Miranda Hart digs dirt.
The associate professor in UBC Okanagan’s Irving K. Barber School of Arts and Sciences is a researcher and naturalist who has dedicated her career to studying microbes in soil. Specifically, she investigates how soil biodiversity helps ecosystems function, and what happens when we destroy this life in our soils.
While the focus of her research—soil microbial communities—may sound complex, it’s happening in every backyard garden around the world. We asked Hart, who teaches biology, to break down her science for people who love mucking about in the dirt as much as she does. Here are some tips for gardening, whether it’s flowers, a crop of vegetables in a community garden or a few herbs in a window basket.
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We’ve heard recently that some researchers suggest tilling, or overtilling, is not effective and is actually harmful to soil. Yet, we’ve been doing it for hundreds of years. What are your thoughts on this?
This is not easy to answer. Tillage has been with us as long as agriculture—but it is hard on the soil. It leads to loss of topsoil (erosion) and also disrupts the network of roots and fungi below ground. This leads to a less resilient system and therefore, less efficient?
For intensive agricultural systems or gardens, this might not be a problem because you’re adding nutrients and biocides.
The main reason we’ve been able to move to ‘no till’ agriculture is due to herbicide use. Currently, farmers control weeds with herbicides, not tillage. But this is not sustainable, because weeds develop resistance to herbicides. Plus, there is increased scrutiny on the environmental and health consequences of using herbicides.
In short, if you have a garden, weed by hand. If you have a farm—you need to weigh your weed problem versus how much topsoil you have.
Your work examines arbuscular mycorrhizal fungi (AMF) and how it benefits plant nutrition and crop production. Your latest research examined how a commercial AMF inoculant worked in different grain-cropping practices. Did the commercial product out-perform the natural process?
No, the commercial product did not perform better than control plots—we added a native AMF and also had plots without AMF additions. I think the reasons are two-fold: 1) The AMF isolate failed to establish on many sites. 2) the resident fungi were probably already doing a good job and I don’t think the inoculants were necessary.
In general, if your soil is in pretty good shape and you have had plants growing on it recently, you likely have resident fungi that are good enough and you don’t need to add anything else.
Is commercial fungi perhaps the way of the future?
Not yet. We still don’t understand what factors allow a fungus to establish in foreign soil. And even if they do establish, are they good for that soil? Or that particular crop?
It’s hard to imagine that there is a ‘silver bullet’ fungus that will be a good fit with all systems and cropping types. Further, we don’t know what happens to these fungi in natural ecosystems—can they become invasive? Do they affect the biodiversity of resident microbes and plants? We need to answer these questions before I can recommend their use in the field.
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Is it possible to transfer your knowledge of soil health to information a backyard gardener could use?
Absolutely. The key to ‘healthy’ soils is to promote a biodiverse ecosystem that is well adapted to the soil and climate. Use native plants wherever you can, and take it easy on the inputs (nutrients and fertilizers) because plants that are adapted to our climate are not used to high levels of fertilizer.
However, for a production garden, then you’ll definitely want to augment nutrients. I recommend organic fertilizers over synthetic, such as compost or manure, since they will stimulate the soil food web by including carbon for the microbes to eat. This leads to higher biodiversity in your soils and more resilient plants.
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