Tuesday, November 27, 2012

Soil C sequestration causes emissions and degrades soil - Scientific Report

Believe it or not! Sequestering soil carbon is environmentally hazardous, and causes CO2 emissions, according to a report released this month in Soil Research. Working over the chemistry of discontinued 25 year trials of cropping practices, the conclusion was reached that 'there is an environmental and C cost associated with C sequestration'. It works like this: to increase C you must use N. When you add N  you reduce pH and make the soil acidic. To counter this degradation of the soil you have to add lime. Adding lime costs money, releases CO2, and causes emissions during mining, processing and transport. The paper runs the numbers on the additional costs for N and Ca vs the tiny amounts of C anticipated to be sequestered and it's just not worth it. Theoretically.

What does the CSIRO think? In addition to drawing down CO2 from the atmosphere, the CSIRO* lists these essential soil health benefits of increased soil carbon:

Consequences of depletion of soil organic matter:

·      Depletion of plant nutrients including N, P and S.
·      Increased soil bulk density (compaction).
·      Loss of aggregate structure.
·      Decreased water-holding capacity and hydraulic conductivity.
·      Decreased cation-exchange capacity.
·      Increased surface erosion.
·      Increased leaching of pesticides and heavy metals.
·      A decline in soil biological activity and diversity.
·      Declines in crop yields and quality.
Improving SOM levels will help reverse deleterious consequences (above). Improvements to:
·      soil structure,
·      soil fertility,
·      nutrient retention,
·      water holding capacity, and
·      reduced soil erosion.
·      soil physical properties such as aggregation, water infiltration, hydraulic conductivity and compaction
·      greater productivity and crop yields
·      reduced inputs of fertilizers, pesticides and water.

Mitigation options have numerous co-benefits:
·      food security,
·      environmental sustainability and
·      farm profitability

*Jonathan Sanderman, Ryan Farquharson and Jeffrey Baldock, Soil Carbon Sequestration Potential: A review for Australian agriculture, CSIRO Land and Water, 2010

No comments: