A quantitative evaluation of microbial interventions and biostimulant strategies in agricultural nitrogen management
Klimasmith, Isaac Mowry
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Permalink
https://hdl.handle.net/2142/124480
Description
Title
A quantitative evaluation of microbial interventions and biostimulant strategies in agricultural nitrogen management
Author(s)
Klimasmith, Isaac Mowry
Issue Date
2023-12-20
Director of Research (if dissertation) or Advisor (if thesis)
Kent, Angela D
Doctoral Committee Chair(s)
Margenot, Andrew J
Committee Member(s)
Below, Frederick E
Yang, Wendy
Ngumbi, Esther N
Department of Study
Natural Res & Env Sci
Discipline
Natural Res & Env Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Microbial ecology
biosimulant
nitrogen
agriculture
soil
Abstract
In response to the dual challenges of global population growth and environmental degradation, scientific and commercial focus on biostimulants as a possible route toward sustainable agricultural intensification has recently increased. In this dissertation, my work focuses on two types of biostimulants: nitrogen-fixing microbial inoculants and seaweed extracts. Microbial inoculants are applied to make diazotrophic bacteria more abundant in the soil, offering the tantalizing promise of maintaining crop productivity in the face of climate change while reducing dependence on synthetic fertilizers. Seaweed extracts are rich in carbon and micronutrients and can improve crop stress resistance, yield, and nutrient acquisition.
While both classes of biostimulants have the potential to interact with the carbon and nitrogen cycles within the soil, relatively little attention has been paid to the impact of biostimulants on soil microbial communities and the nitrogen transformations they facilitate. Understanding these dynamics is vital to sustainably deploying biostimulants, as prior studies have shown that some biostimulants can exacerbate agricultural nitrogen pollution.
The first three studies presented here quantify the impact of biostimulant addition on the microbial nitrogen cycle in maize agriculture. While seaweed extract addition appears to have little effect on microbial nitrogen cycling, nitrogen cycling outcomes under nitrogen-fixing inoculant addition shift depending on fertilizer application rate and in-furrow carbon addition. Overall, inoculant application alone can mildly exacerbate nitrification and denitrification in higher fertilizer conditions. However, these outcomes shift towards lower rates of nitrification and denitrification when the inoculant is paired with an intermediate fertilizer rate or in-furrow carbon. Across the growing season, the treatment effect of inoculant addition declines, suggesting that these bacteria struggle to survive and persist in the soil community.
To investigate practices that can improve inoculant persistence, I applied propagule pressure models developed for invasion ecology to microbial introductions. Based on inoculant persistence in a greenhouse study, these models predict that more frequent application (increased propagule number) but not increased inoculant concentration (propagule size) can raise the establishment probability of microbial inoculants. Together, these studies contribute to our understanding of biostimulants not as static inputs, but as interactive components of dynamic agroecosystems.
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