The science behind soil health might be complex, but most of the tests showcased during the latest Manitoba Beef and Forage Initiatives workshop could be done with equipment bought from a dollar store.
“We have the ability to really investigate the soil ourselves,” Marla Riekman, land management specialist with Manitoba Agriculture, said. “You can use simple things like your senses — your sense of touch, your eyesight, your smell even, smelling the soil, listening sometimes for the presence of carbonates.”
Crop assessment and lab-generated test results played a part, but were not the focus of the June 27 workshop.
In one of the simplest tests for compaction, producers were instructed to take a spade of earth and drop it from waist height to see how it fractures.
Soil stability was met with a Slake test, wherein soil samples are submerged in a water-filled cylinder with a mesh basket, or an aggregate stability test, in which soil aggregates from different fields are separated into meshes (in this case, cheap colanders attached to a single handle) and dipped a set number of times into a water-filled trough. Both tests compare sample breakdown and may indicate susceptibility to erosion.
Hydrochloric acid will fizz in the presence of carbonates and may be used to measure drainage, the group heard. Carbonates in deeper soil have leached downwards with water and are thus a sign of proper drainage. Likewise, mottling (rust spots in the dirt) is a sign of frequent wetting and drying and may indicate improper drainage, Riekman said.
PVC pipe and plastic wrap also found their way onto the field to test infiltration. Plastic was placed inside a pipe entrenched several inches into the soil in order to stop splashing before water was poured in. Plastic was then pulled to expose water to the soil and infiltration was timed.
Riekman warned the test should be repeated several times, as the first will inevitably suck up water faster. Producers may also add a second ring of PVC and saturate the space between pipes, she said, as this will ensure that water poured into the inner pipe must travel down rather than spread out.
Texture and soil type will influence water capacity regardless of management, she added. Sandy soils, for example, will not hold as much water as clay loam, although both can be managed to be a healthier soil within their type, she said.
Darker colours, the mark of high organic matter, may also be tracked through a Munsell Colour Chart, attendees were told.
“This is a new field, or a new interest that people have in trying to quantify health of the soil and we’re trying to go over a few of the simple tests that farmers or agronomists can do on their own,” John Heard, soil fertility specialist with Manitoba Agriculture, said. “The thing we’ve got to remember is that it’s different than other tests. It’s both chemical, which is like the traditional soil tests, but there’s also the physical aspects — so soil structure, compaction, prone to erosion, etc. — and then there’s the biological.”
While soil biology may start and stop at microbes for some, Heard also pointed to plant growth, types of weeds and insect populations.
Weeds may indicate different problems with the soil, attendees heard. Foxtail barley, one of Manitoba’s most common weeds, may actually be a sign of salinity while acidic soils may have a wealth of orange hawkweed, compacted soils may grow plants like pineapple weed, strawberries and dandelions may herald a lack of phosphorus and farmers with a pigweed or lamb’s quarters problem may want to cut back on nitrogen.
Showcased tests were relative measures, both Heard and Riekman stressed, useful in comparing field-to-field samples or changes over time, but less scientific than lab tests.
“There’s no single measure for soil health and, for many of these, I think we don’t have standard book values for what a good number is,” Heard said. “We talked about 10 earthworms per square foot as a nice number, but we don’t have nice numbers for all these other practices.”
Growing on fungus
In contrast, mycorrhizal fungi cannot be detected by the five senses, although organizers suggested that soil activity, including mycorrhizal activity, could be highlighted by burying a swatch of cotton and measuring decomposition — a nod to the “Soil Your Undies” campaign that spread through the Soil Conservation Council of Canada this spring.
The fungi have been tied to the ability of some plants to access phosphorus at early growth and have proven susceptible to soil disturbance, making them one of the often repeated arguments for reduced tillage.
Corn and flax, some of the most dependent crops on early phosphorus, may be stunted if they follow a non-mycorrhizal crop. The commonly termed “corn after canola syndrome,” occurs when fungi, dormant after a year under canola or other brassicas, do not activate in time to facilitate early phosphorus access.
Where are you testing?
While aimed at on-farm relative measures, topics also veered into lab testing, proper testing procedure, an in-depth look at the services and methodology of various labs.
Attendees got a first-hand look at landscape variability as two holes less than 50 metres apart showed wildly different compaction, drainage, and black soil horizons.
“Measures like, say, soil carbon, organic matter, things like that, are extremely variable across the field and it takes a lot of samples in order to capture that variability,” Riekman said.
Researchers estimate that it would take 300-500 samples to eliminate all variability in a field, compared to the 15-20 recommended by Agvise Laboratories for composite sampling or benchmark sampling as suggested by the Manitoba Soil Fertility Guide.
Riekman advised sampling away from low-lying or saline areas as well as eroded knolls.
“Look at the mid-slope. What’s kind of most representative of the field?” she said. “We still might want to know what’s happening at the top of the hill and at the bottom of the hill, but we might sample those ones separately.”
Tests for organic matter and nutrient levels are common, but a number of labs have begun to include microbial profiles, aggregate stability, root health, texture and pathogens, among other measures.
But while such tests give concrete numbers, both Riekman and Heard warned that results are not customized to Manitoba soils, which are young, glaciated, have slower mineralization rates and freeze for months of the year.
In one instance, she said, university researchers were advised not to apply additional nitrogen, but tests were based on soil far to the south. The resulting crop failed.
“It’s not to say that these soil labs and things that are out there that do soil health testing aren’t useful,” Riekman said. “I think it’s still a bit of an immature science. We’re still working towards being able to have enough data coming from that side of information to really start creating recommendations, but we’re still a few years away from that.”
Organizers hope to better translate test results for Manitoba in the future. Workshop attendees were encouraged to send samples to various emerging labs. Riekman says she intends to bring the group back together later this year to analyze results.
“It’s just a lot to take in at one time,” Nathan Dmytriw said of the workshop.
Dmytriw farms north of Brandon and noted that discussions on compaction, microbiology, soil horizons and different testing techniques caught his interest.
Riekman and Heard noted that compaction risk was highest in moist, not wet, soils and that 80 per cent of compaction damage is caused in the first pass, giving credence to reduced traffic management plans, particularly on forage land which sees multiple cuts.
Linda Nielsen of Starbuck also said she found the day beneficial.
“We’ve got our son who’s going to farm probably someday. He’s doing a little bit of farming so we’ve got to take care of the land,” she said.