Nitrous oxide emission from Australian agricultural lands and mitigation options: a review

Abstract

Increases in the concentrations of greenhouse gases, carbon dioxide (CO 2 ), methane (CH 4 ), nitrous oxide (N 2 O), and halocarbons in the atmosphere due to human activities are associated with global climate change. The concentration of N 2 O has increased by 16% since 1750. Although the atmospheric concentration of N 2 O is much smaller (314 ppb in 1998) than of CO 2 (365 ppm), its global warming potential (cumulative radiative forcing) is 296 times that of the latter in a 100-year time horizon. Currently, it contributes about 6% of the overall global warming effect but its contribution from the agricultural sector is about 16%. Of that, almost 80% of N 2 O is emitted from Australian agricultural lands, originating from N fertilisers (32%), soil disturbance (38%), and animal waste (30%).Nitrous oxide is primarily produced in soil by the activities of microorganisms during nitrification, and denitrification processes. The ratio of N 2 O to N 2 production depends on oxygen supply or water-filled pore space, decomposable organic carbon, N substrate supply, temperature, and pH and salinity. N 2 O production from soil is sporadic both in time and space, and therefore, it is a challenge to scale up the measurements of N 2 O emission from a given location and time to regional and national levels.Estimates of N 2 O emissions from various agricultural systems vary widely. For example, in flooded rice in the Riverina Plains, N 2 O emissions ranged from 0.02% to 1.4% of fertiliser N applied, whereas in irrigated sugarcane crops, 15.4% of fertiliser was lost over a 4-day period. Nitrous oxide emissions from fertilised dairy pasture soils in Victoria range from 6 to 11 kg N 2 O-N/ha, whereas in arable cereal cropping, N 2 O emissions range from <0.01% to 9.9% of N fertiliser applications. Nitrous oxide emissions from soil nitrite and nitrates resulting from residual fertiliser and legumes are rarely studied but probably exceed those from fertilisers, due to frequent wetting and drying cycles over a longer period and larger area. In ley cropping systems, significant N 2 O losses could occur, from the accumulation of mainly nitrate-N, following mineralisation of organic N from legume-based pastures. Extensive grazed pastures and rangelands contribute annually about 0.2 kg N/ha as N 2 O (93 kg/ha per year CO 2 -equivalent). Tropical savannas probably contribute an order of magnitude more, including that from frequent fires. Unfertilised forestry systems may emit less but the fertilised plantations emit more N 2 O than the extensive grazed pastures. However, currently there are limited data to quantify N 2 O losses in systems under ley cropping, tropical savannas, and forestry in Australia. Overall, there is a need to examine the emission factors used in estimating national N 2 O emissions; for example, 1.25% of fertiliser or animal-excreted N appearing as N 2 O (IPCC 1996).The primary consideration for mitigating N 2 O emissions from agricultural lands is to match the supply of mineral N (from fertiliser applications, legume-...

Mineralização e desnitrificação do nitrogênio no solo sob sistema plantio direto

“…Os resultados constantes deste estudo corroboram em parte com a literatura, mostrando que a aplicação do N-fertilizante no solo, além de promover reduções nas taxas de mineralização do N (carPenTerS-BoggS et al, 2000, marquez et al, 2000) aumentaram a emissão de N 2 O (Dalal et al, 2003;Sehy et al, 2003;WeiTz et al, 2001). …”

“…Em solos em condições favoráveis de umidade, a emissão do óxido nitroso pode chegar a 1,25 % do N-fertilizante aplicado (Dalal et al, 2003). Esta emissão pode parecer baixa comparada com a entrada de N no sistema, contudo para o ambiente essa quantidade pode ser elevada se considerar que o potencial de aquecimento global do N 2 O é de aproximadamente 300 vezes maior que o CO 2 (iPcc, 2001).…”

Seasonal dynamics in nitrous oxide emissions under different types of vegetation in saline-alkaline soils of the Yellow River Delta, China and implications for eco-restoring coastal wetland

“…For example, organic matter break-down and NO 3 − production could be stimulated in dry warm seasons, and the loss of N 2 O may be induced in the subsequent wet season when waterlogging occurs (Dalal et al, 2003;Liu et al, 2012).…”

Postharvest nitrous oxide emissions from a subtropical oxisol as influenced by summer crop residues and their management

“…Their activity is intensified in anaerobic environments or soil microsites with low O 2 availability (Moreira & Siqueira, 2006;Aita & Giacomini, 2007). In addition to these soil variables, temperature, water-filled pore space (WFPS), and pH have also been identified as N 2 O-production-controlling variables in agricultural soils, since they affect the activity of nitrifying and denitrifying bacteria as well (Maag & Vinther, 1996;Weitz et al, 2001;Dalal et al, 2003).…”

“…The inefficient use of N fertilizers and continuous legume cropping are mainly responsible for stimulating soil N 2 O emissions to the atmosphere since they increase the soil mineral N content and influence the soil labile C supply (Dalal et al, 2003;Gomes et al, 2009). In turn, soil tillage affects the majority of the N 2 Oemission-controlling soil variables and higher emissions of this GHG have usually been reported in soils under NT than under CT (Rice & Smith, 1982;Liu et al, 2007).…”