Spring fieldwork has begun!

No amount of cold, miserable wet weather can ruin working in this environment ūüôā

Last week we had our first day of the season out in the field (literally). Six of us worked together to measure out the test plot, take some initial soil samples, and do a few other assessments and measurements to get a good overall impression of the field. It was a pretty miserable day in terms of weather, with under 10 degrees Celsius and that fine wet mist that is almost rain but not quite. In weather like this, the cold creeps its way right through to chill your bones. I volunteered to run around hauling jugs of water just to get my blood moving a bit. Despite the weather, I had a great time. I always love fieldwork and have done enough of it to know that the conditions are usually far from luxurious, and it was great working with a big team since I do most of my work on my own or with just one other person.

I can’t say much about the project, since I don’t actually know all the specific details yet, but I do know that there will be a LOT (I think over fifty) of sub plots within the test field.¬†It’s awesome to see such a big project happening, but I will be a bit¬†cross eyed after analyzing that many¬†samples with¬†the microscope.

We did a number of tests to evaluate the soil on site: looking for soil life at a macro scale, checking the soil structure including compaction and drainage, and making qualitative analyses of the soil by looking at it, smelling, and feeling it. When we cut chunks out for qualitative analysis, we first lay them on a large¬†paper to get a general overview of how it looks. We look at the colour, check for organisms like earthworms or arthropods, check for layers of old organic matter that hasn’t decomposed well, and we look at the structure. How well does the soil hold together if you pick up a clump and gently squeeze it? Can you roll it and make a sausage with it? How does the soil feel when you roll it between your fingers? How does it smell? We make notes on many different features of the soil, then dig out¬†another chunk¬†and drop it from standing height to see how well it holds together. Good soil should have a nice aggregated structure that doesn’t make rock hard clumps¬†but clumps shouldn’t¬†disintegrate like sand either. In this case, since we had all day and a big team, we also dug up a bigger¬†pit to view and measure the soil layers in situ. Obviously this is a very subjective way to evaluate the soil, but it is valuable nonetheless and we include this information in our overall assessment of the soil.

*I realize I haven’t actually written a post about what we do at my job, but basically we are a nonprofit organization that does¬†various research projects looking at what methods we can use to evaluate soil quality and improve soil health using biology, rather than the conventional chemistry approach. At this time we are not a service that goes out and evaluates peoples’ soil for a fee. ¬†

Here we’ve cut out a chunk of soil and laid it on a large paper, to do some qualitative analyses

We used a compaction meter to see if there was a compaction zone (possibly caused by plowing). The meter is just a long rod with two handles at the top, which is pushed down into the soil. As the rod is pushed down, a needle moves up on a dial as the pressure increases. When it becomes hard to push, the needle will move up to the red zone. Once it hits that point, we stop and pull it out, then measure how far down the rod went. Some places in this field were compacted about 23cm down, but the depth was quite variable, and occasionally the soil was so soft it went down the full length of the rod and never left the green zone, so we did not find an established hard pan layer in the topsoil.

This is a top down view of the compaction meter.

Another method we use to assess soil is the infiltration test. This gives us some idea of the general soil structure and health of the soil ecosystem by telling us how well the soil drains. Soil drainage is a measure of how well the soil absorbs and retains water. If soil does not drain well, water will flow off the land very quickly, carrying loose topsoil and soil nutrients away with it, depositing them in local waterways. This is one of the big contributors to soil erosion, sedimentation in water bodies, and nutrient pollution caused by agriculture. Well drained soil will reduce the need for irrigation as it retains more water, while also letting it soak deep down to slowly recharge underground aquifers instead of pooling on the surface and flowing off the field.

For the infiltration test, we use cut pieces of a large metal pipe hammered into the ground to isolate a part of the soil. (Ideally this is done with a slightly more elaborate system using two cylinders doubled up on each sampling point to avoid water leaking out the side, but this is the method we have found to work the best for us so we consistently do it this way and compare the results against each other). We then put a sponge in the bottom of each cylinder to avoid any compaction caused by the water impacting the soil, and pour water into each cylinder. We remove the sponges, measure the water level at a starting point, then wait three minutes and measure again, then just find the difference between the two points. This way we can find out the rate that water drains into the soil.

In heavily compacted areas with little organic matter, such as conventional grain fields¬†where large machinery has¬†been, we have seen soil that did not absorb any water at all in the three minutes we measured. At the other extreme, we have measured forest plots where the water ran through so fast we had to¬†measure it in just¬†one minute, since the cylinders weren’t big enough to hold three minutes worth of water at that rate.

Infiltration tests were done in different locations to see how well the soil drains.

The owner of the farm was kind enough to plow a few rows, right beside the test plot. Not sure if there was a reason for this, but I’m glad I had rain pants and waterproof hiking boots.

I don’t mind working out in the rain when there are beautiful views like this in every direction.

My mini home lab where I do my microscopic analysis of the soil samples

This initial round of microscope analysis only required six soil samples to get a general picture of the field starting out, and from what I could see there is some life in the soil to begin with which is always nice. Sometimes farm samples are incredibly dull to look at; usually they are basically nothing but bacteria and mineral particles.

In these samples there wasn’t much, but I did spot a few protozoa and a rotifer, which always makes my day. Other members of the team took soil samples home for different kinds of analysis, including some chemistry to check pH, nitrogen levels, and things like that. It will be very interesting to see if the compost and other treatments will have an effect on this soil. It will be many months before we find out. Despite having worked here since 2013,¬†is the first time I’ve been here from the very start of the season, so I feel a lot more involved in the projects and I’m looking forward to seeing how they progress.

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Field vs. Garden Soil.. a closer look

I analyzed the field and garden soil from the previous post, and it’s clear under the microscope that the structure is quite¬†different between them. This is probably why there was a big difference in clarity when the samples had settled.

A single soil sample can vary quite a bit under the microscope, so I included two photos from each one to give a general idea of how they looked. I just held my iPhone up to the eyepiece on the microscope to take the pictures, so they are not the greatest quality. All photos are taken at 400x magnification.

IMG_3746

Field Soil

Garden Soil

Garden Soil

Field Soil

Field Soil

Garden Soil

Garden Soil

What causes this difference?

The answer is probably humus. Humus is essentially the end of the line for living organisms. When something dies (a plant or animal), it is decomposed by a progression of smaller and smaller organisms. This process breaks large organic molecules down into smaller ones. Then, the material goes through mineralization and humification, both done by microorganisms. The microbes will transform organic matter into inorganic components (mineralization) and humic substances (humification). After humification, the material is considered stable (to varying extents), which means it has reduced or lost its potential to be broken down or mineralized further.

Humus benefits the soil in a number of ways. I might write a more in depth post on humus in the future, if there is any interest in that. For now, I’m just interested in¬†the binding ability, since this is what¬†most likely¬†created the¬†difference in clarity between the above samples. Humus causes¬†particles in the soil to become¬†organized into clumps, which improve the soil’s porosity and ability to hold water. You can see that the field soil, which has less organic matter, is just a dense carpet of small particles, while the garden soil is significantly less cluttered.

Microscopic organisms¬†that live¬†in the soil actually live in water. They survive in the thin film of water that surrounds soil particles, so despite¬†living in soil, they actually swim to get around. Imagine a creature like the ciliate pictured below swimming in the soil on the right, compared to the soil on the left. Even if the amount of food available for it in each soil was the same, it would probably survive better in the “cleaner” soil, simply because it would be easier to get around and hunt. It would be like the difference between running on sand versus a paved surface.

This is a ciliate, a large predatory protozoa which was found in the garden soil.

The large round thing in the middle is called a ciliate; a large predatory protozoa which was found in the garden soil.

So even with this single factor considered, it would make sense that only a dense population of bacteria and a few tiny flagellates were found in the field soil. There is probably a lack of predation from creatures higher on the food chain (such as protozoa which prey on bacteria), which means there may be less biodiversity in this soil ecosystem. The garden soil had many different kinds of bacteria, but fewer of them overall. I found almost no protozoa in the field soil, but many different kinds in the garden soil, including both flagellates and ciliates. I have been looking at agricultural soil samples under the microscope for two years now, and this kind of result is consistent with almost every field we have sampled from.

Going back to the original post, which showed¬†these two jars next to each other…

IMG_3700

… I think we now have a better idea of why one was so clear and the other was so cloudy. The field soil is full of tiny particles and vast populations of bacteria, whereas the garden soil had more structured¬†soil with greater biodiversity.

So what does this mean for plant growth?

Here was the result of a sprouting test using the two different soils. Without looking at the labels, can you guess which one was which?

Sprouting test, using cress seeds.

Sprouting test, using cress seeds.

You probably figured out that the left is the garden soil. Even a hardy, fast sprouting plant like cress struggled to survive at all, but flourished in the garden soil. Why might this be?

An even better question: why is a farm producing soil like this, and why is this considered normal?