Sunday, March 9, 2008

Are you aware?

Are you aware of the report published in dec 07 by Khan et al of the U. of Illinois which confirms that the long term use of chemical fertilizer releases carbon from soil and reduces soil organic matter? This was also confirmed by studies released by rodale and Iowa State in the first quarter. I think people are generally aware of the destruction of water quality in the gulf and chesapeake Bay caused by row cropping but are they aware of the tie to CO2 emission?

Message from Donald Kerstetter

3 comments:

Dewayne Johnson said...

"The Myth of Nitrogen Fertilization for Soil Carbon Sequestration" was published in the November/December 2007 issue of the Journal of Environmental Quality. The research was conducted by U of I soil scientists Saeed Khan, Richard Mulvaney, Tim Ellsworth, and Charlie Boast. Abstract: http://jeq.scijournals.org/cgi/content/abstract/36/6/1821

Mark Anderson-Wilk said...

A study on carbon sequestration and rangelands (Derner and Schuman, Journal of Soil and Water Conservation 62(2):77-85) found that "The benefits of increased SOC sequestration with N-fertilization are offset, however, by emissions of CO2 and N20 in the fertilizer process, as well as the enhancement of NOx emissions and reduction of CH4 uptake in soils."

Jon said...

If extensive tillage was part of the crop production system on the Morrow plots (and I have to assume it was)then the soil biology was most likely dominated by bacteria. The bacteria, in the presence of excessive oxygen from aeration during tillage and the physical demolition of soil aggregates would have fed on the SOC. Bacteria are notoriously wasteful feeders, respiring the majority of carbon they ingest. Excessive use of nitrogen fertilizer would have lowered the C:N ratio of the system, further facilitating the breakdown of SOC and crop residues that should have been contributing to SOC. Tillage "stirs the fire" and results in the biologic burning of SOC. Nitrogen, in this case, is merely an accelerant that enables the fire to burn more fiercely. Use of nitrogen fertilizer in combination with no tillage and a diverse crop rotation would most certainly increase SOC, not cause its' decline. I agree that we should look at ways to judiciously use nitrogen fertilizer because it is expensive, unsustainable and disrupts the optimal function of the soil food web but it should not be blamed for the decline in SOC. We need to look at our crop production systems as a whole and understand how they impact soil aggregates (habitat for most soil life) and the soil food web to understand how to manage SOC.