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Dynamic Controls on Field‐Scale Soil Nitrous Oxide Hot Spots and Hot Moments Across a Microtopographic Gradient
Author(s) -
Krichels Alexander H.,
Yang Wendy H.
Publication year - 2019
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1029/2019jg005224
Subject(s) - environmental science , nitrous oxide , atmospheric sciences , soil water , ponding , hydrology (agriculture) , growing season , spatial variability , soil horizon , denitrification , soil science , nitrogen , agronomy , ecology , chemistry , geology , drainage , organic chemistry , statistics , geotechnical engineering , mathematics , biology
Abstract Soil nitrous oxide (N 2 O) emissions are highly variable in space and time, making it difficult to estimate ecosystem level fluxes of this potent greenhouse gas. While topographic depressions are often evoked as permanent N 2 O hot spots and rain events are well‐known triggers of N 2 O hot moments, soil N 2 O emissions are still poorly predicted. Thus, the objective of this study was to determine how to best use topography and rain events as variables to predict soil N 2 O emissions at the field scale. We measured soil N 2 O emissions 11 times over the course of one growing season from 65 locations within an agricultural field exhibiting microtopography. We found that the topographic indices best predicting soil N 2 O emissions varied by date, with soil properties as consistently poor predictors. Large rain events (>30 mm) led to an N 2 O hot moment only in the early summer and not in the cool spring or later in the summer when crops were at peak growth and likely had high evapotranspiration rates. In a laboratory experiment, we demonstrated that low heterotrophic respiration rates at cold temperatures slowly depleted soil dissolved O 2 , thus suppressing denitrification over the 2–3 day timescale typical of field ponding. Our findings show that topographic depressions do not consistently act as N 2 O hot spots and that rainfall does not consistently trigger N 2 O hot moments. We assert that the spatiotemporal variation in soil N 2 O emissions is not always characterized by predictable hot spots or hot moments and that controls on this variation change depending on environmental conditions.