CCRA-9: Soil Carbon and Soil Quality

Why are we interested in soil C, soil quality, grain yield, and ground cover?

There is intense interest in soil organic carbon (SOC) because of its potential for agronomic and environmental benefits. Namely, it is an indicator of soil quality and fertility, it can reduce erosion, reduce nutrient leaching and runoff, and improve infiltration and water holding capacity. Since SOC is the second largest C sink on the planet, it has the potential to offset anthropogenic C emissions, and it may be suitable for C sequestration payments.

Assessing SOC across our projects will involve baseline SOC measurement from which changes to SOC status will be compared for the various CAPS, soils, and climatic conditions being assessed during SANREM Phase IV. Implementation of CAPS is expected to alter SOC over time. Therefore, quantification of SOC at time zero and after CAPS implementation will serve as an indicator of soil quality improvement, the rate of change in SOC, and may serve as a basis for determining appropriate smallholder farmer credits for C sequestration due to CAPS implementation.

In addition, grain yield data is needed to assess the effects CAPS has on production capacity. Ground cover data should be collected to determine the extent to which the production systems meet the definition of CAPS and to enable estimates of the benefits of CAPS in reducing long-term erosion. It is expected that soil scientists will collect additional data needed to adequately describe their soils (pH, taxonomy, texture, slope, etc.) as part of their own research.

What will we do with the data?

We will obtain data on total organic carbon (TOC) and bulk density (ρb), as well as organic matter fractions at time zero and at the end of the experiment for both controls and CAPS to determine if our CAPS are increasing SOC. Time zero will begin with the implementation of a PI-recommended (aka “best bet”) CAPS trial. Sampling will be conducted on researcher managed plots and selected on-farm plots, and will include controls. Five hundred gram soil samples from researcher managed plots from depths 0-5 and 5-10 cm, along with ρb data, will be sent to Virginia Tech for organic matter fractionation of host-country soils. SOC fractions across sites will be compared and published under the proposed title “Comparison of smallholder SOC changes under CAPS in developing countries” with all contributing US and host country scientists as co-authors. If increases are found or projected through modeling studies, an analysis of the potential for smallholder payments under emissions trading will be published. Other papers are possible on cross-site findings.


  • Quantify total SOC stocks on a limited number of best-bet CAPS and control plots before and after CAPS implementation.
  • Quantify SOC fractions and grain yield with and without CAPS.


  • CAPS enhance soil quality and productive capacity

Data Collection

PI Parameter Depths (cm) Method Time
LTRA PIs Total organic C 0-30 or to limiting layer ≥2 cores from selected plots Time 0
LTRA PIs Bulk density 0-30 or to limiting layer As appropriate for your site Time 0
LTRA PIs Bulk density 0-5 & 5-10 cm Undisturbed soil cores, or as appropriate for your site Time 0 and end of expt.
LTRA PIs 500 g air-dry soil sent to Mulvaney for SOC fractionation 0-5 & 5-10 cm Composite ≥16 cores, pass field-moist samples thru 2 mm sieve, then air dry and send to ME Time 0 and end of expt.
LTRA PIs Grain yield N/A Weigh subsamples After harvest
LTRA PIs Percent ground cover N/A Line-transects After planting
LTRA PIs Above-ground biomass (biomass left on surface) N/A ≥2 quarter-meter quadrats, air dry After harvest
Mulvaney Total organic C 0-5 & 5-10 cm Dry combustion Time 0 and end of expt.
Mulvaney Particulate OM 0-5 & 5-10 cm Gregorich & Beare, 2008 Time 0 and end of expt.
Mulvaney Density fractions 0-5 & 5-10 cm Based on Gregorich & Beare, 2008 Time 0 and end of expt.