Closing the Loop

Like most people, I once spent virtually no time thinking about the content of toilets and where those contents went after a flush. This all changed when I began my Ph.D. work in Dr. Deirdre Griffin LaHue’s Soil Health Lab at Washington State University. With funding from the FFAR Fellows Program and the King County Wastewater Treatment Division, my graduate research focuses on how biosolid byproducts from our waste stream can improve soil health and support sustainable agricultural production.

My research focuses on how biosolids influence the physical, biological, and chemical soil health properties of semi-arid dryland grain systems, and whether biosolids can help growers establish cover crops in these systems. The geography of this research is in dryland systems in Central Washington. These systems face some specific challenges related to water availability that can severely limit crop yields. Annual precipitation in this area is low (~10 inches of precipitation a year), and these systems rely solely on precipitation to meet the water needs of the crop (this means they are completely unirrigated).

One of the beneficial uses of biosolids is land application as nitrogen fertilizers. Land application is a way to close nutrient cycles by redistributing nutrients and organic matter in human waste from densely populated areas where more food is consumed back into the often less populated agricultural areas where more food is produced. This allows the nutrients being taken out of agricultural landscapes to be replaced.

Biosolids are not only a source of nitrogen for crops, they also contain other plant essential macro and micronutrients and are high in organic matter. Increased organic matter levels in the soil have been shown to improve important soil physical properties like aggregation, water infiltration, and water retention. Organic matter inputs can also increase soil carbon levels and stimulate biological activity. All of these biosolid benefits can improve soil health.

Due to the moisture limitation in these systems, many farmers in the area implement a crop-fallow rotation to conserve soil moisture and stabilize yields. While this practice is important to help maintain yield stability, it can leave the soil exposed for long periods of time, which can lower soil organic matter levels and increase erosion potential. With an increase in soil water holding capacity, farmers might be able to reduce the time fields are fallow which could allow for a more diverse rotation of crops on their farms. For example, at one of my research sites, we are working with a local farmer to explore whether biosolids applications can help farmers integrate cover crop grazing, allowing farmers to supplement cattle diets at low cost.

Something that really excites me about my research is that it addresses several important and pressing sustainability challenges for Washington state, from urban wastewater management to soil health and sustainable productivity in dryland agricultural systems. I have the opportunity to work within a framework that includes a variety of stakeholders who are putting our research into practice. In addition to monitoring soil health, I have met with farmers who participate in the research we are conducting in Central Washington and members of the King County Wastewater Treatment Division to present our research, discuss our research plans and get feedback on their interests and needs. I also get to work with Northwest Biosolids, an organization that provides additional research funding and an avenue for us to deliver education and technical assistance to its members, which include municipal wastewater treatment plants and regulating organizations. This has shown me just how far-reaching research impacts can be, and how valuable it is to work with stakeholders from different backgrounds when conducting research.

My participation in the FFAR fellows program has allowed me to dig even deeper into this rich experience, by giving me the opportunity to develop skills that relate to science communication, project management, and organization. The FFAR fellowship has also given me the opportunity to work with mentors who can provide more personalized guidance in relevant areas outside of my research focus. I feel that this experience has allowed me to be more confident in my interactions with stakeholders from different disciplines.

Watch Madeline’s 2024 third-place ‘Lightning Talk’ where she discusses her research. The annual FFAR Fellows Lightning Talk Competition is a way for fellows to create and practice their science communication skills in a supportive peer-mentorship environment, and then share their talks with the public.