pH in a Biological Farming and Gardening System

Biological farming

Bacteria and fungi have been on this planet for 4 billion years. Predatory organisms joined them 1 billion years later and made nutrient cycling on a larger scale possible. When plants with roots made an appearance another 2 billion years later, there was no need for them to make strong enzymes to dissolve rock in order to extract nutrients from that parent material. They tapped into a system where nutrient cycling was already functioning. A mutual benefit started to happen as the plants started to photosynthesize and produce sugars.

A proportion of those sugars (exudates) are released through the roots to attract beneficial microorganisms to the root zone. They act as a food for bacteria and fungi and in return the bacteria and fungi protect the roots and deliver vital nutrients to the plants.

There is no need for us to go into a functioning ecosystem like a mixed species forest in order to feed the trees with nutrients like nitrogen, potassium, or phosphate or to regulate the pH in that system. Nutrients are naturally made available to the plants by an intricate soil food web. Organisms in the soil eat, digest, dissolve and break-up organic matter, and ultimately get eaten so nutrients can be released and made plant available again. They also regulate the pH.

In a biological farming and gardening system the intricate relationship between plants and soil microbiology is acknowledged, fostered and enhanced by making compost, compost extract and compost teas.

Fungal dominated system

In a forest system fungi are an integral part and make up the majority of the microorganisms. The fungal to bacterial biomass is 100 to 1000 or more fungi to one bacteria. The fungal network connects trees and is able to send messages and nutrients from one tree to another. Ecologist Suzanne Simard shares her 30 years of research in Canadian forests. Her TED talk “How trees talk to each other” is worth watching.

Perennial plants like to get nitrogen dished up as ammonium (NH₄). When nitrogen is released by the metabolism of protozoa and nematodes it is released as ammonium, so perfect for perennial plants as they can take it up as it is. Soil microbiologist Dr Elaine Ingham from the Soil Food Web Inc. explains: “Now that perennial plant is going to be making certain that it’s growing fungi throughout most of that root system because fungi, aerobic fungi, are going to maintain soil pH between 5.5 and 7. If those fungi are keeping it in that slightly acidic range, that means the nitrifying bacteria (see below) can’t perform their function, and that NH₄ is going to stay as NH₄.”

Bacterial dominated system

All our annual vegetables and crops prefer their nitrogen in a nitrate form and cannot handle ammonium. In a bacterial dominated system however nitrifying bacteria take that ammonium (NH₄) and convert it into nitrate (NO3). They work at a pH greater than 7. Aerobic bacteria in the soil are creating glues to glue themselves onto things around them. These glues are alkaline and therefore the pH is naturally above 7 in a bacterial dominated, aerobic system. The plants will make certain to put out the appropriate exudates in order to attract bacteria into the root zone and maintain a slightly alkaline pH so that nitrifying bacteria can perform their job.

Altering the pH

Fertiliser companies argue that some nutrients are not available at a certain pH and that most crops do better when the pH is between 6 and 6.8. The rising of the pH is achieved by applying lime, often done in big quantities to achieve a “sweeter” soil. It’s also worth noting that liming recommendations are generally based on one pH test. But testing several times a year reveals that pH can change significantly during a growing season and it can be different in different parts of the root zone of one individual plant at the same time. Lime applied in big quantities destroys the soil life just as chemical fertilisers do. Same applies to gypsum, ammonium nitrate and phosphate fertilizers applied at high rates. Lime is basically a salt, as it is an inorganic compound that dissolves in water. When we apply too much lime, then water is prevented from being available to the soil life because it is bound by the lime. When lime is applied it needs to stay below 100kg per hectare so it doesn’t wipe out the soil microbiota.

In our food production system at KoruKai Herb Farm we grow strawberries and blueberries. The general recommendation is that they like acidic soil and that the pH needs to be modulated every year in order to achieve that. Sulfur, acidic fertilisers like ammonium nitrate, ammonium sulfate, or sulfur-coated urea, diluted vinegar, pine needles and coffee grounds are recommended for commercial and home gardeners alike. The fact that some of these amendments can be damaging to the aerobic bacteria and fungi in the soil is most (if not all) of the time ignored. A mistake that makes the system dependent on the continued application of fertilisers in order to feed the crops as natural (free!) nutrient cycling has been stopped.

Biology in the soil affects pH

In my opinion simply measuring and modulating the pH is the wrong end of the equation to look at. Strawberries and blueberries prefer a fungal to bacterial biomass of 5:1. Five parts fungi to one part bacteria is a fungal dominated system. A fungal dominated soil will naturally be in the acidic range and will feed the appropriate nutrients to the plants, i.e. nitrogen is served in ammonium form. At KoruKai Herb Farm we create a system by design that serves the plants well. For strawberries and blueberries we have buried copious amounts of wood in order to feed fungi (they have the enzymes to break it down, bacteria do not, so this selects for fungi and they will thrive in that system) and have created a huegelculture bed.

Huegelculture bed in the making at KoruKai Herb Farm.
The buried wood provides ample food for fungi to thrive, creates an acidic pH and feeds strawberries for years to come without any input.

Yes, pH is important and we should not ignore what it is telling us, but we need to modulate it with the soil food web in mind and not by ignoring the intricate web altogether.

If your soil or compost pH is below 5.5 than you need to put measures in place to stop this from happening, i.e. drainage of waterlogged conditions in anaerobic soil or aerating/turning an anaerobic compost pile. The addition of microbes will bring that shift naturally and create a pH suited for the environment and the plants.

Bruce Tainio, an American agronomist did a speech at the 2005 Eco-Ag Conference about soil microbiology. He has been doing research in Washington State with 48 farms, where they measured soil pH extremes of 9 and 3. An alfalfa grower asked Bruce for advise as his crop didn’t grow well. They measured a soil pH of 4.5, which showed that the soil was in trouble. They applied microbes and enzymes to stimulate the indigenous microbe population, which brought the soil pH to what they determine as a balance scenario. Bruce suggests, “Microbiology of the soil will adjust the soil pH from these high extremes or low extremes if they are given the chance to work that way.”

Compost extract for our paddock to increase fungi and bacterial numbers as well as
predatory protozoa and beneficial nematodes.

Dr Elaine Ingham explains in her “Life in the Soil Class”, “Exit that concept that we should be controlling nutrient availability based on shifting pH because that’s just going to totally destroy the soil, and we put ourselves back into this chemical addiction mode that we’re in. We need to put the biology back out there and let the plant start managing its own biology. Our job is to put the maximum diversity, the microorganisms back out into that soil, around the root systems. Let the plant take care of itself.”

Applying biology and the appropriate foods to feed them is the biological way to alter pH in an agricultural system. In the picture above Kai is applying a compost extract on the farm. A biological soil test has shown that we need way more fungi to get an equal bacterial to fungal biomass and we were also lacking predatory microrganisms like flagellates, amoebae, and beneficial nematodes. The brew that we did for this paddock was high in fungal strands and had those nutrient cyclers present that we were lacking. We also applied solid humates (50kg per ha) to the paddock and liquid humic acid to feed the fungi in the soil and keep them happy.

By applying the missing biology, we have seen a massive improvement. This is what the area looked like before applying biology. The soil test showed pretty much no fungi and very little protozoa, some root feeding nematodes and bacteria.


The photo below shows lush, green growth, a high clover content, yarrow and plantain. This was after 2 applications of compost extract. The clover also provided a massive food supply for our bees over that summer and for the first time we could harvest 25 kilos of clover and kanuka honey from one hive. Win-win for everyone.


Trust in nature and help her along to restore soil, ecosystems, natural cycles and regenerate the land with those tiny critters called soil microorganisms.

To learn more about the Soil Food Web, please have a look at our online seminar in July: Biological Gardening and Farming ONLINE courses

For a biological analysis of your soil please contact Cherryle Prew from the Soil Foodweb NZ.

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