“For most of history, few things have mattered more to human communities than their relations with soil…For the past century or two, nothing has mattered more for soils than their relations with human communities, because human action inadvertently ratcheted up rates of soil erosion and, both intentionally and unintentionally, rerouted nutrient flows.” — Breaking the Sod: Humankind, History and Soil, J. R. McNeill and Verena Winiwarter
Importance of Carbon to Soil
The primary human activity impacting soils is agriculture, and the soil nutrient most severely depleted in quantity by agriculture has been carbon. Conversion from natural to agricultural ecosystems has depleted the soil organic carbon (SOC) pool by as much as 60% in temperate regions, and 75% or more in tropical ones. Such conversion has resulted in losses of 8 to 32 tons of carbon per acre from some soils, mostly oxidized and emitted into the atmosphere as carbon dioxide.
But depleting sinks of soil carbon is harmful in two ways.
Adding carbon dioxide — the primary greenhouse gas — to the atmosphere increases retained solar heat in the planetary system and results in disruptive weather extremes such as we have been experiencing. Since 1975 the global level of greenhouse gases has been rising and average temperature has been increasing at a rate of 0.3˚F to 0.4˚F per decade.