Emissions of N2O and NO from fertilized fields: summary of available measurement data

The most important controls on NO emission include the N application rate per fertilizer type, soil organic-C content and soil drainage.Calculated global annual N₂O-N and NO-N emissions from fertilized agricultural fields amount to 2.8 and 1.6 Mtonne, respectively. The global mean fertilizer-induced emissions for N₂O and NO amount to 0.9% and 0.7%, respectively, of the N applied. These overall results account for the spatial variability of the main N₂O and NO emission controls on the landscape scale.

An extensive data set of measurements was used to develop models for calculating global N₂O and NO accounting for the main emission controls. This data set was recently summarized emphasizing the main regulating factors of N₂O and NO emissions (FAO/IFA, 2001; Bouwman et al., 2002). For both the data summary and the model development the Residual Maximum Likelihood (REML) technique was used rather than the commonly used multiple linear regression approach, as REML is considered more appropriate for handling problems of controlling factors in case of scant measurement and ancillary data or limited spatial and temporal coverage. By using more measurement data and models based on the main emission controls, the new inventories of NO and N₂O from agricultural fields amended with synthetic fertilizers and animal manure are hoped to be an improvement of previous inventories based on emission factors included in the EDGAR/GEIA inventory.

Influence factors on emissions

From the data set information from 846 N₂O emission measurements in agricultural fields and 99 measurements for NO emissions was used to describe the influence of the various factors considered in the data set. The N₂O and NO emissions were log-transformed to reduce the effect of extreme values. The residual distribution with log-transformed values is closer to a normal distribution than that for the untransformed values. Back-transformation yields values resembling a median value for the emission. Only those factors having a significant influence (Wald statistic, P<0.005) on N₂O and NO emissions were included in the models.

For N₂O these were:

• Environmental factors (climate, soil organic C content, soil texture, drainage and soil pH);
• Management-related factors (N application rate per fertilizer type, type of crop, with major differences between grass, legumes and other annual crops);
• Factors related to the measurements (length of measurement period and frequency of measurements).

The most important controls on NO emission include:

• N application rate per fertilizer type
• Soil organic-C content
• Soil drainage.

Models

All the factors with significant effects on emissions were used to develop models for N₂O and NO. The emission of N₂O-N or NO-N in kg ha-1 is calculated as follows. The models for N₂O and NO developed with the REML procedure summarize measurement data from the literature and account for the heterogeneity of environmental and management factors determining N₂O and NO emissions from agricultural fields. The REML-based models were used to calculate global emissions and FIE from fertilized crops and grasslands in a geographical information system with 0.5 by 0.5 degree resolution data on soil properties (Batjes, 1997), climate types (FAO, 1996a), rice-growing areas, leguminous crops, other (upland) crops and grasslands (Zuidema et al., 1994). These were updated with statistical data for 1995 on land use (FAO, 2000), combined with country data on mineral N-fertilizer use (FAO, 2000; FAO/IFA/IFDC, 1999; IFA, 1999), animal populations for dairy and non-dairy cattle, pigs, poultry, sheep and goats (FAO, 2000), and animal N excretion and animal-waste management systems (FAO, 1996b; Mosier et al., 1998).

In the absence of information on application rates for each grid cell, we used country data for each crop type on N application rates and areas actually fertilized for estimating global emissions. We estimate that about 69% of the world?s arable land and 8% of grasslands are fertilized with N fertilizers and manure.

Emissions

Calculated global annual N₂O-N and NO-N emissions from fertilized agricultural fields amount to 2.9 and 1.6 Mtonne, respectively. The global mean fertilizer-induced emissions for N₂O and NO amount to 0.9% and 0.7%, respectively, of the N applied. These overall results account for the spatial variability of the main N₂O and NO emission controls on the landscape scale. The 95% confidence interval for N₂O-N emissions, computed with multi-linear regression, is –40% to + 70%. The uncertainty of the REML model is probably smaller than that for the regression model as it is based on a larger data set. The number of complete records in the data set for NO is too small to estimate the uncertainty.

Our global aggregated estimates for FIE for N₂O for different fertilizer types are considerably lower than the default global FIE proposed by IPCC/OECD/IEA (1997), while our estimate for the FIE for NO exceeds the one proposed by Veldkamp and Keller (1997). The uncertainty in our estimates is much smaller than that of IPCC/OECD/IEA (1997). In addition, the global extrapolation using the REML models indicates a high spatial variability of mean annual N₂O and NO emissions, with important differences in both total emissions and the FIE between regions resulting from heterogeneity of management and environmental conditions. The data set of measurements and the approach followed in this study could therefore form a basis for an update of the IPCC methodology (IPCC/OECD/IEA, 1997).

Download figures

These figures contain worldmaps with emission data.

Figure 1: Estimated annual N2O emission for 1995 from synthetic fertilizers and animal manure used in wetland rice fields (a) , leguminous crops (b), other upland crops (c) and grasslands (d). Note that the emission is an annual estimate. High values may be caused by high cropping intensities, such as in China. Low values may be the result of low cropping intensities. The emission rates per hectare of harvested land may thus differ from those presented here.

• download figure 1 (JPG, 267 KB)

Figure 2: Estimated annual NO emission for 1995 from synthetic fertilizers and animal manure used in wetland rice fields (a) ,upland crops (b) and grasslands (c). Note that the emission is an annual estimate. High values may be caused by high cropping intensities, such as in China. Low values may be the result of low cropping intensities. The emission rates per hectare of harvested land may thus differ from those presented here. The NO model has no class value for leguminous crops. Therefore leguminous crops are included in upland crops for NO.

• Download figure 2 (JPG, 141 KB)

Download data

• n2o-no-data.zip (150KB): The data set of measurement data, including the references used
• ASCII files containing global N2O and NO emissions as a 360 (rows) by 720 (columns) matrix. The first cell is -179.5N + 89.5 N. Coordinates represent the bottom-left corner of each grid cell. The following files can be downloaded: n2o_no-emission_files.zip (114KB).

This zipfile contains the following ASCII files:

More information

• See also Modeling global annual N2O and NO emissions from fertilized fields

References

• Batjes, N.H. (1997) A world dataset of derived soil properties by FAO-UNESCO soil unit for global modelling. Soil Use and Management 13: 9-16.
• Bouwman, A.F., L.J.M. Boumans, and N.H. Batjes (2002) N2O and NO emissions from fertilized fields. Summary of available measurement data. Global Biogeochemical Cycles (in press).
• Bouwman, A.F., L.J.M. Boumans, and N.H. Batjes (2002) Modeling global annual N2O and NO emissions from fertilized fields. Global Biogeochemical Cycles (in press).
• FAO (1996a) Food production and environmental impact, World Food Summit, Tech. Background Doc. 11., Food and Agriculture Organization of the United Nations (FAO), Rome, 27 pp.
• FAO (1996b) World livestock production systems. Current status, issues and trends, FAO Animal Production and Health Paper 127, Food and Agriculture Organization of the United Nations (FAO), Rome, 83 pp.
• FAO FAOSTAT database collections (2000) Food and Agriculture Organization of the United Nations (FAO), Rome.
• FAO/IFA (2001) Global Estimates of Gaseous Emissions of NH3, NO and N2O from agricultural land. Food and Agriciculture Organization of the United Nations (FAO) / International Fertilizer Industry Association (IFA), Rome, 106 pp.
• FAO/IFA/IFDC (1999) Fertilizer use by crop, Fourth Edition, Food and Agriculture. Organization of the United Nations (FAO), International Fertilizer Industry Association (IFA) and International Fertilizer Development Center (IFDC), Rome, 52 pp.
• IFA (1999) Nitrogen - Phosphate - Potash, IFADATA statistics from 1973/74-1973 to 1997/98-1997, including separately world fertilizer consumption statistics, ), International Fertilizer Industry Association (IFA), Paris.
• IPCC/OECD/IEA (1997) Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories. Organization for Economic Cooperation and Development (OECD), Paris.
• Mosier, A.R., C. Kroeze, C. Nevison, O. Oenema, S. Seitzinger, and O.V. Cleemput (1998) Closing the global atmospheric N2O budget: nitrous oxide emissions through the agricultural nitrogen cycle. Nutrient Cycling in Agroecosystems 52:225-248.
• Veldkamp, E., and M. Keller (1997) Fertilizer-induced nitric oxide emissions from agricultural soils. Nutrient Cycling in Agroecosystems 48: 69-77.
• Zuidema, G., G.J.v.d. Born, J. Alcamo, and G.J.J. Kreileman (1994) Simulating changes in global land cover as affected by economic and climatic factors. Water Air and Soil Pollution 76: 163-198.