Compost-derived microbial dispersal in rangelands

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Commodities

• Additional Plants: native plants
• Animals: bovine, other

Practices

• Education and Training: technical assistance
• Soil Management: composting, soil microbiology

Western rangeland producers are faced with threats to their livelihoods as overgrazing has led to degraded soils and climate change-induced precipitation variability has made forage quantity difficult to predict. Sustainable management strategies are being promoted to ensure food system resilience and a healthy environment. Compost amendment is key to these strategies because of its ability to increase soil stability, water holding capacity, carbon and forage biomass. Because beneficial effects are observed even with small amounts of compost, microbial additions are likely pivotal to benefits because the novel community can potentially change the composition, function and plant/microbe relationships in native soil communities. These changes may extend beyond the compost application site but dispersal success and functional impacts of microbes have yet to be evaluated. This knowledge gap hinders producers’ ability to make informed decisions about optimal use of compost amendments.   

This study leverages existing field trials combined with DNA sequencing and established soil/forage assessment methods to identify successfully dispersing taxa, their functional traits and correlated effects on forage biomass and soil structure outside of the application site over time. Outcomes will inform producers about best application practices, possibly reducing the amount of compost needed and labor required to meet management goals. Results will be disseminated via field days, a webinar, a conference presentation and a paper. Data will be shared with RAMPS (Restoration Assessment and Monitoring Program for the Southwest) and RestoreNet, assisting land management agencies and producers in developing techniques for improving farming practices.   

 Research Objectives 

1. Determine how far bacterial and fungal components of compost-inoculated plots disperse to adjacent soils and how much bacterial and fungal biomass changes in adjacent soils. Investigate the traits of microbial taxa that preferentially disperse and their potential functional contributions to adjacent soils. 

1. Determine how transferred microbial communities affect plant biomass and soil structure. 

Education Objectives 

1. Based on the results of objectives A+B, provide technical support through education for interested producers. Engage the general public by sharing results in a fun and engaging manner at educational events.  

Ranchers manage waste products such as manure and thinned woody biomass and composting and amending soils can make productive use of this waste, mitigating detrimental environmental impacts that result from current disposal methods, thus improving the health and safety of the community. The benefits of compost addition to soil and plant health in rangeland systems have been well documented (1–6); however, research on the role of compost-associated microbes is in its infancy and there have been no studies investigating how far the microbial community and their effects on the environment will disperse. Investigation of the dispersal of compost microbes will address SARE’s goals of improving farmer and rancher quality of life and good stewardship of land by providing evidence on how far the beneficial effect of compost extends beyond the initial application area while still improving soil structure and plant health, potentially resulting in cost savings. Studies indicate that microbial diversity can promote plant community diversity, with microbes functioning in mutualistic or commensal relationships or as pathogens (7–9). Taxonomic classification of the community will identify known pathogens or beneficial microbes that will help determine potential impacts on forage species diversity. To assess the environmental implications of microbial dispersal, we will focus on soil structure and forage biomass, assessing the ability of microbes to combat soil degradation and increase forage yield.   

Research will be conducted at three sites in New Mexico across different elevations, soils, and climate (Table 1) to assess impacts across a broad set of southwestern rangeland conditions. Our proposed research leverages existing experimental sites that were inoculated with ¼” of compost in 2021 and 2022 allowing for study of microbial dispersal and function at agriculturally relevant time scales.   

Table 1. Abiotic and vegetation characteristics of the three ranches in New Mexico to be used to study microbial dispersal.