The New South Wales Department of Primary Industries has an interesting 60-page guide to growing soil organic matter in pastures.

"This book is based on findings from a three year project investigating soil carbon levels in pastures under different management practices in south east NSW. It is designed to be of practical use to farmers who want to increase their soil carbon levels. It includes basic information on soil carbon and reports the project's findings regarding the impact of pasture management on soil carbon."

It can be downloaded from here:

http://www.dpi.nsw.gov.au/agriculture/resources/soils/soil-carbon/increa...

This is a mapping project for measured changes in soil carbon content over time (as well as Soil Carbon Challenge entries, in yellow). The purpose is not to aggregate "offsets" or to make broad predictions, but to show what's possible as verified by actual measurements. When the purpose is to show what is possible, rather than to generate a broad-scale prediction or quantify carbon offsets, questions of statistical reliability are less troubling.

There are many stories that are told about soil carbon, and what its possibilities are. Much conversation on this topic has substituted assumptions for observations. Repeated measurements at the same location appear to be rare.

If you have data you would like to include, or can suggest good data, please contact us, info at soilcarboncoalition dot org, or you may start with a data form attached below.

Carbon gains and losses are expressed in metric tons of carbon (not carbon dioxide) per hectare per year, or as annual percentage increase where bulk density measurements have not been taken.

Go to the map

Conversions

To convert carbon to CO₂, multiply by 3.67. For CO₂ to C, multiply by .273. (The molecular weight of CO₂ is 16 for each oxygen atom, and 12 for the carbon atom, so the ratio of CO₂ to C is 44:12.)

To convert hectares to acres, multiply by 2.47. To convert acres to hectares, multiply by .404.

To convert metric tons C per hectare to metric tons CO₂ per acre, multiply by 1.52. To convert tons CO₂ per acre to tons C per hectare, multiply by .658.

In the Sacramento Delta of California, a freshwater tidal marsh thick with tules and other marsh vegetation formed carbon-rich peat soils 60 feet deep in places. In the 1870s, farmers began to build dikes, drain the marshes, burn the tules, and farm the peat soils.

With the peat exposed to air, it oxidized rapidly. The soil surface descended below sea level, sometimes by inches per year. The levees were reinforced, and the water table lowered some more by pumping, so that farming could continue. By the 1990s the soil surface on some of these peat lands was down to 15, 20, and even 25 feet below sea level. The biological crater left by the oxidation of peat soils in the Delta had grown huge, about the size of the debris flow from the eruption of Mount St. Helens in 1980.

If you double the height of a levee or dike, you quadruple the water pressure on it. If or when these levees fail, salt water from San Francisco Bay will fill the crater, compromising the water supplies for about two-thirds of California, including much of the irrigated agriculture of the central valley.

About ten years ago the US Geological Survey began a small experiment to see if this loss due to oxidation could be reversed. On Twitchell Island, about 15 feet below sea level, they flooded the land shallowly, and put in some clumps of tules and cattails. As the plants grew, they raised the water level. After ten years, this experiment has built two feet of peat soils that you can stand on, and recording a carbon accrual of 10 metric tons C per ha per year.