Here at the UW Farm, we make our own compost, combining different types of dead plant material and animal manure to create just the right ratio of Carbon to Nitrogen needed for effective composting. Temperature is used to monitor the composting process, and the compost pile gets turned every so often to add oxygen and keep things running. The finished product is the fully decomposed, nutrient-rich compost that both plants and farmers love. Sounds pretty simple, right? In reality, the composting process is actually incredibly complicated, involving billions of tiny organisms with various metabolisms and ecosystem functions, all working together to create our compost. Fortunately for us farmers, all we have to do mostly, is just sit back and let the microbes do the dirty work! But for my BIOL 399 internship project, I wanted to understand a bit more about the microbiology and science behind the composting process.

When working on my project, I did some background research on different aspects of the composting process, and learned a ton about the chemistry and microbial ecology of compost, as well as various ways to monitor the process. To test out some of the things I learned, I examined four of the compost piles we have going at the CUH, each in a different stage of the compost process. Two of the compost piles were in the later maturation phase (1 and 2), one was just about to enter the thermophilc (when the compost temperature is highest) phase (5/6), and the other was in the middle of the thermophilic phase (C). Over the course of the quarter I measured the temperature and pH of each pile on a weekly basis, and tested out other methods to investigate the microbe and insect communities.

Here are some of the highlights of what I discovered and learned this quarter:

– Temperature is not the only way of monitoring the compost process. Each of the three phases of the process (initial mesophilic phase, thermophilic phase, and maturation phase) differs from the others in pH and microbial community structure.

– Nematodes, in particular, are a cool way of determining what phase of the composting process a pile is in.  The nematodes found in compost are generally of either the bacterivorous or the fungivorous variety, which can be determined by examining features of their “mouth”. In the thermophilic stage, bacterivorous nematodes dominate, while fungivorous nematodes are more likely found in maturing compost.

– The chemical and microbial properties of compost can vary significantly within a single pile, especially when comparing the outside edges to the center. This is important to consider when doing experiments involving compost samples with multiple replicates from the same pile- it makes determining statistical significance difficult (see ginormous error bars in data below).

At the end of the quarter, I compiled all of the research that I did on compost into a PDF file, that can hopefully be used by future UW farmers to better understand the compost process and plan other projects for internships and even outreach efforts. There are still a lot other experiments and assays that I had hoped to try, but wasn’t able to accomplish within the timespan of a single quarter. Despite this, I definitely still enjoyed my internship experience, and it was a great way to spend my final quarter at UW!