Effects of Management on Selected Soil Properties and Nitrous Oxide Fluxes in Dairy Cropping Systems
Open Access
- Author:
- Ball, Emily Paige
- Graduate Program:
- Soil Science
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 13, 2019
- Committee Members:
- Mary Ann Bruns, Thesis Advisor/Co-Advisor
Heather D Karsten, Committee Member
Curtis Dell, Committee Member - Keywords:
- Nitrous Oxide
N2O
Redox Potential
Redox
Eh
Agricultural Management
Soil Properties
No-Till
Manure
Cover Crops - Abstract:
- This thesis investigates selected soil properties and management decisions and their effect on nitrous oxide (N2O) emissions from agricultural soils. Nitrate, an inorganic form of N, is extremely mobile in soils, making it susceptible to loss through processes like denitrification. Denitrification is an anaerobic microbial process that reduces nitrate to N2 or incompletely to N2O, a potent greenhouse gas. The experimental site for this research was the Sustainable Dairy Cropping System (SDCS) located at Penn State’s Agronomy Farm. Chapter one is a review of the literature on nitrogen (N) cycling in agriculture, N loss pathways and the management and environmental factors affecting denitrification. This process is driven by soil properties, nitrate availability, and other factors. A prior study in this experiment in 2015 and 2016 found that the driving factors for N2O emissions in some of the same treatments were explained by days after manure application, growing degree days (GDD), and manure rate. Research on the effects of prior crop and management on N2O emissions in a typical PA dairy cropping system is described in chapter two. Labile carbon, total carbon, inorganic N species, and other environmental data were measured to determine their impact on measured N2O fluxes in 2017 and 2018. However, the measured soil and environmental properties in this experiment were not able to explain the observed patterns in N2O emissions through a regression analysis. The highest N2O fluxes were measured in 2018 in Corn after two years of Alfalfa (Medicago sativa) + Orchardgrass (Dactylis glomerata). Cumulative emissions were more than six times higher than those measured in treatments without a winter cover in the same year. Based on findings in 2017, chapter three investigates the impact of termination timing of Alfalfa+Orchardgrass on spring N2O fluxes and soil properties in 2018. This management decision is becoming more popular in the Northeast as spring conditions become wetter, making the proper timing of spring management events difficult. The findings from this experiment are promising for farmers interested in adopting this management practice as yields did not significantly differ from the subsequent corn crop and although they did not significantly differ, spring cumulative emissions from the spring terminated treatment were more than three times those from the fall terminated treatment. Because N2O emissions were not measured in the fall, however, the comparison of the two treatments in this study was not comprehensive. Chapter four described an investigative study on redox potentials in unsaturated agricultural soils. Equipment constraints and spatial variability made understanding and interpreting these results difficult. There were diurnal trends exhibited in some treatments, reflecting diurnal changes in soil moisture but not others. There also seemed to be stratification in depth, although this trend also differed across treatments. Overall, there is evidence that different crops can facilitate different redox environments and in turn, different microbial processes. However, more research and equipment advances need to take place before redox potential could be considered a useful indicator of microbial processes in unsaturated soils. Finally, the conclusions summarized the major findings of each of these experiments and discussed the impact of sustainable management practices on improving soil resiliency. Implementing sustainable practices like cover cropping and no-till can improve soil, although trade-offs of higher N2O emissions may result. Further research on these practices and their impact on soil properties is necessary as the effects of climate change are becoming more apparent.