Nitrogen cycling and trade-offs with alternative manure application
Open Access
- Author:
- Duncan, Emily Wong
- Graduate Program:
- Soil Science
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 17, 2016
- Committee Members:
- Douglas Brian Beegle, Dissertation Advisor/Co-Advisor
Peter Kleinman, Committee Chair/Co-Chair
Curtis Dell, Committee Member
Jason Philip Kaye, Committee Member
James Hamlett, Outside Member - Keywords:
- Nitrogen
shallow disk injection
manure
field lysimeters
lysimetry
nutrient management - Abstract:
- Nitrogen management in agriculture remains an important challenge for today’s generation of scientists and producers. Many watersheds and regions struggle with excess nutrient management and the Chesapeake Bay watershed is not an exception. Few studies are able to encompass both environmental losses and agronomic measurements. The field lysimeter research location offers an opportunity to improve our understanding of management strategies. Every pathway of potential loss can be monitored on a replicated basis. The four chapters in this dissertation describe the unique site location, and the research projects that have added to our knowledge of dairy manure management. The first study (chapter 2) presents a hydrologic analysis of the research site—12 field scale lysimeters. Field lysimeters built at this scale are rare, and provide a unique opportunity to study environmental losses at a field scale as opposed to smaller column or pan lysimetry. However, the site is not uniform, and not all field lysimeters behave similarly. Based on hydrologic properties (volume and type of runoff), depth to bedrock, and hydrograph analysis, treatment-blocking maps were constructed to aid in future studies, and inform previously collected data. The second study (chapter 3) focused on comparing gas emissions (NH3 and N2O) associated with broadcast and shallow disk injection. Shallow disk injection significantly decreases ammonia volatilization compared to broadcast (surface) application of manure. However, the injection band from disk injection can increase N2O emissions, which is a potent GHG. Shallow disk injection of manure did double cumulative N2O emissions as compared to broadcast application. However, NH3 volatilization was 90% lower with injected manure, leading to greater N conservation. The third study (chapter 4) combined all of the data collected from the field lysimeters: gas emissions, overland flow and subsurface flow N loads, crop uptake, and soil storage into nitrogen budgets. To analyze the data, it was organized into two different manure budgets. The first budget covered January 2012 to September 2012, and the second budget spanned October 2012 to September 2013. Injection manure N balances were more difficult to close, and included a large proportion of ‘unaccounted’ N (50% and 68% of applied N for two accounting periods). Even so, results point to cumulative differences in nutrient use efficiencies that can be attributed to the greater conservation of ammonia-N with manure injection. There was an apparent build-up of soil N with manure injection that was not observed with broadcast application (in PSNT measurements). However, these trends were preliminary; over the two growing seasons covered by this study, these differences did not result in significant differences in corn yield or crop N removal. The final study (chapter 5) used the Integrated Farm System Model to simulate different manure management scenarios on a typical Pennsylvania dairy farm (100 milking cows, 80 ha). Data from field experiments measuring ammonia volatilization, crop uptake and nitrate leaching was used to verify the model. The model could then be used to evaluate different manure management strategies for crop production, environmental losses, and economics. Converting the operation from daily haul to 6 months of storage with broadcast application did not substantially change N losses to the environment. However, replacing broadcast manure application with shallow disk injection resulted in substantial conservation of ammonium-N in manure and greater manure N use efficiency by crops, but slightly exacerbated nitrate-N leaching losses. Increasing manure storage from 6 to 12 months and injecting manure reduced nitrate-N leaching reduced by 38% due to better timing of manure application to crop growth. However, when manure storage was expanded to 12 months, net returns were $422 less with subsurface injection compared to broadcast manure, whereas, with a 6-month storage, the difference in net return was $469 per year. The results of this research highlight the need for more long-term investigations of manure management at a field-scale. Long-term studies are important for establishing treatment differences. At field-scale some of these differences (ie. yield, crop uptake, runoff loads) might be more difficult to discern due to the highly variable nature of field research. Long-term study sites offer opportunities to further investigate BMPs like shallow disk injection. Overall, these studies find that shallow disk injection can be a positive alternative to broadcast applied manure, but that significant treatment differences are still hard to determine.