88523 Manual Chamber Sampling Strategies to Help Account for Temporal and Spatial Variability of N2O Emissions from Agricultural Cropping Systems.

See more from this Division: Workshops
See more from this Session: Measurement Issues for Nitrous Oxide Emissions from Soil
Thursday, November 6, 2014: 8:55 AM
Hyatt Regency Long Beach, Regency Ballroom EF
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Neville Millar, Michigan State University, Hickory Corners, MI and G. Philip Robertson, 3700 E Gull Lake Dr, Michigan State University, Hickory Corners, MI
Despite a strong mechanistic knowledge of the biotic and abiotic processes that generate nitrous oxide (N2O) in the soil, the inherent heterogeneity of agricultural landscapes, and the complex and interactive nature of the environmental and management factors that influence N2O emissions, make accurate quantification of N2O emissions challenging.

Due to multiplicative effects arising from the many interacting processes and factors that govern N2O in the soil, emissions of N2O are patchy; the spatial variability (CVs) at multiple scales frequently exceeds 100%. Elevated, short duration fluxes of N2O often rapidly follow management and environmental events such as nitrogen (N) fertilization, rainfall, tillage, and freeze-thaw cycles. A small number of these sporadic N2O peaks can contribute substantially to cumulative emissions over annual or longer time periods. Increasing the accuracy of N2O emissions measurements can help improve estimates of agricultural GHG inventories, better identify N2O mitigation opportunities, and advance modeling efforts for better prediction of future emissions.

Sampling regimes must therefore be designed to adequately capture the range of conditions conducive to N2O emissions in the area being investigated. At a field plot scale, typically, N, carbon (C), and oxygen availability (as controlled by water content of the soil) are the key soil attributes that control the pattern and magnitude of N2O producing processes.

Other than scientific rationale, resource trade-offs for measurement of N2O fluxes need careful consideration; the financial cost of measurement and analysis, the logistics associated with chamber or other sampling technologies, and the labor required for both. Where multiple treatment comparisons and /or smaller scale field experimentation are required, chamber technology with GC analysis is still the methodology of choice. Although automated systems are becoming more common, manual chamber operators in the field with sample transport to the laboratory for analysis still predominate.

Well-designed, manual chamber sampling strategies can address the temporal and spatial variability of N2O emissions from agro-ecosystems. In this presentation we will discuss some general scientific principles and logistical constraints that need to be considered before gas sampling begins. We highlight some of these issues, including chamber number and placement, and sampling timing and frequency, using case-studies in Michigan, Maryland, and Puerto Rico.

See more from this Division: Workshops
See more from this Session: Measurement Issues for Nitrous Oxide Emissions from Soil