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By Richard Scharf

Over the last few years, the number of Agricultural Land Management (ALM) methodologies available to project developers has been increasing. The American Carbon Registry (ACR), Climate Action Reserve (CAR) and Verified Carbon Standard (VCS) have all added to agricultural project opportunities, including methodologies for reducing nitrous oxide emissions from nitrogen fertilizers, reducing methane emissions from rice cultivation, introduction of sustainable ag. land management, grassland management and a modular soil carbon quantification methodology.

N2O Emissions Reductions on Agricultural Crops

Perhaps the most notable recent additions to ALM methodologies include the streamlined N2O emission reduction methodologies approved by the American Carbon Registry, Climate Action Reserve and the Verified Carbon Standard, based on a recently published study (Hoben, et al., 2011). Since the methodology authors of the ACR and VCS methodologies are the same, and the same work influenced the CAR protocol, the three share these similarities:

  1. Simply reducing nitrogen fertilizer applications below business as usual rates for agricultural crops creates N2O emissions reductions without risk of reversibility.
  2. In the North Central Region (or NCR, which is essentially the corn belt) of the United States, where significant research on N2O emissions from agricultural soils used to grow corn has been published, a more precise emissions factor for corn crops is used than the IPCC default factor used for other areas. This means NCR projects are credited for greater emissions reductions than similar projects outside the region.

The main differences between the methodologies can best be summarized in a table.


The basic premise of these methodologies is that a percentage of the nitrogen fertilizer applied to crops is transformed to the GHG N2O. A simple mathematical model determines the amount of N2O emitted based on the application rate. The IPCC emissions factor of 1% is used in the ACR and VCS method on non-corn crops and corn crops grown outside the NCR, resulting in a conservative, linear model. Within the NCR on corn crops, all three methodologies use a peer-reviewed, non-linear model that results in greater emissions reductions over the IPCC default factor.

These N2O emissions reductions are irreversible, because the fertilizer applied for a harvested crop cannot be increased once the growing season is over. The reason leakage is either assumed to be zero or is likely going to be calculated at near zero is based on the value of the farmer’s crop relative to the value of any offset credits generated through emission reductions.

The potential for N2O emissions reduction projects is considerable. In the United States, farmers have traditionally over-applied nitrogen fertilizers to corn crops, due to yield goal methods for determining application rates and an aversion by farmers to change a tried and true method for achieving the crop yields they expect to produce. For most corn field in the US, more likely than not, the N fertilizer application rate can be reduced below current levels while maintaining crop yield.

Those who have developed other offset projects should find the relative simplicity of the new N2O emissions reductions methodologies refreshing. Farms with the most detailed fertilizer records will be easiest to document and verify.

The previously developed ACR methodology that is available for emissions reductions by reducing N fertilizer applications depends on the DNDC model. This obviously requires a project developer to have someone adept with this model on the team. However, since the DNDC model is now used by ACR’s new rice management methodology and CAR’s rice project protocol, more people are becoming familiar with the model.

VCS's Soil Carbon Quantification Methodology

In late 2012, VCS approved a multi-module methodology for the quantification of soil carbon and related carbon pools in ALM projects through direct measurement. With considerable experience in the direct measurement of soil carbon in AFOLU projects, ESI personnel recognize this methodology as an important source of guidance for projects and other methodologies where direct measurements of this carbon pool are necessary – whether for full quantification of baseline and project stocks, or to calibrate a model for the same purpose.

The methodology is applicable to ecosystem restoration projects, changes in agricultural practices, erosion reduction techniques and other project activities that are expected to affect the soil carbon pool, litter, plant biomass and other sources or sinks related to agricultural operations. The modular approach allows project developers to adapt the methodology for the type of land management being used. For example, litter and woody biomass pools may be important to projects involving grazing lands or agroforestry while inconsequential in row crop agriculture. Each is addressed in a separate module which can be used or ignored as deemed appropriate by the project developer.

Direct measurement of soil carbon stocks can be labor intensive and a number of informed decisions will have to be made by the project development team that will have a strong influence on the cost and accuracy of baseline and project monitoring measurements. It would be advisable to commence a project involving the direct measurement of soil carbon with input from a soil scientist skilled in soil mapping and the collection of soil samples, and who can properly train and supervise field crews.

Soil carbon is extremely variable across a landscape – especially landscapes where the soil is plowed or otherwise disturbed by earth moving equipment. A soil scientist who  understands  the  way  soil  carbon  content  varies  across  the landscape will  be  able to stratify the project area to reduce variation. Other important parameters, including the depth samples are taken and the methods for taking them should be determined with the input of a soil scientist.

The logistics of gathering the samples necessary will have a strong influence on the profitability of a project. Since the methodology recommends that samples should be  taken to the depth of 1 meter or more (unless professional opinion dictates a more appropriate depth) soils where hydraulic soil probes can easily be used will translate to lower cost sampling over soils where hydraulic probes are less successful. In the US, the Natural Resource Conservation Service or faculty at the  state’s  Land  Grant  University  will  be  able  to  tell  you  how  useful  such equipment will be. Generally speaking, rocky soils will present difficulties for taking samples compared to finer textured soils.

Rice Cultivation Methodologies

ACR approved its Voluntary Emission Reductions in Rice Management Systems methodology in May of 2013. CAR approved its first Rice Cultivation Project Protocol in December of 2011, with an update in June 2013.

The methodologies use similar project activities and both depend on the DNDC model to calculate CH4 emissions from soil in the baseline and project scenarios.  CH4 is the primary GHG considered in these methodologies, though the ACR methodology also credits increased energy and water use efficiency in the Mid- South growing region.

The methodologies are based on the fact that anaerobic soil organisms emit significant quantities of methane when soils are saturated with water, excluding oxygen from soil pores. Common rice cultivation techniques include the flooding of soils for long periods during the growing season to keep down competition from weed species. Reducing the amount of time during the growing season when the soils are saturated reduces the amount of CH4 emissions.

In addition to reducing the length of time the rice field soils are saturated, bailing and removing rice straw after harvest and removing rice straw after harvest removes the food for CH4 -emitting soil microorganisms, reducing emissions.

Currently, ACR’s methodology can be used in the California rice growing regions and  the   mid-south  region,  which  consists  of  the  Mississippi  Delta  region (including  Arkansas,  Mississippi  and  Missouri)  and  the  Louisiana  Gulf  Coast region. CAR’s protocol can only be used in the California rice growing region, at present.

For project developers and verifiers alike, a crop advisor familiar with regional rice cultivation practices is a vital part of the team. Much depends on proving when soils  were saturated and unsaturated, so devising strategies to do this effectively may depend on such expertise.

Avoided Conversion of Grasslands and Shrublands to Crop Production

ACR’s Methodology for Avoided Conversion of Grasslands and Shrublands to Crop Production was released in October of 2013, and is applicable to grassland and shrubland in the U.S. and Canada that are going to be converted to annual crop production.

Most of the carbon associated with grasslands and shrublands is in the soil, the primary carbon pool of concern for this methodology. Inclusion of above and below ground biomass is optional. The concept is that when soil is disturbed for annual crop use, SOC will oxidize and release CO2 until the soil reaches a new steady state with the new land management system.

Restrictions on land use are not as severe as in the USDA’s Conservation Reserve Program.  Land can still be used for grazing and hay productio  under the applicability conditions, though additional accounting for livestock emissions and equipment emissions from hay production activities would then be required.

Changes in carbon stocks that would have occurred in the baseline scenario are determined through the use of either process models (like DNDC, DAYCENT and APEX) or empirical models from peer reviewed literature, applicable to the project area. The initial carbon stocks are estimated through direct measurement or through regional soil carbon inventories.

For direct measurement of SOC, the methodology refers to ACR’s Tool for the Estimation of Carbon Stocks in Carbon Pools and Emissions from Emissions Sources. This measurement should be conducted or overseen by a soil scientist skilled in stratifying for SOC and in collecting bulk density samples in the field. Another important parameter that should be determined with the input of a soil scientist is the depth to which samples will be taken. This depends on the depths at which SOC concentrations are expected to change in the baseline scenario.

Keep in mind this methodology is for lands that would be converted in the absence of the project. Developers must show the land’s highest use is annual crop production and that the land is valued at least 40% greater when use as cropland over grassland/shrubland.

Sustainable Grasslands Management

The most recently released ALM methodology is Sustainable Grassland Management, which was approved by VCS and released in April of 2014. The methodology was developed based on degraded grazing land research in China, but may be applicable to degraded grasslands expected to remain the same or continue to degrade in the absence of the project. Evapotranspiration must be greater than precipitation. See the methodology (VM0026) for the full list of applicability conditions.

Project activities include sustainable practices, like improved rotation of grazers, limiting the number of grazing animals on degraded pastures, restoration of grasslands   by   replanting   with   perennial   grasses   and   instituting   proper management over the long term.

The two primary carbon pools likely affected by project activities are SOC, likely to   increase, and aboveground woody biomass, which may decrease.  Some management practices, if included, will also require monitoring of other emissions sources, including N2O emissions from fertilizers and emissions from biomass burning.

Increases in SOC are estimated either through the use of peer-reviewed models validated for the region where the project area is located. Another option is to use a  direct  measurement  approach,  which  must  be  an  established  method  or approved standard.

As with all projects where SOC is an important carbon pool, projects developed under this methodology would benefit with the guidance of an experienced soil scientist for stratification and soil sample collection and handling procedures.

The full methodologies are available for download from the carbon registries’ websites:

ACR:  Carbon Accounting — American Carbon Registry for the Methodology For Quantifying  N2O  Emission  Reductions  from  Reduced  Use  of  N  Fertilizer  on Agricultural Crops, Voluntary Emission Reductions in Rice Management Systems and the Methodology for Avoided Conversion of Grasslands and Shrublands to Crop Production.

CAR:  for the Nitrogen Management Project Protocol and the Rice Cultivation Project Protocol.

VCS:  for Quantifying N2O Emissions Reductions in Agricultural Crops through N Fertilizer Rate Reduction, Soil Carbon Quantification   Methodology   and   the   Sustainable   Grasslands   Management Methodology.

For additional information on Agricultural Land Management methodologies, please contact Environmental Services by subscribing to our sustainable website or emailing Richard Scharf at This email address is being protected from spambots. You need JavaScript enabled to view it..