Author: Sarah Abigail IsbellPublisher:
ISBN:
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Languages : en
Pages : 0
Book Description
This dissertation explores strategies for ecological intensification of agricultural systems through interactions of crops, soil, and the soil microbiome. I evaluate the impacts of these interactions on nitrogen (N) cycling--an ecosystem service that can be observed at an agroecosystem scale but has impacts on a global scale. Both plant communities and soil microbial communities are key drivers of N cycling in terrestrial ecosystems. This dissertation investigates connections between these communities using the agricultural practice of cover cropping as a model to explore this aboveground-belowground connection. My research builds scientific knowledge with direct links to agricultural sustainability: the reduction of environmental and health risks associated with N leaching into the water supply, the improvement of economic productivity for farmers, and the conservation of soil and protection of natural resources. My first experimental chapter (Chapter 2) evaluates N dynamics in organic grain cropping systems that integrate multiple ecologically based management strategies. In this experiment, four agricultural management systems were compared. These management systems varied in soil tillage strategies, CC species selection, CC termination and establishment methods, fertilizer management, and grain crop season length. I used field measurements to investigate the impact of each system on N in soils and in crop biomass, and to reveal the strengths and weaknesses of each system in addressing N provisioning services. The clear takeaway that emerged from this experiment was the importance of targeting synchrony of soil N availability with crop N demand--in other words, managing all components of the system to ensure that there is N in the soil available for uptake by the crop at the time when the crop needs the most N. This synchrony is influenced by the capacity of CCs to retain N and the timing of N becoming available to the crop as driven by soil tillage. My third dissertation chapter focuses-in on one agronomic practice that was included in the systems experiment described above. I designed a targeted experiment to test CC interseeding as a strategy to reduce N leaching in organic corn production. In the Northeast, short and increasingly unpredictable fall and spring seasons can cause problems with establishing a CC following corn harvest, an issue identified both in the scientific literature and by farmers (Ketterings et al. 2015). Interseeding CCs directly into growing cash crops has gained interest as a strategy to address this constraint (Groff 2015). To my knowledge, this study is the first to directly evaluate the effects of interseeding CCs on the potential to decrease residual soil N and therefore decrease N leaching in an organic system. Takeaways from this experiment include the following: 1) both the standard CC regime and the practice of interseeding CCs had a similar capacity for N retention and reduced N leaching, showing that interseeding CCs is a viable option for promoting N services; 2) reduced N leaching was driven by N storage in CC biomass, indicating the importance of CC species selection for N retention; and 3) total soil microbial biomass and taxonomic composition was similar among all CC strategies, suggesting that microbial dynamics were not closely linked with the CC treatment, but instead driven by other inputs in the system. In my last research chapter, I strive to understand how CC species mixtures engineer the soil microbiome. Plant roots strongly impact microbiomes in the soil through the secretion of root exudates (Chaparro et al. 2012), and this impact varies by plant species (Turner et al. 2013). Specifically, this work builds knowledge about the impacts of specific CC species and mixtures on belowground community structure and functioning, which serves as a building block for advising growers on soil microbial management. I found that different CC species do drive differences in the associated soil microbiome, and that the soil microbiome engineered by mixtures is not "additive" based on the component monoculture soil microbiomes. I found evidence to support my hypothesis that there were antagonistic and/or synergistic interactions taking place within mixtures that impacted soil microbial communities, as well as evidence that microbial recruitment from plants in mixtures is environment dependent. These results provide a foundation for further research into manageable regulation of soil microbiomes through leveraging plant-microbe links, with potential for agronomic, economic, and environmental consequences. There are still many barriers to adoption of ecologically-based management strategies, including reduced-tillage systems, interseeded CCs, and the use of CC mixtures. While some of these barriers can be overcome through continued scientific research to further our mechanistic understanding of these practices, many of the barriers are economic, structural, political, and cultural. It will require collaborative efforts from research institutions, policymakers, extension services, industry partners, and farmers to overcome these challenges and contribute to creating environmentally sustainable, resilient, and just agricultural systems.