Mitigation of postharvest nitrous oxide emissions from soybean ecosystems: a review

Abstract

In this review, the current knowledge of nitrous oxide (N 2 O) emissions from soybean (Glycine max (L.) Merr.) ecosystems, particularly on postharvest N 2 O emissions, is summarized and controlling factors of postharvest N 2 O emissions from soybean ecosystems are discussed. A new biological method to mitigate N 2 O emission is also presented. The latest (2006) guidelines of the Intergovernmental Panel on Climate Change (IPCC) concluded that N 2 O emissions derived directly from biological nitrogen (N) fixation were not significant in legume crop ecosystems. The default N 2 O emission factor from biological N fixation was revised to zero, whereas the default N 2 O emission factor for the decomposition of legume crop residues (postharvest N 2 O emissions) was the same as that for nonlegume crop residues (1%). From previously measured field data, the percentage of N in soybean residue emitted as N 2 O after harvest was calculated to determine emission factors. Values ranged from 0.0-10.0% (average 1.3% ± 2.7%, median: 0.2%), indicating relatively low emission factors. The average emission factor calculated for N 2 O emissions from N in soybean residues was slightly higher than the default emission factor for N in crop residue specified in the guidelines. However, the volume of field-measured postharvest N 2 O emissions in soybean ecosystems is low compared with data for N 2 O emissions during the crop growing season. Previous field-measured data demonstrated that N 2 O emissions often peaked sharply immediately after the harvest. However, values for N 2 O fluxes in the currently available field data were determined on a weekly or monthly basis. This large time gap between samplings may have resulted in underestimation of postharvest N 2 O emissions in soybean ecosystems. More detailed field studies on postharvest N 2 O emissions from soybean ecosystems are needed. Nodule decomposition is the major source of postharvest N 2 O emissions in soybean ecosystems. A new microbiological method was recently developed to mitigate postharvest N 2 O emissions from soybean ecosystems utilizing N-fixing bacteria with increased N 2 O-reducing activity (increased expression of nosZ). This approach may potentially be applied to other leguminous crops and non-legume ecosystems. Ongoing research on the relationships between soil N 2 O emissions and nosZ may reveal a new method for N 2 O mitigation in the future.

Nitrous oxide emissions from clover in the Mediterranean environment

“…This can be explained by the significant multiple linear regression found for Phase 1 between N2O, N-NO3, N-NH4 and soil temperature, where the N-NO3 is the variable with the highest predictive capability (P<0.001). During Phase 2 the N2O flux magnitude was stable, likely due to the constant degradation rate of the roots nodules (Uchida and Akiyama, 2013). Cumulative N-N2O emissions reported by Barton et al (2011) from a semiarid climate were more than three times lower that our value (127 g N-N2O ha -1 for 350 days).…”

“…Legume residues decomposition is often fast as the carbon/nitrogen (C/N) ratio is low and the main sources of N2O from N2-fixing crops is the decomposition of the residues (Van Der Weerden et al, 1999;Baggs et al, 2000). Root nodules C/N ratio is lower than the ratio of the other type of plants residues, thus in the soil decomposition of nodules is very fast and can be the major source of N2O during the postharvest period (Uchida and Akiyama, 2013). An experimental field was cultivated with clover (Trifolium squarrosum L.) with the aim to assess the magnitude of N2O daily flux and cumulative emissions in the Mediterranean environment.…”

Azolla cover significantly decreased CH4but not N2O emissions from flooding rice paddy to atmosphere

“…N 2 O is a byproduct or an intermediate product of microbial nitrification and denitrification on the N cycling in soil-plant ecosystems (Cheng et al 2004a, b). There are many studies showing N 2 O emissions from symbiotic N 2 fixation plants, such as leguminous crops and acacia trees as being larger than nonsymbiotic N 2 fixation plants (Arai et al 2008;Mori et al 2010;Uchida and Akiyama 2013;Zhang et al 2014). The N 2 O emission from soybean ecosystems could be mitigated by inoculation of high N 2 O reductase N-fixing rhizobium (Akiyama et al 2016).…”

Net Greenhouse Gas Budget and Soil Carbon Storage in a Field with Paddy–Upland Rotation with Different History of Manure Application

“…It could be caused by increases in soil temperature and moisture for the period. The increase in N 2 O flux after harvesting (October) could be derived from decomposition of plant residue and nodule [23]. There was no clear tendency between the N 2 O fluxes from inter-row and from those on the rows with different conditions of the surface soil such as soil moisture across the plots (Figure 2).…”