CHAPTER 8: A Summer of Lab-work

Field by day; garage by night. In six words, that was pretty much my summer, and I wouldn't have had it any other way. Whilst the days were spent out (quite literally) 'in the field', I would usually be found in the garage during the evenings, working on my samples.

I always knew that with a project such as this, I would need some sort of makeshift laboratory, so I get some of lab-work out of the way before heading back to university. On June 24th, Dad and I set out and gutted the garage; it was one of the very few times that I've seen it with absolutely nothing in. And whilst it was great to give it a tidy, my main objective was to re-arrange it so that we could fit a couple of tables, thus providing me ample space to do the necessary work.

What was this work? Largely it consisted of a lot of soil drying, and for this, I used a small but pretty powerful microwave. Drying a soil is important, perhaps for two reasons. If one weighs a sample of soil before and after drying, the difference between the two measurements is the water content. Knowing the water content of the soil is extremely vital, as water drives many of the processes within the soil system. If a soil has too much water (we call this saturation), then upon the next rainfall event, precipitated water will more than likely runoff the surface rather than infiltrating through. If a soil, on the other hand, has rather low moisture contents, then the system is more likely to allow some of that rainwater to infiltrate. The second reason why drying a soil is important is perhaps best explained by considering a batch of samples that haven't been dried. There's one test called the Aggregate Stability Test, and this basically tests how soil aggregates behave when they are repeatedly immersed in water. It's supposed to simulate what happens during a rainfall event; after all, when it rains, soil particles receive the rainwater in the form of intermittent droplets, with a gap (albeit seconds) where the soil isn't receiving water. Anyway, if the test is trying to understand how different soils behave, everything else must remain constant. These constants include, for example, the temperature of the water, the rate at which they are immersed, but it also means that the water content within the samples has to be constant. Therefore, samples are dried so that the scientist can safely assume that each sample has a constant (zero) water content. Water, incidentally, can bind particles of soil together (we call this capillary action) and it actually increases their stability!

Part of my laboratory work would also take place at the Royal Holloway. By placing samples in a furnace and heating them to about 550 degrees C, you effectively burn off the organic matter. Similarly, by weighing the samples before and after this process, one can calculate how much organic matter there was within the sample. My crop roots would release organic matter into the soil, and I was interested in seeing the effect of root tapering on this. Would larger surface areas of root, for instance, release more organic matter into the soil? Another test I completed at the university was one that had never been done here before, and that was to quantify the volume of soil polysaccharides within the samples. Polysaccharides are basically carbohydrates, which are often released by roots. To put a very complicated method simply, the polysaccharides within my soil samples were removed using various chemicals and placed in a machine called a spectrophotometer. This little machine measures how easy light travels through a solution. (For instance, if you were to measure milk, the transmittance of light would be fairly low, in comparison to, say, clear water). One by one, each of my samples were placed through and measured. And then, I did the same for a selection of 'known glucose standards'. In other words, I could work out the light transmittance for various solutions of known polysaccharide content. These could then help me to create a graph - a glucose curve - with polysaccharide content on the horizontal axis, and light transmittance on the vertical axis. All I would need to do then is to take the light transmittance of one of my soil samples, find its position on the curve, and look down to see its polysaccharide content. It sounds technical, but after you've done one, it's a case of repeating the method. By the end, I could have probably done it in my sleep!


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