Appendix 1 Limitations of NCAS data

Appendix 1 Limitations of NCAS data 1
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From “The Impact of Tillage On Changes in Soil carbon Density with Special Emphasis on Australian Conditions”, National Carbon Accounting System Technical Report No. 43, Australian Greenhouse Office, January 2005
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“In many instances the reviewed studies lacked important information necessary to evaluate changes in soil carbon... Specific information that was frequently missing and did not allow a full account of changes in soil carbon density from the examined trials.
a. Lack of information on plant biomasses in years preceding the cropping phase of a trial. Ideally years since clearing and the phase in the crop/pasture rotation should be identified. A legume phase in the crop may have better nutrient levels and so better biomass production.
b. The exact timing of burning of stubble is frequently not given. This is important as it determines how long the surface soil is protected by stubble cover and for how long the stubble is available for biological breakdown.
c. Information about the amount of stubble present in a cropping rotation was not presented in many studies. Stubble quantities will impact on soil carbon levels in the medium to longer terms, and therefore need to be considered when evaluating the effect particular management practices have on carbon stocks.
d. The grazing intensity and duration of stubble between crops. This can infl uence the amount of time that stubble will protect the soil surface and the amount of stubble available for biological breakdown.
e. Identification of the degree of soil disturbance before and during sowing.
f. Details of fertiliser application.
g. Frequently only minimal information is given on the grazing intensities and biomass levels in the pasture phases between cropping phases.
h. Soil conditions (physically and chemically) are often not stated at the commencement of the trial...



Appendix 1 Limitations of NCAS data 2

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From “Estimation of Changes in Soil Carbon due to Changed Land Use
National Carbon Accounting System - Technical Report No. 2 November 1999
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“There are a number of significant limitations in the paired site datasets. These include:
• Very few of the datasets have soil carbon data from below 20 cm depth in the soil profile.
• Only one dataset had information on soil carbon pools.
• Few of the reported data account for bulk density in calculations of C in the soil
profile. Without the bulk density profile, it is not possible to correctly calculate the soil C stock per unit land area.
• Criteria used for identifying paired sites or verifying that they may be paired sites are
usually not explicitly defined…
• Many of the datasets do not have accurate information on date and method of clearing
and development, land use history … land management practices and changes through time.
• Some datasets lack accurate site location data.
• Many of the datasets relate to sites that areno longer available or for which land use and land management details are not readily available..
• There are very few sites in the main areas of recent clearing…