Abstract
Soil health relates to the ability of soils to sustain ecological functioning, productivity and quality in both natural and agricultural ecosystems. Regenerative agriculture management seeks to promote soil health through practices that positively influence physical, chemical and biological properties of soil. In this thesis, we look to expand both how we define and measure soil health, and we explore the role of regenerative agriculture in contributing to more healthy soils. Soil microorganisms represent an important source of ecosystem services within soils, thus, understanding how soil microbial communities respond to environmental stress is essential when making dynamic estimates of soil health. For a dynamic approach to measuring soil health, we quantified microbial stability—resistance (RS) and resilience (RL) to stress—based on several response variables including mass-specific respiration, enzyme activity and decomposition. We drew comparisons of microbial stability between two agricultural management regimes: conventional and regenerative systems. Surprisingly, microbial RS and RL were negatively correlated with each other. This divergence suggests a tradeoff in microbial life strategies taken both during and after experiencing stress. Conventionally managed soils exhibited marginally higher RS, while regenerative soils had greater RL to applied temperature and moisture stress. Traditional soil health metrics (e.g., permanganate oxidizable carbon, soil respiration, microbial active C) correlated well with soil RL but not with RS measures, indicating these tests may provide useful (but limited) proxies for dynamic estimates of soil health.
We also investigated a specific regenerative management practice—compost amendments—to better understand optimal strategies for application. We tested the effects of seasonal timing of compost additions on multiple soil parameters in a field experiment in Pullman, WA, USA. We found no effect of the seasonal timing of compost application on soil parameters within the one-year experimental term. In general, compost additions had little effect on measured soil biogeochemical properties and crop yield. However, emerging trends in our results suggest there may be value in regular compost amendments beyond the one-year term analyzed in our study. In conclusion, there is still much to be learned regarding the potential of regenerative agriculture, though we were able to demonstrate benefits to soil health provided by regenerative agricultural management in the form of increased environmental resilience.