Aug 082013
 

Photo © Bulleen Art & Garden

For over 400 million years there has been a mutually beneficial relationship between the root tips of plants and mycelium (fungus).

The term ‘VAM’ – Vesicular Arbuscular Mycorrhiza – is used to describe one such type of this beneficial relationship between the root tips and the fungi.

The mycelium enters the root tip and together they form a site where nutrients and carbon can transfer. This assists the plant in absorbing the essential nutrients for growth. VAM is an additional way the plant has of absorbing nutrients, and makes it possible for plants to grow in conditions that are suboptimal (nutrient deficient) – such as many Australian soils. Without VAM, the direct uptake of nutrients by plants via their root systems can result in a nutrient deficiency in the soil immediately adjacent to the root zone. Subsequent absorption of nutrients is then limited by the rate at which roots can grow into new soil and by the rate at which nutrients move through the soil. With VAM, the extensive network of mycelium grows past the depletion zones and allows nutrients to be actively transported into the root system. This method is a much more efficient way of maintaining contact with nutrients than the plant continually extending its root system into fresh soil.

Benefits of VAM

The benefits of VAM are many and well documented. VAM inoculants have been available commercially in agriculture (and hydroponics) for some time and are only now being packaged in sufficiently small quantities to be available for use in the home garden (1kg and 150g bags instead of large drums).

There are many benefits of adding VAM inoculants to the home garden and they include:

  • Increased establishment and survival of seedlings (fungi enter the emerging roots and rapidly establish the beneficial relationship aiding survival and successful establishment)
  • Higher growth rate and greater plant size
  • More and better quality fruit and leaves with a higher nutritional value.
  • Increased tolerance to drought
  • Increased tolerance to pests and diseases

Due to the symbiotic nature of the relationship between the fungi and the plant root tips, if you leave an area fallow (no plants in it) the fungi will die. Consequently, in your vegie garden, if you don’t want to grow a winter crop after your summer crop, rather than leave the patch fallow we recommend you sow a green manure crop.

There are many other benefits of VAM, here are some links if you would like to investigate further. Click here for a good over-view of mycorrhizza. For an extensive discussion on VAM, its modes of action and application in agriculture / horticulture, click here and follow the links.

Organic Matter

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Aug 082013
 

Organic matter is anything that contains carbon compounds that were formed by living organisms. It consists of dead and decaying forms (mainly plants and manures), living plants (mostly roots) and living micro-organisms and soil animals

Why do we care?
Because nutrients taken up by plants in the natural environment (this excludes commercial agriculture) are derived largely from the decomposition process of soil organic matter It is easy (and cheap!) to make your own compost. If using your own chicken or farm manures, it is a good idea to run it through your compost system where the heat of the composting process will destroy most weed seeds. Fresh chicken manure is too ‘hot’ to use directly in the soil and should always be composted before use.

Confusion?
Humus, compost and organic matter are often incorrectly used interchangeably. Humus and compost are different, but both are components of organic matter.

Improving soils

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Aug 082013
 

It can be very tempting to look at the soil you have and think it is better to replace it with soil you can buy in. It looks all fresh and new, problem free and feels like a clean slate. Ignoring the environmental aspects of digging up soil, dumping it, creating new soil, relocating it etc, there is a good chance you are better off improving the soil you have rather than replacing it. Better off in that you will have both a superior soil and more money in your pocket.

Many soils you buy are constructed soils, so they are relatively uniform from one batch to the next. These soils can have no, or minimal, clay component, which is a problem in the medium to long term. Often deplored by gardeners, clay has many highly superior qualities and plays a vital role in good soil. You will end up with a beautiful rich dark fruitcake of a soil if you improve your existing clay based soil.

When discussing soil improvement, the first step is appreciating the benefits and essential nature of organic matter. No matter which literature source you access, whether peer reviewed journals, university fact sheets or garden blogs, it is impossible to escape the vital role organic matter plays in the soil.

For Australian soils adding organic matter is almost always extremely beneficial. Add in both compost and manures, spread out over the top and then dig in to around a spade depth. Do not over work the soil and try to work when soil is damp – not dry and not wet. The addition of organic matter allows the build up of worms, soil arthropods and soil micro-organisms; these decompose the organic material and in the process provide nutrients for plant uptake.

Very occasionally (almost never) an enthusiast will add in far too much organic matter resulting in salt build up, large nitrogen release, excessive phosphorus and an imbalance of other minerals. This is rarely a problem in Australia.

Keeping the soil moist – to a level of a wrung out sponge – is important in keeping the soil micro-organisms alive, and these are vital for good plant health. Mulch is very beneficial in improving soil moisture and adding organic material to the soil. As the soil micro-organisms break organic matter down and drag it into the soil, it needs to be replaced periodically. If the organic matter is not replaced, the soil micro-organisms will die and soil fertility will fall.

If you have resorted to importing soil it is important to avoid ‘textural interfaces’. This is where you have one type of soil laid directly over another type of soil; the resulting difference in pore spaces interferes with soil water movement and root development. Make a transition layer between the soils, mixing the fill (imported soil) with the soil underneath.

Humus

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Aug 082013
 

Humus is organic matter that is decomposed to the point where it resists further decomposition and is stable and accumulating in the soil. It is mostly extremely stable carbon compounds with no phosphorus or nitrogen. The stable form makes it difficult to break down by microorganisms.

Why do we care?

Nitrates (NO3-) stay in solution between the soil particles and are readily leached from the soil. Humus has a positive charge and aids in holding the negatively charged nitrates in the soil profile, making them available for plants to take up.

Humus has extremely high absorption abilities. It can hold and release water and nutrients as needed. It also improves the physical structure of soil so that it is crumbly and aerated.

Confusion?

‘Humus’ is often incorrectly used instead of the term ‘compost’. Compost is able to be broken down in the soil releasing nutrients for plants, unlike humus.

Aug 082013
 

Photo © Bulleen Art & Garden

Soils in established gardens can become very undernourished over time unless careful maintenance is used. The loss of organic matter by the continual tidying and removal of leaves and prunings leaves the soil hungry and depleted with minimal worm and micro-organism activity. When major soil amendment is not possible because of existing roots of trees, shrubs, perennials and lawns it is still possibly to make significant improvements in the soil.

With the exception of fungi, nearly all soil micro-organisms and worms need a moist environment to operate successfully in. If soils have dried out and become hydrophobic then you will need to treat that first. Keep soils moist and spread manures over the top – no more than 5cm thick, and allow the soil fauna to drag the manures into the soil. Once manure has disappeared, can repeat manure application or use a pea or lucerne straw mulch. This will add organic material as well as keeping soil moisture at good levels for the worms and soil micro-organisms to operate effectively. If available, spreading liquid worm waste from worm farms is greatly beneficial.

For a more concentrated fertilizer ‘hit’, use the pelleted form of manure based fertiliser and sprinkle over the soil before spreading mulch. It can also be used when mulch is topped up. Controlled release fertilizers can also be used in conjunction with mulch, these will aid plant growth, but do little to improve your soil directly. However, increased root growth assists many soil micro-organisms as they live in the rhizosphere (area immediately adjacent to and on the roots).

Minimise soil compaction using organic mulch and managing foot traffic. Compacted soil loses the essential pore space for gas exchanges and for water to move through. Soil compaction is much more rapidly done and serious when the soil is wet. Avoid walking on wet soils where possible and use thick mulch on paths to reduce impact of foot traffic.

A commercial aerator (either a corer or a spiked roller), can be used to aerate soils without causing too much damage to plant roots. After aeration, spread manures or compost over and rake through.

Aug 082013
 


There are a couple of significantly good things about clay soils: the tiny particles which are the building blocks of the clay soil are extremely good at holding onto both water particles and onto nutrients (high cation exchange capacity). This greatly increases the water holding capacity of your soil as well as the ability of the soil to retain nutrients, so they don’t just wash through the soil profile and become lost, leaving the soil hungry again. Soils with no clay (sandy or shale soils) can be very difficult to manage in the long term, becoming easily hydrophobic and struggling to retain moisture and nutrients.

When confronted with a hard clay soil it is tempting to just throw your hands up in despair and import soil. However, it is in your own interests to try and improve what you have, as imported soil often has no clay component at all and requires lots of attention over the years also to improve it in the long run. Clay soils obviously have their problems, but they can be addressed.

The lack of large pore spaces in clay soil restricts water and air movement, resulting in easily waterlogged and anaerobic soils. The only practical way to improve this is the routine addition of plenty of organic matter (can be compost or manure) and fostering the activity of earthworms and soil micro-organisms. These decompose the organic matter and the tiny soil particles are bound with the organic material into clumps resulting in increased pore spaces. Spread organic material 3-10cm thick, and dig in to a depth of around 20cm. Do not over work the soil. Green manure crops are excellent – grown, then turned into the soil when 1/3 to ½ grown, green and lush. Dig in once a year in spring or autumn.

A single large application will not do the trick. It is essential that this is repeated over a number of years. After 2-3 years improvements will be seen and the rate of improvement will rapidly increase as the organic matter increases and earthworms and micro-organisms become more active. Eventually you will get that rich dark fruitcake soil you are after.

If your clay soil is a sodic soil (common around the Bulleen area) then adding gypsum in conjunction with the organic matter will help.

Avoid compacting clay soils – especially when wet, watch foot traffic, use heavy mulch on paths to avoid compaction.

Avoid excessive cultivation, use just enough to incorporate organic materials and fertilizer. Cultivate when moist but not wet (and not dry).

Plums

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Aug 082013
 

Bursting with flavour, plums are a summer delight. These graceful, deciduous trees with thick, coarsely-toothed leaves are an asset to any garden and were once found in most suburban back yards. Plums together with Figs are probably the easiest of the fruit trees to grow. The don’t get peach leaf curl, cherry slug, leaf miner, gall wasp, codling moth or oriental moth. Gummosis is rarely a problem. Really, all they need is sufficient sun, food and water.

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Aug 082013
 

Photo © Bulleen Art & Garden
We tend to forget that our soil has a significant amount of animal, fungal and single celled life in it… but it is this very life that is essential in making available much of the nutrients that plants use. From the microscopic soil bacteria through to the readily visible earthworms and arthropods, these living components of the soil are the often overlooked workhorse in turning organic matter into food for plants.


Only a small percentage of the total soil, yet it is this most fragile component that beavers away industriously, doing its own thing and simultaneously making the soil infinitely better for plant growth. Below is a discussion on the some of the various components of the living soil network. It is just a tiny snapshot of the extraordinary life that exists in our soil, why we need it, and how to ensure your soil is teeming with life!

Photo © Bulleen Art & Garden
The Living Soil – Bacteria
There are three major groups of beneficial soil bacteria; Nitrifying bacteria, nitrogen fixing bacteria and Actinomycetes.

Nitrifying Bacteria
These highly beneficial bacteria convert Ammonium (NH4) to Nitrite (NO2) to Nitrate (NO3) which is the preferred for of Nitrogen for many grasses and crops.

Nitrogen Fixing Bacteria
These have a symbiotic relationship with the roots of many legumes and of some trees. The bacteria infect a root hair creating a nodule. The plant supplies carbon compounds to the bacteria which in turn converts N2 from the air into a form the plant can use.

Actinomycetes
These grow hyphae like fungi and are responsible for the typical earthy smell of freshly turned healthy soil. They decompose a wide array of material but are especially important in degrading the hard to decompose organic matter to forms other soil micro-organisms can use. They are mostly active in higher pH soil.

Encouraging soil bacteria
These are mostly concentrated in the rhizosphere (narrow region adjacent to the roots), so it is important to keep living plants in the soil. Instead of leaving your vegie bed fallow for a season, plant a green manure crop instead.

Bacteria live in water in the rhizosphere and will not survive without water, keeping the soil moist is important, using a mulch will help lower evaporation and assist in keeping an even level of soil moisture.

Photo © Bulleen Art & Garden

The Living Soil – Protozoa

These single celled ‘animals’ feed on bacteria, organic matter and other protozoa. As they feed on bacteria they release ammonia (NH4). They help regulate bacteria numbers and aid in suppressing disease by competing with and feeding on pathogens, they also mineralize nutrients making them available for use by plants and other soil micro-organisms. Protozoa provide a major food source for soil micro-organisms.

Encouraging protozoa

These are mostly concentrated in the rhizosphere (narrow region adjacent to the roots), so it is important to keep living plants in the soil. Instead of leaving your vegie bed fallow for a season, plant a green manure crop instead.

Protozoa will not survive drought conditions, as they need water to move in and bacteria to eat (also water dependent). Thus keeping soil moist is very important; using a mulch will help lower evaporation and aid in maintaining an even level of soil moisture.

Photo © Bulleen Art & Garden

The Living Soil – Nematodes

These non segmented worms compete with protozoa for bacteria, organic matter and other nematodes, and like protozoa as they feed on bacteria they release ammonia (NH4). They help regulate bacteria numbers and aid in suppressing disease by competing with and feeding on pathogens. There are a few species responsible for plant diseases but most play a beneficial role within the living soil network. Nematodes provide an important food source for other soil micro-organisms.

Encouraging nematodes

These are mostly concentrated in the rhizosphere (narrow region adjacent to the roots), so it is important to keep living plants in the soil. Instead of leaving your vegie bed fallow for a season, plant a green manure crop instead.

Nematodes will not survive drought conditions, keeping soil moist is important, using a mulch will help.

The Living Soil – Fungi

Of the many fungi, there are two major beneficial types; Saprophytic fungi and Mycorrhizal fungi.

Saprophytic Fungi
These are important decomposers in the soil converting hard to digest organic matter into forms other soil micro-organisms can use. They also produce the organic acids (humic and fulvic acids) which are used to increase the humic acid rich organic material. The hyphae physically bind the soil particles together and aid good soil structure.

Mycrorrhizal Fungi
These colonise plant roots, taking carbon (in the form of carbohydrates – glucose and sucrose) and in exchange help solubilise Phosphorus and bring in Nitrogen and micronutrients to the plant.


Encouraging Fungi
These fungi will tolerate periods of dryness in soil, but are aerobic, and will die in waterlogged or compacted soils. Using mulch to keep moisture levels up helps. Don’t over work the soil as it breaks up the mycelium. Fungi work best in more acidic conditions, adding lime will reduce fungal populations in favour of bacteria.

The Living Soil – Earthworms

Worms eat by grinding up organic matter and soil micro-organisms. The digestion process changes the material as it passes through the gut, inoculating it with beneficial micro-organisms, concentrating and converting nutrients into a form available to plants. Worm casts release 4 times more phosphorus than does surface soil.

Worm castings are stable aggregated soil clusters, resistant to erosive forces and greatly improving soil structure. The burrowing action of worms drags the organic matter down into the soil as well as creating passages for air, water and plant roots. Worms tend to leave their casts in their worm burrows – further providing a favourable environment for root growth.

Especially beneficial when trying to improve clay soils, the extensive earthworm burrows loosens and aerates the soil allowing water to infiltrate and percolate, and roots to penetrate. In zero-till soils, where worm populations are high, water infiltration can be up to 6 times greater than in cultivated soils. Earthworm tunnels also act, under the influence of rain, irrigation and gravity, as passageways for lime and other material.

The tying together of soil particles with organic matter in the digestion process increases particle size and thus increases pore spaces. The mucus from their skin also aids in the formation of soil aggregates. These actions together are integral to the crumb structure of a good soil.

Encouraging Earthworms

Earthworms breathe through their skin and must be in an environment that is 40% moisture (damp as a wrung out sponge). If the soil dries out and their skin dries out they cannot breath and they die. Mulching helps keep the moisture in the soil.

Keep up the organic matter in/on the soil as a food source: leaf litter, manures, compost, mulch and green manures. They prefer a neutral pH and will not thrive in highly acidic soils. Highly acidifying fertilizers such as ammonium sulphate and some fungicides (Bordeaux and other copper sprays) will reduce earthwork numbers, sometimes severely.

Worms fail to thrive in compacted and waterlogged soils. Avoid traffic in wet conditions.

Worms do not like frost – a good mulch will keep the frost away from the soil and allow worms to survive.

Avoid excessive tillage as it cuts and kills the earthworms.

When conditions are favourable worm numbers can rapidly increase.

The Living Soil – Arthropods

Arthropods have jointed legs and an exoskeleton. Some examples you may know are springtails, beetles, ants, spiders, mites, centipedes and millipedes.

The benefits of Arthropods

They shred plant material, increasing surface area for soil micro-organisms.

They physically move the soil micro-organisms around in the soil and with the plant material.

Soil aggregation is enhanced. In good soils every particle of soil in the upper surface should have gone through the gut of numerous soil fauna. Each time it passes through another arthropod or earthworm it is thoroughly mixed with organic matter and mucus and deposited as a highly concentrated nutrient resource in the form of fecal pellets.

Arthropods stimulate the succession of species – at any one time only a small subset of species are metabolically active, by consuming the dominant species this allows other species to come in which facilitates the progressive breakdown of organic matter.

Predators will eat live prey, some scavenge dead prey. They effectively reduce material to smaller particles and are an important first step in the decomposition process.

Grazing on fungi and bacteria around plant roots stimulates the growth in numbers of their prey. In addition, these microbes are often carried on the exoskeleton of the arthropod and moved through the soil, helping to move them much greater distances than they would otherwise be able to travel.

Potatoes

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Aug 012013
 

Photo from Wiki Commons

Potatoes have been a staple in our diet for hundreds of years. Growing them is easy, so why not start thinking about producing your own home grown potatoes. For those who love their spuds, you’ll love the variety of seed potatoes we now have available at BAAG. They come both packaged and loose and we stock a large range of popular varieties as well as many unusual, designer spuds like Lustre or King Edward.

There’s still plenty of time to plant, so get ready by preparing their beds for planting with loads of well-rotted manures and composts. Potatoes are hungry plants, so you can’t overdo it. Seed potatoes refer to the fact that they are disease-free. They still look like ordinary potatoes, not seeds! You can’t guarantee that the spuds that have started to sprout in your pantry aren’t carrying viruses, so sometimes planting those will lead to disappointment. Read on for more information on planting and available varieties.

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