By: Karin Lindquist
Battle River Research Group
Soil health sampling. It seems rather painful and boring; a bit of a chore when you're tasked with the job of finding a variety of farmers willing to allow you to come on to their land to do some soil health testing. In October 2021, that's exactly what I was busy with.
To tell you the truth, the experience was anything but boring. It was enlightening, encouraging, discouraging, humbling, exciting, and... a bit cold too. Late October here in Alberta is not exactly tropical weather. The year 2021 especially wasn’t so nice!
What is soil health testing? It's basically a comprehensive soil testing procedure that does a lot more than collecting soil core samples. There are three other elements: compaction reading via a penetrometer, water infiltration testing, and taking bulk density samples.
Perhaps the most exciting part is the water infiltration test. I'll get to that soon.
Soil health testing, overall, helps to assess how well the soil has been managed. It does not matter what kind of agricultural activity has been going on or what type of soil you have on your farm. It allows a "technician" like me to see how well (or badly) compacted the soil is, where the compaction layers are, how dry (or moist) conditions affect root penetration capability, how much litter and organic matter is present on and in the soil, what plant roots are doing or have been doing, and what type of soil is being tested. Soil health testing also includes a biological component where a small sample of soil is taken and used to assess what kind of biological community is present in the top three inches of the soil.
To do my testing, I must find a site that is even in topography, that is not at the very top of a hill or the very bottom in a low-lying area, such as an ephemeral slough or riparian zone near a creek, river, or lake. A good site can be chuck full of rocks or gopher holes; these matter less than what the area looks like in terms of how uniform the land is, as well as the vegetation in terms of usage (like on a pasture, for example). If there are a lot of hills, I like to choose a site that is mid-slope. Then I estimate a 30 metre by 30 metre (or 100 ft. by 100 ft.) area, often by stepping it out (rather than digging out a measuring tape and being far too precise than I should be).
Then the fun begins!
The penetrometer is the best way to assess soil compaction. It's an instrument that I poke into the ground in several random spots, pushing down on the handles until I get a reading at a limit of 300 psi (pressure per square inch). Three hundred psi is the highest limit that roots can exert when pushing into the soil to reach nutrients, moisture, and for the plant to increase its energy storage capacity. Because the area I live in has been so dry (average precipitation only 2 to 3 inches this entire growing season), most of the penetrometer depths I've been able to get have been no less than 1 inch (2.5 cm) and no more than 3 inches (7.6 cm). Rarely do I get depths greater than 6 inches; either it's a gopher hole I plunged into or some odd ephemeral slough area where I could push the probe down to 24" and still not get a 300-psi reading!
The penetrometer helps me determine what kind of soil cores I need to use to dig out soil samples. Two types of aluminum cylinders I used were the 0- to 3-inch shorty one, and the longer 0- to 6-inch cylinder (I also call them cores). Because the soils have been so much fun to hammer into, I must use the 0-3 core first to get the 0 to 3-inch soil layer, then use the 0-6-inch core to get a 3-6-inch soil sample. The 0-3-inch core sample is put in one pail, and the sample from the 0-6-inch core is put in another pail. I repeat this on 6 to 8 spots within my designated area. Always keeping the 0-to-3 and 3-to-6 samples separate, they get dumped (about 4 cups worth) into separate plastic bags. These samples are taken to the lab to get analyzed.
Why keep two different soil depths separate? Why not combine the two and make a nice 0 to 6-inch soil sample to bag up and be done with? The reason has to do with what's being analyzed at the lab. The lab does the standard test of acidity/alkalinity (pH), clay/sand/silt/loam analysis, electro-conductivity readings, salinity content, organic matter content, and some of the micro-minerals. Two different soil layers show different results in lab analysis, which gives you an idea of what's going on in the topsoil layers versus further down below the surface.
And yes, I said hammering. I tried using the stand-up, push-in probes however the soil was so dang hard and stubborn that I was bouncing around like I was on a horribly made pogo stick. I'm not light in bodyweight either, and I honestly couldn't get down past the first inch with our nice custom-made standing probes! So, out came the rubber hammer and the wood 2x4 to hammer in those probes.
Fortunately, one of the farmers I sampled for was very kind in suggesting I use a much heavier hammer--like a big ol' hand mallet--and allowing me to use a couple of solid oak boards instead. My soft-wood 2x4 made from spruce was so beaten up it splintered apart in just a few sites that I used it on. The heavy 4-lb mallet was great on soils where the rubber mallet was pathetic at trying to get the soil core any deeper than an inch or two.
What was fun about this second part of the soil health sampling game is how I was able to observe what--and how bad--the soil compaction layers were. Holy schmoligans there were some real humdingers, let me tell you! On a lot of fields, you wouldn't notice there was a compaction layer until you dug at most, 2 or even three inches down past the tilled soil surface. Many fields had a platelike structure down past that mark, where you could see how the soil doesn't have the natural, vertical columnar structure
One farmer I talked to was shocked to learn that many, many areas in the country--not just this province--have compaction issues. He believed that it wasn't a problem in this province. My experiences respectfully disagreed with him. It opened a great opportunity to discuss soil health and to start planting that seed about regenerative agriculture. With my observations, I shared with him how I've seen that the compaction is due largely to mechanical disturbance, pressure from heavy machinery on the land, and a lack of diverse vegetative species for long periods (I'm talking decades here). This led to a brief discussion on soil biology and polyculture cover crops. There seemed to be a little interest, but it wasn't my prerogative to push anymore than I needed to. Planting that seed was my mission, and I accomplished it.
Unfortunately, though, many farmers don't bother going out in their fields with a shovel to dig in the dirt and see for themselves what's going on beneath their tractor tires. That top two inches can fool anyone; anyone, that is, who won't go out to do some digging.
Compaction isn't just an issue in cropland. I've seen plenty of similar issues on pasture. Large cows, lack of species diversity, lack of or insufficient vegetative cover and plant litter left behind post-grazing, overgrazing, under-utilization where animals are a bit too careful in where they step as they graze, as well as how rainfall adds to capping and fusing soil particles, all contribute to compaction issues on pasture.
The type of soil has some impact on how likely a type of soil can become compacted. For instance, clay soils are more likely to have compaction problems than sandy soils. I say "some" because it's not the be-all-end-all factor. It's rather reductionist to isolate soil type as "the thing" to be why compaction occurs in the first place. As I alluded to above, management plays a far bigger role. Management, therefore, determines how well water is going to infiltrate into the soil depths.
My third task is the water infiltration test. I take a 4-inch cylinder and hammer it into the ground until it feels solid, where only one or two inches of the cylinder is kept in the ground. This prevents any water from leaking out from underneath, skewing the infiltration rate results. I then fill up a cup of water that stimulates one inch of rain and have my phone at the ready with the stopwatch timer app ready to go. As I pour water into the cylinder, I hit START on my phone at the same time, and the waiting game begins.
The water infiltration test determines how fast--or slow--water will trickle down into the soil depths. While it's not as good or entertaining as the rain simulator test in the videos below, it shows similar results in whether water can quickly move down into the soil depths, or if there's an obvious problem of runoff as rain from a wicked-awesome thunderstorm pummels down on the earth.
Roots and the rhizosphere's biological community play a big role in how water can infiltrate down into the soil. Not only that, but a lack of compaction layers also plays a significant role. Roots can only do so much; if they're only able to go down a few inches then go lateral (horizontal) the rest of the way, the water that infiltrates into the soil depths isn't going to move very fast or go down very far. A lack of organic matter in the soil surface is also a factor; if you don't have that, water is most likely going to run off rather than soak in.
When you have all the pieces in place for good soil structure, the rate at which water will infiltrate is going to be mind-blowingly fast. Like, less-than-30-seconds fast. That water isn't leaching away either; when there's that very important humus layer, it gets soaked up like a sponge. Organic matter acts as an awesome, all-natural sponge for holding water for a long period and slowly releasing it to the organisms that need it the most. Having a good aggregate structure helps.
When one or more of the pieces to a good healthy, structurally-sound soil are missing, water infiltration rates are going to be very slow. The slowest rate I had was one hour for one inch of water. It was on some rough ground with poor vegetative cover and a lot of soil capping. Most other sites ranged from 10 minutes to 45 minutes, tops. Not good. Yet, not surprising either.
Taking bulk density samples is the last on my to-do list. They show the lab compaction, as well as how dense soil particles are pressed together. It also shows if the soil samples themselves don't already, how well or poorly structured the soil is.
We ended up soil sampling a whopping 27 sites this past year! Per farm, we averaged approximately two sites. Some producers requested to have three or more sites tested, though we had to remind them that it wasn’t so much testing per quarter section, but for each area of their farm where they had different management practices. That certainly helped whittle down the number of sites we could have done this year… it is part of a province-wide benchmark project after all!
All of our soil samples—which filled three large coolers, no kidding—went to the Chinook Applied Research Association’s Soil Health Lab run by Dr. Yamily Zavala. I don’t know about the producers, but I can’t wait to see what the results will be once Yamily gets them all tested!
What I learned from doing all this is to put into perspective how management affects the soil. Now, in the last decade, we've become increasingly aware of the health of our soils, and how ignoring the literal "skin of the Earth" is no longer an option. For me especially, I enjoy reading and learning about soil science, soil biology and all that, but there's something incomparable with going out on a farmer or rancher's land--with their permission, of course--and doing the work to see what's going on beneath my feet.
I encourage you to go out when you get the chance to, with a shovel and see for yourselves what's going on with the piece of land you call home. Put your hands in it, smell it, see what structure is there; basically, and I know it sounds a bit crazy, let the soil speak to you. It'll tell you things that you probably don't want to know, but what you need to know.
By: Karin Lindquist
Battle River Research Group