Spatial variability of nitrous oxide emissions from an Australian irrigated dairy pasture

Abstract

Understanding spatial variability of emissions of nitrous oxide (N 2 O) is essential to understanding of N 2 O emissions from soils to the atmosphere and in the design of statistically valid measurement programs to determine plot, farm and regional emission rates. Two afternoon, 'snap-shot' experiments were conducted; one in the summer and one in the autumn of 2004, to examine the statistics and soil variables affecting the spatial variability of N 2 O emissions at paddock scale. Small, static chambers (mini-chambers) were placed at 100 locations over an 8,100 m 2 area of irrigated dairy pasture in northern Victoria, Australia. Chamber headspace was sampled for N 2 O and soil samples taken below each mini-chamber were analysed for soil nitrate (NO 3 -), ammonium (NH 4 + ) and other chemical and physical properties known to affect N 2 O emissions. The experiments took place immediately after the sequence of grazing, urea application and irrigation. Nitrous oxide emissions and soil variables were analysed using classical statistics to investigate the effect of soil variables on N 2 O emissions. Geostatistics were used to investigate spatial patterns of N 2 O emissions and soil variables over the measurement area. Nitrous oxide emissions were extremely variable; 45-765 ng N 2 O-N m −2 s −1 and 20-953 ng N 2 O-N m −2 s −1 for the two experiments with corresponding averages of 165 and 138 ng N 2 O-N m −2 s −1 . Nitrous oxide emissions showed spatial dependence up to 73 and 51 m for the two experiments. Nitrous oxide emissions showed significant correlation with soil nutrients in decreasing order of NO 3 -, NH 4 + and available-P concentrations. There was no significant correlation of N 2 O emissions with measured soil physical properties.

Spatial variability and hotspots of soil N<sub>2</sub>O fluxes from intensively grazed grassland

“…This relationship between soil NO − 3 and NH + 4 concentrations and N 2 O flux is also observed in similar studies (e.g. Turner et al, 2008). Our conclusion from the correlation analysis is that the high spatial variability of N 2 O flux across the grazed field is primarily due to the uneven distribution of nitrogen deposition in the form of animal waste.…”

The influence of tillage on N<sub>2</sub>O fluxes from an intensively managed grazed grassland in Scotland

“…N 2 O fluxes are believed to be driven primarily by the availability of nitrogen compounds in the soils (ammonium and nitrate) (Davidson et al, 2000) as well as physical properties of the soil such as WFPS, aerobic extent, soil type, temperature and compaction (Ball et al, 2008;ButterbachBahl et al, 2013;Choudhary et al, 2002;Davidson et al, 2000;Turner et al, 2008). The collection of these data on a temporal/spatial scale which would allow these models to be applied is not often logistically possible or affordable.…”

Spatio-temporal variability in N<sub>2</sub>O emissions from a tea-planted soil in subtropical central China

“…In this study, the median (13.6 mg N m −2 d −1 ) and CV (143 %) of N 2 O fluxes measured in the tea field were all found to be higher than those in other agricultural systems, such as grasslands (Ambus and Christensen, 1994;Turner et al, 2008),winter wheat (Ball et al, 1997;Clemens et al, 1999;Mathieu et al, 2006), and summer maize (Clemens et al, 1999); the findings were similar to the results for the wet season reported by Fu et al (2015), predominantly because of the optimal conditions for soil microbe activity…”

“…Accurate estimates of the amount and characteristics of N 2 O emissions are important prerequisites for reducing N 2 O emissions from agro-ecosystems (Akiyama et al, 15 2013;Ambuset al, 1994;Han et al, 2013;Kiese et al, 2003;Konda et al, 2008Konda et al, , 2010Lin and Han, 2009;Mosier et al, 1996Mosier et al, , 1998Turner et al, 2008). However, N 2 O is microbially mediated; it is produced via microbial processes of nitrification under aerobic conditions and denitrification under anaerobic conditions (Firestone and Davidson, 1989;Hayatsu, 1993;Mathieu et al, 2006;Venterea and Rolston, 2000; both the inherent complexities of N 2 O emissions and our own epistemic defects (Li et al, 2013).…”