The key workforce in the soil consists of some of the smallest plants and animals on earth. These includes bacteria, fungi, algae, protozoa, nematodes and earthworms. A core principle in any farming operation should be to care for this workforce so that it, in turn, can care for the farm.
“The main paradigm shift required to head down this path involves a recognition that the soil is a living organism and that we stand to earn a better living if we nurture that system,” says Graeme Sait, CEO of Australian firm Nutri-Tech Solutions.
The weight of the biomass linked to this subterranean ‘livestock’ in our soils, he says, often physically outweighs the livestock above ground.
However, this diverse soil life features organisms that are both beneficial and toxic to animals and people. For example, anaerobic bacteria, which thrive in compacted soils and release hydrogen sulphide that smells like rotten eggs, and butyric acid, which smells like vomit, are both toxic to plant growth.
Another group of soil organisms, facultative anaerobes, are also harmful. Two well-known types are Escherichia coli and Enterococcus, which can cause severe health problems in people and animals. One of the many potential sources of Enterococcus is vermicompost, if the food source for the composting worms has not been subjected to the heat produced in the initial stages of conventional composting.
“Then there are the pathogenic organisms that cause massive crop losses and which demand chemical intervention,” says Sait. “Thankfully, all of these less desirable organisms can be managed if we understand soil balance.”
Smells as signposts
One of the many beneficial bacteria in soil is Actinomycetes, which emits volatile chemicals that provide the ‘fresh earth’ smell that farmers and gardeners find so appealing. According to Sait, Actinomycetes is a ‘signpost’ organism indicating good soil health. A soil without a fresh earth smell contains little or no beneficial soil life. These deprived soils inevitably require more chemical interventions, which increases production costs and reduces profitability.
“There can be as many as 2,5t/ha of bacteria in healthy soil,” explains Sait. “These organisms retain nutrients in their bodies, reduce leaching and remove most toxins from the soil. They produce a sticky biofilm that acts like water crystals to retain moisture. This can help to significantly reduce irrigation requirements.
“Soil bacteria are also key recyclers of nitrogen. They have the tightest carbon (C) to nitrogen (N) ratio of any creature on the planet. Their C:N ratio of 5:1 means that their bodies effectively contain 17% nitrogen. This means that the bacterial biomass in your soil can be storing the equivalent of almost a ton of urea.
“Farmers can easily, and very cheaply, improve their soil’s beneficial bacteria by brewing up their own populations in a drum or vat and then applying this new workforce via the irrigation system.”
Soil algae are plant-like organisms that contain chlorophyll and can photosynthesise. They also exude sticky substances that contribute towards binding and aggregating soil particles into a desirable crumb structure. According to Sait, healthy soils can contain up to 600kg/ha of algae in just the top 15cm of the soil profile, and it is now believed that they produce 20% of the nutrients required by other beneficial soil life.
If these beneficial soil organisms are well-fed and in abundance, it is more difficult for soil-borne pathogens and damage-causing animals to compete and survive. Sait cautions that herbicides can kill soil algae on contact, resulting in less food for beneficial soil life. This reduction in beneficials can provide harmful soil life the opportunity to flourish.
Balance: the key
“Soil fungi convert hard-to-digest organic matter, like crop residues, into forms that other soil organisms can utilise,” Sait continues. “While soil bacteria can release an alkalising slime that tends to raise soil pH, soil fungi release acids into the soil which reduce soil pH and solubilise locked-up phosphate.
“A single fungus specimen can cover the area of a football field. When soil fungi die, their decomposed hyphae leave an extensive system of tiny tunnels in the soil. These tunnels are perfect for allowing water and air to penetrate into the soil. Soil fungi’s hyphal masses (mycelium) also retain nutrients, which helps to reduce leaching.”
Sait explains that some soil fungi trap destructive root-eating nematodes and feed on them. Soil fungi are also particularly important for the storage, availability and delivery of plant-beneficial calcium (Ca). When soils with high Ca levels produce plants with low Ca levels in their leaves, this may indicate low fungal activity in that soil.
Soil fungi populations can be boosted by feeding them complex carbohydrates. These complex carbohydrates can be found in humic acid, kelp and aloe vera. Commercially available water-soluble derivatives of these products can be applied through irrigation systems or through tractor-drawn spray rigs.
“Mycorrhizal fungi are the greatest soil savers among beneficial fungi species. They attach themselves to plant roots in a mutually beneficial relationship. These remarkable creatures are responsible for over 30% of the planet’s humus, “ says Sait.
Plant root system: there can be as much as 2,5t/ ha of bacteria in healthy soil. These organisms retain nutrients in their bodies, reduce leaching and remove most toxins.
Soil life analysis reveals that up to 90% of mycorrhizal fungi have been destroyed by modern farming techniques. “The loss of two-thirds of the world’s soil humus to the atmosphere can be directly linked to the decline in myccorhizal fungi,” says Sait. “They offer so many benefits and can provide solutions to many of our problems. For example, myccorhizal fungi improve the plant roots’ efficiency for absorbing soil nutrients, they boost plants’ immunity to attacks from pests and diseases, and they offer primary protection against damage-causing soil nematodes.”
Another class of soil organisms are single-celled creatures called protozoa. Sait points out that a loss of soil protozoa not only requires a farmer to add more chemical N to the soil, but beneficial earthworm populations will decline because they feed on protozoa.
“One strategy for restoring soil protozoa numbers, thereby increasing earthworm numbers and soil nitrogen recycling, is to make and apply lucerne tea,” he explains.
“Chemical-free lucerne hay harbours huge numbers of protozoa because the hay is high in protein. Place the lucerne hay in a drawstring bag made of shade-cloth. Take some liquidised fish and molasses and mix them into a large tank of water. Submerge the bag of lucerne hay in the tank. Aerate the tank with a pump, venturi or aquarium bubbler and after 24 hours apply the liquid to your soils.”
Sait says he has seen significant reductions in chemical nitrogen requirements following applications of lucerne tea.
Explaining the mechanics of this phenomenon, he says that protozoa have a C:N ratio of 30:1, which means that they must consume six bacteria (at C:N 5:1) to obtain sufficient C for their own survival. Protozoa need only one unit of N from the bodies of every six bacteria, so they excrete the remaining five units of N. Plant roots readily absorb this. In the absence of protozoa, the N stays in the bodies of the bacteria, leaving a large quantity of urea in the soils that cannot be utilised by plants.
According to Sait, 80% of soil nematodes are beneficial to the soil. They disappear, however, from compacted soils and, following this, N recycling disappears too. This is because nematodes have a C:N ration of 100:1. Like protozoa, they need to consume bacteria to access life-sustaining C. They need to eat twenty bacteria (C:N 5:1) to achieve the hundred units of C they require. However, they have no need for the bacteria’s N component, and so they excrete this into the soil, thereby recycling the N for crops and other plants.
Sait explains that, due to ignorance of the importance of soil life, farmers mistakenly use nematicides, which kill all nematodes good and bad, thereby creating an opportunity for damage-causing soil nematodes to begin increasing in number. The primary natural control of root-eating nematodes are the predatory nematodes that constantly feed on them. Ironically, the first nematode to breed back after nematicide application is the notorious root-knot nematode because it no longer has any predators or competition.
“The best way to control damage-causing nematodes is to encourage populations of beneficial soil nematode species that will either feed on damage-causing nematodes or simply out-compete them,” he says.
One of the most beneficial soil creatures, according to Sait, is “the mighty earthworm”. The 7 000 known species shred soil organic matter and compost it four times faster than conventional composting. They also aerate soil, increase its water-infiltration and water-holding capacity, aggregate soil particles, move minerals from deeper in the soil profile up to the plant root zone, and introduce beneficial microbes.
A number of additional facts about earthworms should motivate farmers to encourage these animals to their soils, Sait says. The worms’ castings contain seven times more phosphorous (P), 10 times more potassium (K), five times more N, three times more magnesium (Mg), and one-and-a-half times more Ca, than the surrounding soil. They are, in effect, a living fertiliser factory.
“If you could consistently find 25 earthworms per shovelful of soil, those earthworms would be contributing 300t/ha of castings to your soil. This is the Holy Grail of biological farming, because earthworm castings cost at least AUS$100/ha (R947/ ha) so you just scored AU$30 000 (R284 000) worth of free fertiliser. This means huge savings on chemical fertiliser. In fact, it’s not required,” Sait says.
Earthworms also have a calciferous gland that adds calcium carbonate (CaCO3) to the soil.
“They don’t just offer free fertiliser, they’re like having your own lime works,” he enthuses.
“Modern agriculture has extracted a harsh toll on beneficial soil organisms. These organisms can, however, be regenerated in the soil. Humates, fish-based products and kelp-based products can be used to feed the existing soil workforce and it’s an inexpensive, repopulating strategy to brew up your own new recruits.”
This presentation was given at a soil health seminar hosted by Zylem, which represents Nutri-Tech Solutions (Australia) and Brookside Laboratories Incorporated (USA) in South Africa. For details on Nutri-Tech Solutions and Brookside Laboratories in South Africa, phone Zylem on 033 347 2893 or email [email protected].