N2O emissions from managed organic soils

Summary

This methodology represents nitrous oxide (N₂O) emissions associated with organically managed soils. The data and calculation methodology is sourced from the IPCC, as published in Volume 4, Chapter 11 - N2O Emissions from Managed Soils, and CO2 Emissions from Lime and Urea Application of their 2006 IPCC Guidelines for National Greenhouse Gas Inventories.

The methodology

Emissions model

Nitrous oxide (N₂O) is produced naturally in soils through the processes of nitrification and denitrification. Nitrification is the aerobic (microbially-mediated) oxidation of ammonia to nitrate, and denitrification is the anaerobic microbial reduction of nitrate to nitrogen gas (N₂). N₂O is a gaseous intermediate in the reaction sequence of denitrification and a by-product of nitrification. Aside from the direct application of N to soils (which is otherwise a rate-limiting factor), human-attributable N₂O emissions arise from the mineralization of soil N following the drainage and management of organic soils. This methodology describes N₂O emissions associated with such organic soil management.

The methodology calculates N₂O emissions based on conversion factors which describe the rate at which quantities of soil-N (i.e. soil-assocaited nitrogen) are converted into quantities of N₂O-N (nitrous oxide-assocaited nitrogen) per unit of land area managed (i.e. kg / ha). Multiplying the area of land managed (e.g. ha) by this conversion factor, produces an estimate for the total production of N₂O-N attributable to that area of managed soil. This quantity is then converted to a quantity of N₂O emissions on the basis of the relative molecular masses of N₂O and N.

This methodology represents the IPCC Tier 1 approach.

Model data

Conversion factors for 9 organic soil management scenarios are provided within this methodology, differentiated by their climatic context (e.g., temperate, tropical, boreal) and land use (e.g. cropland, forest). Each scenario is represented by a direct N₂O-N conversion rate (kg / ha). In addition, this methodology uses two general constants for deriving emissions quantities from N₂O-N:

• molecular mass ratio of N₂O and N: the factor for converting a N₂O-N quantity into N₂O (44/28)

• global warming potential of N₂O: the factor for converting a N₂O emissions quantity into CO₂e - the quantity of CO₂ which would exert the same atmospheric warming effect.

Activity data required

N₂O emissions are directly proportionate to the area of land managed, which therefore needs to be specified in order to make an emissions calculation.

Calculation and results

This emissions calculated by this methodology represent those attributable to the specified area of land on which organic soils are managed.

The methodology calculates two emissions quantities: (1) the absolute quantity of N₂O; and (2) N₂O emissions expressed in terms of CO₂e.

Additional information

Nomenclature

IPCC advice states: Soils are organic if they satisfy the requirements 1 and 2, or 1 and 3 below (FAO, 1998) (World Reference Base for Soils, Food and Agriculture Organization of the United Nations, Rome, 1998): 1. Thickness of 10 cm or more. A horizon less than 20 cm thick must have 12 percent or more organic carbon when mixed to a depth of 20 cm; 2. If the soil is never saturated with water for more than a few days, and contains more than 20 percent (by weight) organic carbon (about 35 percent organic matter); 3. If the soil is subject to water saturation episodes and has either: (i) at least 12 percent (by weight) organic carbon (about 20 percent organic matter) if it has no clay; or (ii) at least 18 percent (by weight) organic carbon (about 30 percent organic matter) if it has 60 percent or more clay; or (iii) an intermediate, proportional amount of organic carbon for intermediate amounts of clay (FAO, 1998).

Climatic zones

The IPCC classification for global climatic zones can be seen using the gallery tab.

Related methodologies

A number of other methodologies focus on emissions from managed soils. These include those arising from the addition of urine and dung, urea, carbonates/lime and synthetic and organic fertilizers.