Composted biosolids amendments for enhanced soil organic carbon and water storage in perennial pastures in Colorado

Abstract

Land management of grasslands can play a significant 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. However, little is known if irrigated perennial pasturelands in cold, arid climates respond similarly. This study’s objective was to determine the immediate effects of a 5 cm depth application of biosolids compost on plant productivity, soil moisture, and soil C storage. Research sites were established at four ranches in Gunnison, CO, a high-elevation, arid region. During the first year, there was a significant increase in total aboveground biomass (AGB) across three of the four sites (F3,32 = 62.3, p < 0.001), resulting in a difference in total AGB of 199.83 g·m−2 (95% CI 133.6 – 266.1 g·m−2) between the control and treatment, an average increase of 109% (SE ± 20%). There was a significant increase in soil moisture in the treatment plots relative to the controls at each site for most of the growing season (July-Oct). On average, soil organic matter (SOM) increased by 32% SE ± 10.5, with two sites demonstrating a significant increase. Soil C stocks increased across sites with biosolids, but this was only significant at one site (F1,32 = 7.05, p = 0.012), the most degraded of all four pasturelands. This study demonstrated that a single application of biosolids compost could elicit a significant increase in soil moisture throughout the growing season and increase plant biomass production. Biosolid applications can also increase SOC. However, this response's magnitude is site-specific and is associated with the degree of soil degradation, which might be related to land management history. Using biosolids compost on pasturelands seems to be a positive strategy to improve soil health and its associated co-benefits. Still, managers should consider the degree of degradation of their land when determining cost benefits.