My Experience in Forestry: The Soil Lab

Megan Young, Adopt-A-Pond’s Wildlife Biologist, took part in an internship in Sault Ste Marie, Ontario, at the Great Lakes Forestry Centre for 12 weeks over the winter. She was working as a First Nations Intern with the Forest Ecosystem Research and Assessment Team within the Canadian Forestry Service/Natural Resources Canada. As she learned a lot about the soil and plant ecology side of the forest ecosystem, she’ll be sharing some aspects of what she’s learning on our blog! Check back for updates from her experience. 

Blog 1: The Soil Lab

My first placement at my new internship was in the Soil Lab. I was helping to measure soil moisture content, analyze soil nitrogen and carbon content, and determine soil textures. Although I know that these are all important factors relating to soil productivity, some of which we try to quantify during Adopt-A-Pond’s fieldwork, I didn’t know a lot about the soil ecosystem or about how to quantify these variables. 

In the soil lab, my most fun (and noisiest) job was determining  soil texture. Soil is divided into two separate types: organic or mineral soil. Organic soil has more organic matter content and is closer to the surface, whereas mineral soil has little to no organic matter and is usually deeper. When measuring soil texture, one only considers the mineral soil, which is made up of particles less than 2 mm in size. There are three major groups of particles: sand, which is the largest, silt, and clay, which is the smallest. Soil texture is determined by the proportion of each of these different particle sizes. 

MVIMG_20191218_131024
An example demonstrating the different sizes of soil particles and the different percentages that make up a soil.

There are a number of methods that can be used to determine the soil texture type, but the method I used was the hydrometer method. Before the texture can be determined, the soil samples have to be ground, and sieved, and then mixed with a soil blender to remove the organic matter so that only clay, silt, and sand are left and any large clumps are broken up. The samples are then suspended in a solution and mixed thoroughly to make sure that no particles have sunk to the bottom, kind of like a soil/water milkshake.

mixsoil

After mixing, a hydrometer is put in the solution at different time intervals and a reading is taken. A hydrometer is an instrument that essentially measures the amount of particles in suspension (i.e. not sunk to the bottom) – the higher the number, the greater the suspension density or the number of particles, and so the higher the hydrometer will float in the liquid. The difference in particle size means that the particles will sink at different rates, so at different time intervals since mixing, there will be one, two, or all three particle types in suspension. The density of the solution at these time intervals is used to calculate the percentage of sand, silt, or clay in the sample. Sand is the largest and so sinks incredibly quickly. To get a measurement for how much sand is in the sample, you have to put the hydrometer in the solution almost immediately after mixing. It has to stop bobbing within 45 seconds so that you can get a reading! The next measurement is for silt at 2 hours and then for clay, at 24 hours later. So these soil texture determinations take at least 2 days of planning and coordination to make sure you’re taking the hydrometer measurements at the right time. 

MVIMG_20191218_131015
A series of soil samples that are ready to be measured for texture.

Soil texture can tell you a lot about the other properties of the soil, like its capacity for holding water or nutrients. For example, clay soils have a higher capacity for water retention whereas sandy soils have larger spaces between the particles and so water can drain more quickly.  I was really interested in measuring soil texture because soil texture is incredibly important to turtles when they’re nesting. They can be picky about where they make their nest and much of that depends on the soil! 

In the Soil Lab I had to review a lot of physics and some chemistry to make sense of everything I was learning. There were electrical charges, oxidation, gradients, buoyancy, and drag, just to name a few. My second placement was with the Microbial Ecology lab, so I’ll use more chemistry and ecology next!

For more information about soil science and the Great Lakes Forestry Centre, please check out this cool news story!

nrcs142p2_050619

The soil texture triangle provided by the USDA. Once you know the makeup of the soil based on the three percentages of sand, silt, and clay, you can use the triangle to determine the soil type.