Higher N2O emission by intensified crop production in South Asia

Abstract

a b s t r a c tIntensification of food production in Nepal has been found to acidify the soils and hence increase their apparent propensity to emit N 2 O as measured by the N 2 O/(N 2 + N 2 O) product ratio of denitrification during standardized anoxic incubations (Raut et al., 2012). We hypothesized that this would lead to high N 2 O emission factors (EF), and tested this by measuring N 2 O emissions from fields on which intensified crop production (IC) had been practiced for the last 20 years, and adjacent fields having traditional crop production (TC) practices. The measurements were done every one to two weeks over a period of 12 months covering two to three cropping periods. On the sites with periodically flooded soils, the cumulated emissions for IC and TC were 15.41 and 7.23 kg N 2 O/ha, respectively. On the sites with permanently drained soils, the cumulated emissions were 5.43 and 1.46 kg N 2 O/ha (IC and TC). We used the available data on fertilizer levels to calculate an emission factor for the transition from TC to IC (EF I ); i.e. ∆N 2 O − N/∆N fertilizer , where ∆N 2 O-N is the cumulated emission in IC minus that in TC, ∆N fertilizer is the annual N input to IC minus that in TC.The EF values were 0.08 and 0.02 for the sites with permanently drained and periodically flooded soils, respectively. These factors are 2 to 8 times higher than the EF values used by IPCC to calculate emission as a function of fertilizer level. The high EF I appear to confirm our hypothesis that intensification will lead to higher emission of N 2 O than that predicted by the increase in nitrogen inputs, and that this is due to the soil acidification.

Summertime upper tropospheric nitrous oxide over the Mediterranean as a footprint of Asian emissions

“…Since intensified agriculture, characterized by high nitrogen fertilizer levels, are replacing traditional farming in many South Asian countries [ Rasul and Thapa , ], the denitrification process is enhanced by the use of nitrogen fertilizers leading to an increase of N 2 O emissions to the atmosphere [ Solomon et al , ]. N 2 O emissions are positively correlated with soil moisture [ Raut et al , ], and the relative soil nitrogen emissions (NO, HONO, and N 2 O) critically depend on the SWC [ Oswald et al , ] favoring NO and HONO when SWC ranges from 5 to 40% and favoring N 2 O when SWC ranges from 40 to 70%. Thus, the South Asian region is a hot spot of N 2 O emissions, especially during summertime when high precipitation events occur.…”

“…Since there is still a significant difference between the peak‐to‐peak amplitudes observed by GOSAT and calculated by LMDz‐OR‐INCA (1.8 ppbv and 1.5 ppbv, respectively), the N 2 O emission fluxes could be larger over Asia than the fluxes fixed in the emission inventory used by LMDz‐OR‐INCA. The inaccurate understanding of some processes such as soil acidification involved in soil N 2 O emission leads generally to an underestimation of the emission factor used to estimate soil emissions from agriculture [ Raut et al , ]. Consequently, this generates an underestimation of N 2 O emission fluxes, which are linearly affected by the emission factors [ Dobbie et al , ].…”

Atmospheric gas-phase composition over the Indian Ocean

“…Increasing N2O emissions (Fig. 7b) are believed to stem from intensified crop production and nitrogen fertilizer use as well as higher air temperatures (Raut et al, 2015). While not being the main emitter, East Africa is the region with the fastest increase of CH4 and N2O emissions among the regions discussed here (Fig.…”

“…Furthermore, the N2O emissions from managed soils are characterized by a pronounced seasonal cycle and interannual variability, primarily in response to meteorological conditions and nitrogen inputs. In particular, N2O emissions are correlated with soil moisture (Raut et al, 2015), leading to strongly enhanced emissions in South Asia during summertime when high precipitation events occur. Similar to the air pollutants discussed above, the overall CH4 and N2O emissions increased significantly over the period 2000-2015 from 135.7 Tg yr -1 to 182.4 Tg yr -1 and from 2.80 Tg yr -1 to 3.51 Tg yr -1 , respectively.…”

Emissão de óxido nitroso e matéria orgânica do solo em agroecossistemas de longa duração no cerrado

“…Entre as práticas agrícolas que interferem nas emissões de N 2 O, já são bem estabelecidas o preparo do solo, que altera a estrutura e aeração, bem como a concentração de oxigênio (Butterbach-Bahl et al, 2013), a deposição e a incorporação de resíduos orgânicos Schwenke et al, 2015;Zhang et al, 2015a), que aceleram o processo de decomposição e mineralização de N , dependendo da composição química dos resíduos vegetais . Além disso, características como o estádio fenológico das culturas (Hayashi et al, 2015), condições de acidez e fertilidade, temperatura do ar e do solo (Uchida et al, 2011;Butterbach-Bahl et al, 2013;Luo et al, 2013;Gelfand et al, 2015;Benoit et al, 2015), adição de fertilizantes nitrogenados minerais e a umidade do solo (Butterbach-Bahl et al, 2013;Deng et al, 2015;Harrison-Kirk et al, 2013;Pimentel et al, 2015;Raut et al, 2015;Soares et al, 2015) também interferem nas emissões de N 2 O.…”