Only 2,548 samples to go…

Funnels and filter ready to go.

At the AgroEcology lab, I primarily work with Josh Gaimaro on his research pertaining to cover crop use as a best management practice. Within my first two weeks of working in the lab, I was introduced to potassium chloride (KCl) extractions, which are one of the central procedures to his project. KCl extractions allow us to quantify the nitrogen concentration in soils, which helps model how the nitrogen moves through the soil, and how much of it gets taken up by plants or leached. Over the past two years, Josh collected over 1,000 samples, all which needed to be organized, weighed out, and extracted. Additionally, each sample required a replicate for quality control, which doubled the extraction count. When I was first introduced to the procedure, I did not understand the sheer quantity of samples I would need to process...

The first KCl extraction wasn’t perfect, even though Josh made the entire process look quick and effortless at first glance. The procedure is as follows: After weighing out a set of soil samples, we calibrated a pipette to dispense KCl into each tube. Afterwards, these samples are transferred to a shaker table, where they shake for an hour. In the meantime, you must prepare for the extraction which consists of setting up scintillation vials, placing funnels into them, and folding filter paper for each sample. Next, the tubes must go on a centrifuge to speed up filtering. However, we could only centrifuge 12 samples at a time, so it would take some time to get through all the samples. After the centrifuge, the samples are all filtered and organized once again.

Soil extractions!

The first extraction was around 75 samples, which wasn’t too intense since I was shadowing Josh and he was leading the procedure. Everything ran smoothly until the very end, where we were pouring the samples into the vials. We were using a shaky wooden device, which held the funnels a little above the vials, but didn’t secure the vials from moving. As I was pouring a sample, I accidentally knocked one over and it caused a domino effect! Three samples went down, and I was utterly embarrassed. Josh assured me that it is no big deal, and that we will redo these samples another day. Little did I know, I would do an extraction just like this at least twice a week at the minimum throughout the entire summer. The following day I was asked if I could do an extraction by myself with the help of another intern. Without giving it much thought, I replied “sure”, and began my journey of KCl extractions.
Once I got into the groove of things and familiarized myself with the procedure, I was averaging at 300 KCl extractions per day. This included the entire process- starting with weighing all the samples to cleaning up all of the dirty funnels and tubes. Little by little, I started working through these samples until the number of extractions left to do was zero. At first, the process didn’t seem to have an end, but somehow after three months of work, we finally finished the samples. Our last extraction was last Thursday, and was definitely bittersweet.

References:
Jones, D.L, Willett, VB. (2006) Experimental evaluation of methods to quantify dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) in soil. Soil Biology and Biochemistry, 38:5: 991-999 https://doi.org/10.1016/j.soilbio.2005.08.012.
Murphy, D., Macdonald, A., Stockdale, E. et al. (2000) Biol Fertil Soils 30: 374. https://doi.org/10.1007/s003740050018