Talk by Dr David “Harry” Harrison, Veterinarian and President of the Rare Fruit Society of South Australia

by admin | October 26, 2020 9:55 pm

Soil Nutrition; Organics v Conventional Farming and Tips on Grafting

Components of soil – Soil has four major components: Air – healthy soil has 25% of its volume as air. It is this space where the roots and living matter (bacteria and fungi) are living. Water – in a fully saturated soil 50% of it might be air spaces filled with water (at field saturation it is 25%).

Minerals – 50% of remaining are typically minerals.

Organic matter and living organisms
Avoid digging organic matter into the soil especially loams and clays (more so than sandy soil). Put organic matter on top and let organisms work it in. The average earthworm has 30,000 different types of good bacteria in its gut. Bad bacteria that pass through the gut of a worm are destroyed. Cover crops and green manures should be chopped and laid on the top of the soil. If you turn a green manure in, do so to less than 10cm. Why leave the cut green manure on the surface of the soil? Rapid decomposition in the soil can use up the available oxygen and nutrients, making them less available to plant roots. If you turn a green manure in, do not plant for a minimum of six weeks, but preferably three months. In a hot, dry climate, cover the cut green manure with a light layer of mulch, enough to stop it from drying out. The depth of aerobic bacteria is another reason for not digging organic matter in. Where are the microbes and the biggest number fungi and algae? Over 80% in the first 7-8cm (3 inches) – then 10-15% in the next 25cm (10 inches) – then things get fairly scarce. It is even less in heavy and compacted soil. Why? Plant feeder roots need oxygen and water. The top section of the soil, the aerobic zone is the healthy part of the soil for plant feeder roots where air can get in and out. Plant roots and organisms produce carbon dioxide and other noxious gasses that need to get out of the soil.Once you go past 15-20% organic content in a soil, you tend to magnify fungal diseases and soil borne pathogens.

Plant/microorganism interactions
Plants give away sugar in fruit, nectar and other means. What is sugar? Carbohydrates (carbon, oxygen and hydrogen). Plants can make this easily via photosynthesis. What good is this to the plant? It attracts animals in to pollinate flowers, distribute seeds and can form a protective mechanism for the seed. They also give away sugar through their roots. Of the total amount of starch produced by a corn plant, an estimated 50% is given away via the roots by being traded off with other organisms. The corn stalk is all sugar, starch and cellulose that has come from sugar. What plants do is look to achieve some balance/control of the rhizosphere. This is the area of soil closest to the roots where the interaction between root secretions and soil biology is most pronounced. By trading sugar, modifying pH and oxygen tension they are trying to influence all the organisms around the root system. The plant roots are helping to keep everything alive by providing habitat and food for bacteria, fungi and other soil organisms. Examples include plants with rhizobia, the nitrogen fixing bacteria inside the root nodules of legumes. The plant provides a capsule that is a low oxygen environment that these bacteria prefer, plus sugar for energy. The rhizobia bacteria provide nitrogen to the plant in return. Try to keep cover crops going as much as possible, because they are adding sugars and the roots are opening the soil up.

Humus is what is left over when all the microbes have a good go at eating everything out of the organic matter that they can eat simply. What is left is very stable organic matter (brown coal is humus worked over for a million years). A lot of material that is sold as compost is not the quality that we need. In a mature compost with high levels of humus the individual components (leaves, sticks etc) that made the compost should not be able to be identified. If you use unfinished compost you are activating all the soil organisms that compete with plant roots (as the microbes break the materials down). Compost is living and should be surface applied, and protected from drying out.

Soil biology
Bacteria, fungi, flagellates, ciliates, beneficial nematodes – there are an estimated 1 billion bacteria in a teaspoon of “healthy” soil; 1-40 miles of miles of fungi per teaspoon in the form of fine filaments; and hundreds of nematodes and arthropods. Where do microbes come from? Biodynamics uses one walnut sized piece of material turned in water and sprayed out over acreage. What is going on here? You have composted some cow manure; created a population of bacteria, fungi and nematodes that are beneficial; then you have multiplied the good organisms aerobically (anerobic are our badies) by stirring a vortex in the water.

Aerated compost tea One of the largest strawberry farms in South Australia has phytophthora in their ground water. They have knocked it out with compost teas that are aerated (plus they add nitrogen, molasses and lots of stirring energy) to create huge numbers of beneficial organisms and them put it through the irrigation system. You could get the same effect by 48 hours of bubbling with a fish tank aerator. Comment: There is a better way of aerating via an air pump that hyperoxygenates the water – this is what the strawberry farm uses, very energy intensive but saves time. Fungi – two classes that are really important. One of the major things about fungi and their mycelium generally, is they can massively increase the root zone that plant roots can get to, by up to ten times. Soil stabilisation in the Sahara with jujubes (Ziziphus jujube) has recognised the role of mycelium in these really harsh conditions. Mycorrhiza work with plants by entering or attaching to, the roots and swapping nutrients. This improves what and where your plants can get their food. Ectomycorrhiza – we see the fruiting bodies of these as toadstools and mushrooms. They do a trade off with plants. They latch on to plant roots. The plant gives the fungi sugars and fungi give the plant phosphate (often locked up) and other minerals. They also help give you more drought resilience, feeding water to the plants. Ectomycorrhizal fungi (ecto – outside/endo – inside) are the important ones for our trees – they are toadstools and mushrooms. But the other really important thing about organic matter is that the humus that is derived from woody matter and trees is the best humus for these ectomycorrhizal fungi so if you want to feed your woody trees and orchards with healthy compost and mulch, it should be wood based. Endomycorrhiza or Arbuscular mycorrhiza (AM) enter the plant roots to trade nutrients. They can produce a substance glomerulin, with glue-like properties which binds soil together and creates structure. They are associated with soft herbaceous plants and some of our trees. The humus that helps the endomicrorhiza in soft herbs and grasslands is best derived from their products – soft green materials. It is pretty obvious that fungi in the soil that has been feeding from the same products in the soil for a million years, is probably accustomed to that food. If you add the breakdown products from something different, it might not be good at all, and not quite as healthy. Make a distinction between what you use as mulch and the products you put in compost that goes to your trees versus your vegetables. Use straw in a vegetable garden and woody material in an orchard for ideal soil health. And it goes even further than that – research into Jarrah dieback (phytophthora) trialled humates derived from jarrah and other woody material. The Jarrah-based humates created the healthiest soil conditions and had the most effect on the dieback. Pyrophylous (fire-loving) fungi

Morels and boletes (Morchella and Boletus species) come after a fire, often as a result of the change in pH because of all the ash. They change the soil for the next species – we are more familiar with this phenomenon of establishment species in plants ecosystems.

What about mushroom compost? Mushrooms from mushroom compost are different to the type of things I am talking about. They are not associated with plant roots. Most mushroom composts have a component of peat and lime. Lime is probably not a problem for you, but I never add lime to compost, worm farms or anything, because I come from an area with incredibly alkaline soils. Wood ash has a pH 9-11 – strongly alkaline. You should always take the precaution of testing the pH of what you use. It is not uncommon for mushroom compost to be 8 or 9. Other than that you are looking at quite a good carbon product when compared with commercial compost, but it has had quite a lot of the protein (nitrogen) taken out of it by the mushrooms themselves. It is not as rich as compost that has not had something feeding on it. Bacterial slime – Leave a bucket of water that you have just done the washing in for a day, then run your finger around the edge. What you have there is bacterial slime. It is habitat that stops the bacteria from being washed away. It is their living area and part of what binds soil particles together. Try not brushing your teeth for a day – bacterial slime are quick at making their sticky glue stuff. This is what helps build soil structure.

Slime moulds (formerly fungi, but now protista) are predators of lots of other things. They looks like vomit, but are nothing nasty.

Other soil microbes
There are microbes in the soil that fix nitrogen like rhizobia associated with legumes. Archaea and eubacteria or cyanobacteria (sometimes called blue green algae) fix nitrogen and if you feed a lot of nitrogen to your soil you kill them and other things take over. Azotobacteria feed on sugar. There is a story of lime trees that had aphids and others that had no aphids. They were given the same fertiliser, water etc, but the ones with the aphids did a lot better. The sugar exuded by the aphids was going down on the soil, feeding the azotobacteria and they, in turn, were feeding the citrus roots. It is all about balance. The lateral spreading roots of a tree are the feeder roots – those that are in the healthy zone of the soil where fungi and bacteria also feed. People look at the drip line as to where the roots grow. The tree roots grow in air-filled, aerobic zones (avoiding compacted soil and anaerobic zones) and this is influenced by topography, adjacent structures etc. So the feeder roots are likely to follow an uneven pattern that does not follow the drip line. Tap roots are not feeder roots. They anchor the plant and get moisture. Feeder roots of vegetables in deep loams can go deeper than some trees.

Treating kikuyu infested clay
I apply a heavy dose of Rapid Raiser (high nitrogen, chicken manure based fertiliser), blood and bone, gypsum, coarse sand, covered with thick newspaper, then woody mulch and water. It is a completely dark situation. The kikuyu is not able to photosynthesise, it cannot produce sugars. Nitrogen will encourage growth, so it will draw on sugar reserves (eventually exhausting itself), but cannot produce sugars.

Soluble fertiliser in conventional agriculture
Conventional agriculture uses fertilisers that are soluble – the vast majority are salts. I look to use something that is 1-2percent nitrogen. If you use salt based fertilisers, you need to use a lot more nitrogen, because the salt will kill some of the bacteria, and fungi and so the soil is actually less productive from that sense. That is not a negative or a positive, just the reality. Using excessive soluble nitrogen (nitrates or ammonia or urea) is like going to McDonalds and having six hamburgers – it is a really big dose of food. Soluble nitrogen washes away and does not last long. You virtually need to feed at least every week with tiny amounts. We put our fertiliser out in big lots two or three times in the season. This gives them a big dose and then starves them for two or three months. Organic fertilisers break down slowly, feeding the soil, which feeds the plants.

What is protein?
Protein is nitrogen. So when you look at the microbes or bugs that are in the soil they are protein, so are mushrooms, fungi, single cells organisms etc. These life forms are also part of the fertiliser for the plant.

These life forms also have a lot of potassium. The more organic matter and organisms you have, the longer potassium will stay in your soil. If you are using a fertiliser that has a higher level of nitrogen than potassium, you are pushing that plant into a vegetative growth phase more than flowering phase. Potassium is very important when it comes to flowers and fruit. Seaweed has potassium.

When it comes to phosphorous, 90- 95% gets bound up almost immediately to calcium, iron and other irons in the soil and becomes insoluble phosphates. Superphosphate has sulphuric acid added to it to make it more soluble. Acidification is a long term consequence. Fungi can release phosphorous and feed it to your plants, so once you start looking at organic systems, you may not need to look at phosphorous as being such an important input as you do under conventional systems. Rock dusts (granite, basalt, other volcanic rocks), are the freshest out of the earth’s crust, but those minerals are not very soluble. It must be crushed into very fine powder and added to a compost. Alroc do quite good stuff with humates and rock dust (best form of phosphorous). A conventional farmer from western Victoria looked at use energy on his property – tractors, mechanical devices, diesel use etc, but 43% of energy use was fertiliser. That is why they have regulated calcium nitrate (saltpeter). It has enough energy to make bombs and that energy has come from gas. They take nitrogen from the atmosphere and make ammonia and urea which uses a huge amount of energy and much of this energy is wasted.

Fresh manures are very high in nitrogen, a lot of which is soluble nitrogen. That is why you can smell manure – with anything stinky you are smelling the loss of nitrogen. I do not use manures straight – for safety reasons, but also you are wasting the nitrogen. Use it in a compost. The nitrogen in compost will last longer in the soil than the nitrogen in the manure, because the nitrogen is in bacteria and fungi that do not get leeched or vaporised.

Hydroponics suggests we can grow plants with 16-17 minerals – not a healthy thing for us. Well over 60 are necessary/desirable. Selenium is an example. Only minute quantities are required, but it is a common deficiency in animals and humans.

Why do we graft? To get fruit earlier, to get consistency or to get a particular variety. When you add a graft you are putting on the variety you want, but you are giving that juvenile plant aged material from another plant so it becomes a mature plant and fruits earlier than a non-grafted plant. For successful grafting we need to have as much carbohydrate in the scion as possible for that type of plant. That does not relate to size. It relates to time of year or how you have prepared it. Dormancy, before a plant throws buds (flowers or vegetative), is the time that it has the most carbohydrate stored in the stem. Take cuttings and scion material in a dormant phase for the most chance of success in grafting because sugar that comes from the scion that forms part of the callous tissue. With evergreens, there are ways of preparing the scion material. Cincture the plant or cut the leaves off something that you are going to graft – 2-4 weeks before you graft, but leave the petioles. This helps concentrate the sugars. The rootstock needs to be in an active phase of growth in evergreens to get the most rapid healing. After care has a lot to do with your success. Protect grafts from sunlight, wind and ensure no shocks from changes of environment or temperature. Rub off anything that is growing from the rootstock below the graft. (more detailed information can be found in the CSIRO book Practical Hints for Budding and Grafting Fruit and Nut Trees.)

Question regarding fruiting of jujubes in Queensland. They have every chance of success (one fruits in Sunnybank). The biggest issue is the rootstock used to graft plants (Ziziphus mauritania) is a declared noxious weed.

Recommended reading on soil includes: Gardening Down Under by Kevin Handreck, Landlinks Press (2001) Designing and Maintaining Your Edible Landscape Naturally by Robert Kourick, Metamorphic Press (1986); Permanent Publications (2004) Composting: The Ultimate Organic Guide to Recycling Your Garden, Tim Marshall, Harper Collins/ABC Books (2008) Teaming with Microbes: A Gardener’s Guide to the Soil Food Web, Jeff Lowenfels and Wayne Lewis, Timber Press (2010) Teaming with Nutrients: The Organic Gardener’s Guide to Optimizing Plant Nutrition. Jeff Lowenfels and Wayne Lewis, Timber Press (2013).

Also any works by Dr. Elaine Ingham of the Soil Food Web.

Note:  With thanks to Annette McFarlane for writing up Harry’s talk.

Our mate “Harry” passed away 7th April 2019.

Below is a poem written by Kate Hubmayer from the Glandore Community Garden

19th May 1958 – 7th April 2019

As skinny as a worm With a smile as bright as Spring You were as subtle as a Sunflower

And had the energy of a Radish.

You could talk for as long as a New Guinea Bean And sing like a bird You were as funny as a Brussels Sprout

And as generous as an Olive Tree.

You were as feisty as a Chilli And as soft as a Guava You nurtured our soil with compost and worm juice

And enriched our lives with your knowledge and friendship.

Your passion for gardening has wound around us like tendrils
And we will keep on gardening, nourished by the memories.

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