Soil N availability, rather than N deposition, controls indirect N2O emissions

Abstract

a b s t r a c tAmmonia volatilised and re-deposited to the landscape is an indirect N 2 O emission source. This study established a relationship between N 2 O emissions, low magnitude NH 4 deposition (0e30 kg N ha À1 ), and soil moisture content in two soils using in-vessel incubations. Emissions from the clay soil peaked ( < 0:002 g N ½g soil À1 min À1 ) from 85 to 93% WFPS (water filled pore space), increasing to a plateau as remaining mineral-N increased. Peak N 2 O emissions for the sandy soil were much lower ( < 5 Â 10 À5 mg N ½g soil À1 min À1 ) and occurred at about 60% WFPS, with an indistinct relationship with increasing resident mineral N due to the low rate of nitrification in that soil. Microbial community and respiration data indicated that the clay soil was dominated by denitrifiers and was more biologically active than the sandy soil. However, the clay soil also had substantial nitrifier communities even under peak emission conditions. A process-based mathematical denitrification model was well suited to the clay soil data where all mineral-N was assumed to be nitrified (R 2 ¼ 90%), providing a substrate for denitrification. This function was not well suited to the sandy soil where nitrification was much less complete. A prototype relationship representing mineral-N pool conversions (NO 3 À and NH 4 þ ) was proposed based on time, pool concentrations, moisture relationships, and soil rate constants (preliminary testing only). A threshold for mineral-N was observed: emission of N 2 O did not occur from the clay soil for mineral-N <70 mg ðkg of soilÞ À1 , suggesting that soil N availability controls indirect N 2 O emissions.This laboratory process investigation challenges the IPCC approach which predicts indirect emissions from atmospheric N deposition alone. Crown

A novel and effective technology for mitigating nitrous oxide emissions from land-applied manures

“…The gas analysis system used in our study was adapted from Redding et al (2016). It comprised an automated 32-channel gas manifold, with inlets connected to collapsible bags in which the pots were placed during gas analysis.…”

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“…This theory is consistent with Redding et al (2016) who studied N2O emissions from the same Vertosol used here under a range of N application rates soil and moisture conditions in a laboratory trial for 37 days and found that nitrification was almost complete at the end of the experiment. In the Sodosol, nitrification may have been inhibited without bentonite addition.…”

“…The results of this study match the results of Redding et al (2016) who investigated N2O fluxes from the same samples of Vertosol and Sodosol that were used in this study across a wide range of soil N concentrations and soil moistures. The authors showed that N2O fluxes from the Vertosol are minor up to 85% WFPS but increase strongly above this value and form a sharp peak between 85% and 93% WFPS.…”

“…It is also possible that the likely sealing effect caused by bentonite simulated the low soil O2 conditions at around 90% WFPS. Furthermore, Redding et al (2016) measured low nitrification rates in the Sodosol compared to the Vertosol and found N2O production in this soil to peak around 60% WFPS at low mineral N levels. As hypothesized in the present study, the authors discussed suppressed nitrification by NH3 accumulation as a possible reason for their finding.…”

“…However, this model has been challenged in recent years. It has been shown that peak N2O emissions occur at different %WFPS for different types of soil and for soils under different types of land-use (ButterbachBahl et al, 2013;Redding et al, 2016;Schaufler et al, 2010).…”