wind) shows that different groups responsible for various soil processes tends to be associated with different fractions (e.g. course particles versus fine dust).. these may be lost or retained depending on the nature of the erosion. The DNA technique, besides helping identify what may be lost during a particular erosion event, could also provide early confirmation of soil improvement from better management. (May 2012)

Poorly made biochar not beneficial
Biochar is becoming so popular worldwide that many people are now trying to make their own at home. A study at Rice University, USA, has found that the expected beneficial effects depends on how the charcoal is produced. The study found that unless heated to at least 450°C it could repel water and be less stable as a long-term carbon store, whether made from tree leaves, corn stalks or wood chips. Source: Cooking better biochar: Study improves recipe for soil additive (March 2012)

Biochar and earthworms get along
Reseachers have found that lack of moisture when dry biochar was incorporated into soil caused unwanted effects on earthworms. This suggests that when biochar is used in the field, pre-wetting or immediate irrigation after incorporation may be may be necessary. Fortunately, biochar was found to have no effect on the reproduction or immune systems of earthworms studied. Source: Study Finds Greenhouse Gas Reduction Strategy May Be Safe for Soil Animals (June 2011).

Biochar could help conserve water
Research at Tamworth Agricultural Institute is investigating the use of biochar on pastures. Results so far indicate potential for improving water use efficiency. Source (NSW Department of Primary Industries): Australian-first research looks at impact of biochar on water efficiency (April 2011)