“Recent research undertaken by Professor Mark Adams, Dean of the Faculty of Agriculture at
Sydney University, has found that biologically active soils can oxidise the methane emitted by
cattle carried at low stocking rates (Cawood 2010). The highest methane oxidation rate recorded in soil to date has been 13.7mg/m2/day (Dunfield 2007) which, over one hectare, equates to the
absorption of the methane produced by approximately 100 head of cattle.”

Prof Mark Adams had to radically reduce his claims because of a transcription error — it was 8.75kg of methane per ha per year, not 8750kg!

http://theland.farmonline.com.au/news/state/agribusiness-and-general/general/error-in-snowy-soils-carbon-report/1887462.aspx

“Prof. Adams affirmed that despite the significant rescaling of the figures, certain high country soils oxidised methane at sufficient rates to fully offset enteric methane production in low intensity grazing systems.”

ALSO I checked the source for Dunfield reference: “the record is 13.7mg/m2/day measured in tropical forests of India” — so not pasture and NOT 137mg/m2/day.

So that’s presumably the same as 100 cows per ha rather than 1000. Which is still very high relative to actual stocking rates.

“Cultivated soils support very low rates of methane oxidation compared to native ecosystems. ”

“In addition, soil compaction decreases methane oxidation”

So most standard overgrazed compacted pasture seem very likely be a net methane emitter. It’s still possible that holistic managed perhaps might perhaps be a sink, but it’s certainly not clear.

And in terms of a soil sink of CH4 by methanotrophic bacteria, I’ve had some recent contact with Prof Adams about his work on how healthy aerobic rangeland soils can actually absorb and convert (through oxidation) cow produced CH4 into CO2 and (more than) null the negative CH4 effects of the cow. These soils actually showed a net sink of CH4. But, Adams was studying rangelands that contained almost 50% forest woodlands. Adams’ (and Dunfield’s – Jones cite him above) research on CH4 sinking points to the microbiological succession pattern (from low-microbe-diversity, bacterial-dominated, compacted-slightly-anaerobic desert annual-plant soils to very high-microbe-diversity, fungal dominated, aerobic de-compacted forest perennial-plant soils) as key to estimating the soil’s capacity to absorb and convert CH4. Adams told me that the scale of the potential for CH4 soil sinks was incorrect in the article Jones quotes above and in a recent conf paper he shows that the rates of CH4 soil conversion to CO2 were exceptionally high in the soils he studied. So it may prove unusual that all soils will be able to absorb and convert ALL the cow produced CH4 above it. But the CH4 sinking by the aerobic methanotrophic bacteria is still very important and Adams says we should work to bump their numbers up. Adams’ and Dunfield’s work does provide a strong CH4 sink reason for having a lot of forest integrated into cattle ranching and making sure you have de-compacted AEROBIC grass soils. If you’re mob or high intensity grazing (Holistic Management) I can see a strong reason here for getting out immediately after you move the cattle to the next grazing cell and getting good aerobic innoculum microbiology extracts or teas onto the field right away.

Loved the info on organic matter content in early Australian soils. Because depletion takes decades, we don’t notice it until it’s ‘too late’. The good news is it’s not too late, if people start to take this stuff seriously – NOW!

http://www.ipcc.ch/graphics/syr/fig2-3.jpg

The middle figure is methane.

1. (A major issue) Diagram 3 is misleading – in particular the discussion of the graph, which claims that: “Measurements over the last 25 years show concentrations of atmospheric methane are merely exhibiting natural variation, with no significant trends in any direction (Fig.3)”. Note that the ordinate of figure 3 says: d(CH4)/dt – so this is the derivative of the methane concentration. This means that, if the graph is above the zero line, total atmospheric methane increases; if it is below the zero line, methane decreases. The graph certainly has ups and downs, but I’d estimate (I didn’t measure) that if we averaged it, we would get ~ +5, i.e. an annual atmospheric methane increase of about 5 ppbv/year. So, it is by no means correct to claim that the “concentrations of methane are exhibiting variation with no significant trends in any direction”.

2. (A very minor issue) Lightning is not the only inorganic source of Kjeldahl-Nitrogen. Some titanium minerals do photochemically fix a small amount of atmospheric nitrogen.