Case Study by CART

Both in theory and according to existing research, compost application can in many cases be beneficial to rangelands ( Kutos et al. 2023 ). However, finding the most efficient deployment methods are key for scaling. For example, strategic placement according to local conditions and management systems or finding the best kind of compost for a given landscape may lead to more beneficial outcomes at a lower cost to producers. Little is known about the optimal conditions for applying compost in diverse landscapes and under various management systems. As a result, many potential benefits of composting for ranchers remain untapped.

A wide range of compost types are available to producers, but little is known about the effects of different types of compost on specific plant and soil health attributes. Two of the more accessible options are biosolid-based compost, made from municipal sewage, and manure-based compost, made from livestock manure. Both types of compost are relatively affordable and support a broader circular economy principle, showcasing the potential benefits of using waste materials to restore semi-arid rangelands. 

• Measure the ecological benefits of applying biosolid-based compared to manure-based compost to rangeland over time, by monitoring soil, plant, and microbial community responses six months and one year after compost application in study plots.
• Offer information and advice, rather than prescriptive guidelines, that can help inform producer decisions about how to apply compost to their land and which type to choose.

Image Caption: Collecting a soil subsample in a control plot to measure soil organic carbon at a small in-field demonstration workshop. Courtesy of Eva Stricker, University of New Mexico.

• Experiments in the Field: The research team studied nine 64 m2 loam soil plots with <5% slope on privately-owned rangeland in New Mexico. Each plot was randomly assigned to one of three treatments, with three replicates each: an addition of manure-based compost, biosolid-based compost, or no compost to the soil surface. The team visited these plots both at six months and one year post-treatment to collect soil health and vegetation data.
• Compost Type Affected Plant Performance: Six months after treatment, vegetation in plots that received biosolid-based compost had grown the most, with a non-significant trend of over double the amount of plant biomass than in plots with no compost. Vegetation in plots that received manure-based compost showed intermediate levels of plant growth compared to untreated plots. 
• Soil Characteristics Changed Over Time: Aggregate stability, an indicator of soil health and quality, initially decreased at six months. This may have been a result of increased livestock movement, trodding on the compost plots. After one year, aggregate stability in plots with manure-based compost recovered to native soil stability values, and increased at intermediate levels in plots with biosolid-based compost as well. 
• Resilient Native Soils: Both compost types host diverse communities of fungi and bacteria. Researchers therefore expected large changes in microbial diversity in plots with compost additions. However, they found that six months and one year after treatment, microbial communities in native soils in all plots did not shift dramatically. This surprising result indicates that microbial ecosystems in native soils are well-established and not destabilized by new microbes from compost. In practice, this suggests that while compost improved some soil health metrics, the dominant microbes were not primarily responsible for observed changes in soil or plant responses.

Image Caption: Setting up a livestock exclosure on a new compost addition plot. Courtesy of Eva Stricker, University of New Mexico.

Despite varied results between compost types and at different time intervals, compost additions overall increased plant growth and improved some soil properties. At this stage in the research, one compost type has not proven to be dramatically more effective than the other. These mixed preliminary results indicate that compost shows some promise as a tool to increase rangeland productivity. Importantly, they also highlight the importance of continued research on the ecological effects of compost. By quantifying the potential ecological benefits of compost, researchers can help producers to make a more informed decision about investing time and money into this practice.

This study demonstrates one way in which waste can be used productively on rangelands, contributing to a broader rangeland circular economy. The research team hopes in the long-term, their findings can help shift producers’ perspective on waste towards increased strategic use. Here they show that, for example, composted excess manure from dairy cows could be beneficial for soil health. Ultimately, the research team aims to integrate waste transformation into improved ecological, social, and economic outcomes for rangeland producers. This mindset change is one important step towards regenerative management.

Image Caption: Drone image of compost plots in spring 2021. Courtesy of Eva Stricker, University of New Mexico.

• Continue this line of research: When currently funded components of the project conclude in 2024, researchers will have collected two years of data; this slightly longer time scale will help researchers investigate whether or not the benefits of compost vary over time.

• Conduct additional experiments in summer 2023 to study how far microbes travel from the plots where compost is added: Understanding the microbes’ dispersal capability from the application of compost will help researchers make recommendations on optimizing compost placement and amount needed to see benefits.

• Initiate further research on if compost will build resistance or resilience to drought.

• Collaborate with economic experts to conduct cost analyses of using compost: Once researchers have a clearer understanding of the ecological benefits of compost, they hope to incorporate both ecological and economic context to present the cost-benefit ratio of compost to producers. They recognize that compost is an expensive tool, but that the benefits may outweigh the cost. The research team aims to consider the net outcome of using compost for producers, not just the absolute cost.

Image Caption: A compost plot during the monsoon season. Courtesy of Eva Stricker, University of New Mexico.