Recipient Organization
APPALACHIAN STATE UNIVERSITY
(N/A)
BOONE,NC 28608
Performing Department
(N/A)
Non Technical Summary
Compost amendments are an increasingly popular rangeland management strategy to increase both soil carbon and forage production. A positive effect of compost on soil carbon has been attributed to direct carbon inputs as well as indirect inputs from resource-stimulated plant growth. However, there is considerable variation in rangeland soil carbon storage after compost amendment. Soil biotic communities may account for this variation. Soil communities alter soil carbon directly through decomposition and indirectly by affecting plant productivity (via both nutrient availability and root predation). Compost is widely used in croplands to shift soil communities away from parasites and toward beneficial taxa, but these effects may vary in rangeland systems as they experience greater environmental variability over space and time.The premise of our research is that soil communities are key mediators between rangeland compost amendments and soil carbon storage. Taking a soil ecology approach, we propose: 1) a spatial survey of soil community composition across 15 compost-amended sites in California spanning climate and edaphic gradients; 2) a temporal survey to assess how soil communities shift with carbon pools across a compost amendment chronosequence; and 3) an expanded soil carbon model that explicitly accounts for microbial C pools and an experimental test of the relative inputs from plants and invertebrates to soil carbon in amended versus non-amended soils. Our results will contextualize the mechanisms and conditions under which compost amendents increase soil carbon storage, and our outreach will help stakeholders decide when and where to apply amendments to optimize rangeland soil health.
Animal Health Component
80%
Research Effort Categories
Basic
15%
Applied
80%
Developmental
5%
Goals / Objectives
Compost amendments are an increasingly popular rangeland management strategy to increase both soil carbon and forage production.The premise of our research is that soil communities are key mediators between rangeland compost amendments and soil carbon storage.Our overall goal is to contextualize the mechanisms and conditions under which compost amendments increase soil carbon storage.Taking a soil ecology approach, our objectives are to:1)Assess how compost amendments affect rangeland soil communities.Studies have shown that increasing soil organic matter boosts abundance of beneficial soil organisms and reduces pests. In croplands, managers have taken advantage of these benefits and applied compost as an alternative to chemicals for pest management. However, less is known about the effects of compost amendments on rangeland soil communities where edaphic and climatic factors are highly variable. We hypothesize that compost amendments will enhance beneficial soil organisms, but the magnitude of these effects may depend on environment.2)Assess how soil communities change over time in compost-amended soils.Soil communities shift over time both as the soil environment changes and C substrates decompose and change forms. We hypothesize that compost will have immediate and lag effects on soil communities, and which taxa respond will correlate to decomposition patterns as soil OM pools shift over time.3)Understand the consequences of soil community responses on ecosystem C storage.Soil C dynamics change over time as OM decomposes, improving soil aggregation and increasing the capacity for soil to store C in stable, physically protected pools. The timing of these changes depends on environmental factors such as precipitation and soil texture. While compost generally increases soil C, this pattern is not universal and likely depends on environmental context and soil community response. We hypothesize that the strongest positive effect of compost amendments on soil C will occur in environments in which amendments most greatly increase beneficial soil biota.
Project Methods
SPATIAL SURVEY: We plan aspatial survey across 15 compost-amended rangelands in California to test the effects of compost on soil communities across climatic and edaphic gradients. We capitalize on an extensive network of existing amendment experiments (sponsored by the USDA as well as the state of California)that span a range of mean annual precipitation (MAP) to test spatial variability in the response of communities to compost amendments.Here, weconcentrate on the effect of compost amendments on the soil community. We will analyze soil organic carbon content, soil nitrogen availability, and soil communities from paired unamended and compost-amended plots at each site. This observational approach will allow us to assess the effect of compost applications on soil communities in relation to climatic and edaphic variables.TEMPORAL SURVEY: To test temporal variability in the response of communities to compost amendments,we focus on two sites with compost amendments applied in multiple starting years to assess the temporal dynamics of soil communities and soil C in amended rangelands. Here, we concentrate on two of our survey sites - Marin and Yuba County - which were the focus of some of the earliest compost amendment studies conducted by the Marin Carbon Project and have also been used as sites for more recent amendment experiments. We will pair existing amendments with new compost addition and control plots to capture compost effects from 0 to 15 years. This will allow us to specifically examine the temporal effects of compost addition by comparing soil communities in fresh versus older additions (i.e., 0, 5, 7, and 15 years since compost addition) versus control plots and then explicitly testthe relationship between community composition and soil C pools. Marin County is coastal grassland that experiences higher rainfall than valley grasslands in Yuba County, allowing us to also compare climatic effects. SOIL CARBON MODELING:We extend models of soil C dynamics to explicitly include microbial pools. Here,we willlink the chemistry of compost inputs with the efficiency of microbial processing and soil organic matterformation and stabilization using theMicrobial Efficiency-Matrix Stabilization (MEMS) model (i.e., Robertson et al 2018).Webuild on our soil C fractionations and microbial biomass measurements from the new compost addition plots in the temporal survey in H2 (described in section 3.2) and will also includesoil respiration and compost C fractionations to parameterize the MEMS model. Using the MEMS framework will allow us to better understand C storage in the context of microbial processing under compost amendments. We will use the model to project long term C storage for our new compost addition plots at the two sites and compare different C pools projected by the model for to actual C pool measurements from the plots of 5, 7, and 15years old at the same sites.INVERTEBRATE ROLE IN SOIL C: We will experimentally test the pathways by which soil invertebrates affect soil C in a factorial experiment that crosses compost amendment, invertebrate presence and plant presence. This will allow us to differentiate the direct effect of soil communities on soil C via decomposition versus the indirect effect via plant growth.This framework will allow us to compare the abiotic effect of compost (with or without amendments in the absence of plants and invertebrates) to the direct effect of invertebrates (with or withoutamendments × with or without invertebrates in the absence of plants) to the effect of invertebrates mediated by plants (all three).Within the new compost addition plots, in Year 2 we will exclude plants and invertebrates in a factorial design to determine the relative contribution of each to soil C storage. Invertebrates will be excluded using chemical fumigants shown to have minimal effects on soil C and microbes. Plants will be excluded by hydropulverizing seedlings in the fall following germinating rains. This technique allows plant removal with minimal soil disturbance and is highly effective in small plots such as ours. We will conduct the experiment for one year collecting environmental, plant, and invertebrate data.Annual milestones include: Year 1 - compost applied for temporal survey (fall 2024), spatial survey completed (spring/summer 2025), first year samples collected for temportal survey (spring/summer 2025), spatial/temporal survey soil samples processed for abiotic (C, OM, N), and biotic (microbial) data (summer 2025);Outreach compost and rangeland webinar (summer 2025)Year 2 - temporal survey maintained (fall 2025), experimental treatments initiated(fall 2025); model parameterized/run (fall/winter 2025), and second year samples collected for temportal survey and experiment samples collected (spring/summer 2026), samples processed for abiotic and biotic data (summer 2026), manuscripts drafted and spatial survey results and model results presented at conferences (summer 2026);Outreach compost and rangeland webinar (summer 2026)Year 3 - Presentations at rancher/scientist field day (fall 2026),experimental data analyzed and manuscript drafted (fall 2026), final data measured for temporal survey (spring 2027), temporal data analyzed and manuscript drafted(summer 2027), temporal survey and experimental results presented at conferences (summer 2027);Outreach compost and rangeland webinar (summer 2027)