Taking a microscopic look at soil

When it comes to new technology in horticulture, the biggest developments are actually very small; in fact, they are practically invisible. Soil microbes are so tiny that it would take more than a thousand of them lined up in a row to stretch across the period at the end of this sentence.  Just a teaspoon of soil can contain billions of bacteria and metres of fungal hyphae strands, and they play an integral role in soil health and plant growth.

This microscopic world has been relatively unknown to us but, in the last decades, genetic sequencing has opened up a new frontier of exploration. DNA barcoding can identify nearly every species in a soil sample, and now researchers are getting a better understanding of which microbes are doing what. 

Dr. George Lazarovits, research director at A&L Biologicals, is doing just that. A few years ago, his team compared two management systems near Dunnville, Ontario. Dean Glenney used no-till, controlled traffic, alternating strips of corn and soybeans, and relatively low inputs for his 300-bushel corn yields.  By comparing with a neighbouring field, Lazarovits discovered that the microbial communities between the farms were dramatically different. “In Glenney’s corn field there were more microbes but less diversity, as if they had reached a critical mass in order to create a function for the plant,” he explains. 

The project has now scaled up to more than 40 corn fields across Southwestern Ontario. The team flies drones to get maps and compares samples between the highest and lowest yielding areas of each field. “We determine which species are present, but what we really care about is what functions are being amplified in that soil,” explains Lazarovits. “We ask how many nitrogen-fixing genes are present or how many phosphate-solubilizing genes, for example.”

Research is revealing the complexity of interactions within this invisible ecosystem. Lazarovits points to a Japanese study, which determined that millet inhibits the ability of bacteria to convert ammonium to nitrate. His own research at Glenney’s farm found a cover crop of Austrian winter peas gave a 15 per cent yield bump in the corn over the test strip, averaging 345 bushels.

Microbes are crucial to soil and plant health in horticulture as well. They decompose residue to build organic matter, work to sequester carbon, cycle nutrients, and suppress diseases.

For a farmer, the best way to understand this biology is under a microscope, says Mike Dorian of Living Soil Solutions in Alberta. Dorian took the stage at the Compost Council of Canada’s 26th annual conference in Niagara Falls in September and explained how manure, compost and other organic amendments are also important for feeding this invisible web of life. 

Even with a $300 microscope at 400x magnification, farmers can see the ratio of fungi to bacteria, and this ratio is important for plant growth. “Bacterial-dominated soils are weedy,” says Dorian; whereas, fungi thrive in soils with higher carbon and less disturbance. Fungi can drastically increase plant growth by acting as an extension of the roots, finding nutrients and moisture. 

Dorian emphasizes the importance of the whole soil food web: bacteria, fungi, protozoa, and nematodes, as well as the beetles and earthworms we can see. They are working together and eating each other, to break down organic matter and make it into plant available nutrients, he explains. And by colonizing a plant’s root zone, these microbes are also defending it from pathogens. 

Lazarovits, also headlining the compost conference, emphasizes compost as a disease suppressant as well, giving examples of high-value crops around the world and at what cost farmers are using chemical fumigation or steaming to control soil-borne disease. He has demonstrated that the beneficial microbes present in many types of compost are able to control disease, and more cost effectively. 

He cites a turf grass trial in which 10 pounds of compost for every 1000 square feet replaced the need for pesticides to control dollar spot and Pythium blight. Doing the math, he estimates that 435 pounds of compost saved $600 worth of pesticides on each acre. “So what is the value of compost here?” Lazarovits challenges. 

The Compost Council of Canada will be offering courses for Ontario farmers on soil health and microbes, including hands-on experience with microscopes. It is being offered with support from the Agricultural Adaptation Council and Growing Forward 2 funding.  Information will be posted at www.compost.org in early 2017. Stay tuned! 



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Thursday, October 20, 2016

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