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.
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.
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.
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.