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

Urban gardeners lack information on soil contamination

One of the potential drawbacks of edible gardening in urban areas is the possibility the soil may have be contaminated from prior industrial uses or fallout from heavy traffic. A study conducted in Baltimore (USA), in which community gardeners were surveyed about their knowledge of these issues, has shown insufficient knowledge and expertise in assessing the risks of a site and how to minimise exposure to contamination that may be present. Source: Urban gardeners may be unaware of how best to manage contaminants in soil (March 2014)

Study reveals unwelcome side effect of biochar

While stimulating marked increases in plant growth associated with brassinosteroids and auxin gene activation, a biochar study also showed that plant defence genes were suppressed by the soil supplement. This could have serious implications for the suitability of biochar for crop enhancement and carbon sequestration. Source: New study finds biochar stimulates more plant growth but less plant defence (March 2014)

Older news at bottom of 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.

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More about improving your soil



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:
Cation exchange capacity NSW Department of Primary Industries
Cation Exchange University of Florida
Cation Exchange University of Florida
Cation Exchange North Carolina State 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:
Soil carbon sequestration - myths and mysteries Department of Primary Industries and Fisheries, Queensland (PDF)
Overview of humate production in North America New Mexico Bureau of Geology & Mineral Resources

More Online Information


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
Cropping soils of central Queensland Dept Primary Industries & Fisheries, Queensland
Soil types EnviroNorth, Tropical Savannas Knowledge in Schools
Laterite Article in The Native Gardener, Newsletter of the Society for Growing Australian Plants Townsville Branch Inc. (PDF)
An introduction to acid sulfate soils NSW Department of Primary Industries
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.
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

Water penetration and retention

Soil water repellency Department of Primary Industries and Fisheries(PDF)
Soil water repellency Dept Primary Industries & Fisheries, Queensland
Soil Resistant to Water? Colorado State University
Using Wetting Agents (Nonionic Surfactants) on Soil N.C. State University, North Carolina
Drought Resistant Soil Appropriate Technology Transfer for Rural Areas, USA
Take a Hard Look at Water-Holding Compounds University of Hawaii at Manoa, USA
Hydrogels: Are They Safe? - January 14, 2009 Discusses polyacrylamide (PAM) hydrogels Arizona Cooperative Extension, Yavapai County
Soil Moisture Monitoring: Low-Cost Tools and Methods National Center for Appropriate Technology (USA)

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)
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
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 Organic Matter DPIW Tasmania
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)
How earthworms can help your soil NSW Department of Primary Industries
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)
Diagnosing Saline and Sodic Soil Problems Colorado State University Extension

Soil testing

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)
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
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
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

Hydroseeding goes organic

Mexican researchers are developing an organic hydroseeding techniques to stabilise sloping roadsides that is actually better than alternatives employing artificial polymers, adhesives and fertilisers. Components of the new technique include mycorrhizae to encourage soil aggregation and an adhesive made from the nopal cactus. Gardens used to reduce landslides (September 2013)

Soil contamination risks in urban gardens

One of the risks of vegetable gardening in urban areas is soil contaminated by toxins. Soil tests may indicate problems, but researchers in Detroit evaluating sampling strategies in a garden plot found that some of the methods failed to detect a lead "hotspot". They suggest that standard sampling procedures be reassessed, and that if possible garden planners check historical records to ascertain what activities the land was previously used for. Source: Detecting Lead Hotspots in Urban Gardens Requires Different Sampling Strategies according to Wayne State research (June 2013)

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)

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)
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