Grassland resilience through biosolid compost amendments: Supporting soil health for improved agricultural community adaptation and climate mitigation

Alexia Cooper, School of Environment and Sustainability, Western Colorado University, Gunnison, CO, Jennie DeMarco, School for Environment and Sustainability, Western Colorado University, Gunnison, CO and Eric McPhail, Agricultural Extension, Colorado State University, Gunnison, CO

Background/Question/Methods
Land management of grasslands can play an important role in climate change mitigation by influencing soil carbon (C) storage. Soil amendments, such as adding compost, have been shown to increase soil C storage while simultaneously increasing plant productivity and soil water holding capacity (WHC), factors that provide immediate benefits to ranchers. Research to date has mainly focused on temperate annual grasslands little is known if irrigated perennial pasturelands in cold and arid climates respond similarly . Our objective was to determine the effect an application of five cm of locally sourced biosolid compost has on plant productivity, soil moisture, and C storage. Research sites were set up at four ranches in Gunnison, CO, a high elevation arid region. Within each site, two treatments (control and compost addition) were established with five replicate plots within each treatment. Throughout the growing season, we measured soil moisture every week. In the fall of 2019, above-ground plant biomass was harvested. Soil samples from 0-10 cm depths were collected to measure soil organic matter (SOM), C:N ratios, C pools, and other soil health properties.
Results/Conclusions
During the first year, compost treatment increased total biomass on average by 66% (SE ± 18) across sites (F3,32 = 62.3, p < 0.001). Soil moisture increased in the treatment plots relative to control and was significant at two of the four sites (F1,1251 = 54.5, p < 0.001). Percent SOM was highly variable across sites, and did not significantly change with compost treatment. The absolute change in %SOM within sites control and treatment was 4.6% (SE ± 2.37). The C pool sizes (C g/m2) across the sites had a trend of increased C but was not significant within sites. The average increase between C pool size concentration of treatment relative to control within sites was 37% (SE ± 21). Our study demonstrated that a single application of biosolid compost can elicit a significant increase in soil moisture throughout the growing season and stimulate an increase in the production of biomass. Compost amendments can decrease the risk of ranchers to drought while fostering increase C storage. These are short term responses, and we are unsure of what the long-term responses will be.