Dissertation
Quantifying soil nitrogen transformations at microbial, site-specific and field scales: A comparison of modified and established methodologies
Doctor of Philosophy (PhD), Washington State University
01/2016
Handle:
https://hdl.handle.net/2376/112664
Abstract
Microbial conversion of soil organic matter (SOM) to plant available forms via N mineralization (Nmin) can account for up to 100 % of the nitrogen (N) fertility of non-legume crops, yet the difficulty of quantifying this contribution prevents incorporation of accurate SOM credits into fertilizer recommendations. Enhancing our ability to quantify the N supplying capacity of agricultural soils requires a process level understanding of the environmental and biotic controls on Nmin across heterogeneous landscapes. This study quantified in situ rates of ammonium and nitrate production at multiple soil depths and landscape positions using a modified soil resin core (SRC) technique and compared these results to additional field and laboratory estimates to assess regional in situ net mineralization across dryland cropping systems of the Pacific Northwest (PNW).
In-depth accounting of nitrate and ammonium production and flux was possible via a six bag mixed-bed ion exchange resin system. Undisturbed soil cores (7.5 cm diameter by 15 cm deep) were isolated from the surrounding soil by three resin bags sealed in the top and bottom of individual plastic cylinders. NH4+-N was the dominant form of inorganic N extracted from resin bags recovered from fertilized and unfertilized locations, representing over 70 % of total resin inorganic N. Net mineralization estimates calculated using SRCs were sensitive to climatic and management conditions and values generated were comparable to other in situ methods, despite weak or insignificant relationships between in situ Nmin, yield, and laboratory measures of potential Nmin. Data synthesized from across the PNW suggests that regional estimates of a 2 % turnover of total N (TN) from the top 15 cm of the soil profile are informative as an Nmin proxy over a spring growing season, though larger turnover of TN can be expected if quantifying Nmin on an annual basis.
Additionally, a pressure cycling protocol was optimized to enhance the recovery of DNA from microbial communities that may be resistant to extraction using established methods. Results from this work indicate that extraction methods that recover the highest yields of total genomic DNA from soils may not recover the most diverse communities.
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Details
- Title
- Quantifying soil nitrogen transformations at microbial, site-specific and field scales: A comparison of modified and established methodologies
- Creators
- Emily Bruner
- Contributors
- David J Brown (Advisor)Lynne Carpenter-Boggs (Committee Member)Catherine Reardon (Committee Member)Erin Brooks (Committee Member)Richard Rupp (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Crop and Soil Sciences, Department of
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 93
- Identifiers
- 99900581724001842
- Language
- English
- Resource Type
- Dissertation