In his blog called Pannell Discussions, Professor Dave Pannell of the School of Agricultural and Resource Economics, at the University of Western Australia gave an old chestnut a run: "farmers are unlikely to benefit from... carbon sequestration in soils."
Prof. Pannell uses the following definition:
"Soil carbon sequestration is the process of transferring carbon dioxide from the atmosphere into the soil through crop residues and other organic solids, and in a form that is not immediately reemitted. This transfer or “sequestering” of carbon helps off-set emissions from fossil fuel combustion and other carbon-emitting activities while enhancing soil quality and long-term agronomic productivity. Soil carbon sequestration can be accomplished by management systems that add high amounts of biomass to the soil, cause minimal soil disturbance, conserve soil and water, improve soil structure, and enhance soil fauna activity. Continuous no-till crop production is a prime example." (Sundermeier et al., undated),
This definition of sequestration reflects the paradigm that held that organic matter input was the sole dynamic in the manufacture of soil carbon.But a definition should include reference to the activities of microbiological communities in response to rootmass activities.
He then tries to convince this farmer there won't be much in soil carbon for them:
1." It difficult to increase the amount of carbon stored in most cropped soils in Australia, even with zero till and when large amounts of stubble are retained (Chan et al., 2003)." My response to this is: Who can disagree with Dr Chan? He is a highly regarded soil scientist and one of the top 10 in the world for references to his work. He told us when we met at a farmers' meeting near Junee last year that we could put back the 30-40 tonnes of soil carbon lost from each hectare of cropping land, but it won't be easy. Who said no-till or zero-till was all that is needed to restore soil carbon? Do you have a reference? Have you seen CSIRO's ECOS magazine, March 08 edition? In it you will find the following: "One of the broadacre cropping properties north-east of Clermont in Queensland that is participating in the ASCAS (Australian Soil Carbon Accreditation Scheme) project has more than three times the amount of carbon in the farmed soil than there is under the surrounding native vegetation (149 tonnes of carbon/ha under native vegetation versus 516 tonnes of carbon/ha under the crop). As a result, the soil is far more productive. The wheat crop yielded 4 tonnes per hectare of grain with 13.5 per cent protein this year – well above the district average."
2." Soil sequestration is a once-off process," says Prof Pannell. "Once farmers change their management to increase soil carbon, it increases up to a new equilibrium level and then stops." Well we did some work on his in NZ. Not everyone agrees with the ‘steady state’ theory of soil development. “The steady-state has been defined as a temporary state of dynamic equilibrium in an open system. Any open system is continually directional in time,” said one contributor to the debate. (G. N. Park, Concepts in Vegetation/Soil System Dynamics — II. Post Steady-State, Tuatara: Volume 19, Issue 3, August 1972) Then there's Huggett's paper that rejects the notion of ‘steady state’ in favour of ‘evolution’, a process that never stops:
“Traditional soil formation theory sees a soil developing progressively under the influence of the environmental state factors until it is in equilibrium with prevailing environmental conditions,” says Huggett. But a new evolutionary view of soil growth makes the attempt to capture real conditions a soil would experience: random changes in systems, the notions of multidirectional changes and multiple steady states (as predicted by non-linear dynamics). It proposes that environmental inconstancy and non-linear behaviour in soil-landscapes lead to soil evolution, rather than to soil development. Soils ‘evolve' through continual creation and destruction at all scales, and may progress, stay the same, or retrogress, depending on the environmental circumstances.” (R. J. Huggett, “Soil chronosequences, soil development, and soil volution: a critical review”, School of Geography, University of Manchester, Oxford Road, Manchester M13 9PL, UK Question: If a dynamic disequilibrium is created by a change in management, and that disequilibrium runs its course, could it be possible that another change in management could create a further disequilibrium?
Professor Pannell makes the popular point ":3. It is difficult to measure the amount of carbon stored in soils. To do so in a convincing way would involve regular and ongoing costs, which would eat away at the modest once-off benefits."
But we say: " Why is soil carbon hard to measure? Soil carbon specialists measure it every day. And if "flux" is the problem, does it not have statistical properties, and as such, is it not manageable? As for the cost, in what context is it expensive to measure? In the scientific context or in the commercial world? On a one-off basis, or on negotiated price for thousands of tests? Do you know about the new measurement technology just now coming available? And how will cost affect demand when carbon dioxide is at $40/tonne?
The conversation was proceeding apace when the Professor brought out the big guns: His colleague John Passioura believes that increasing humus in the soil (e.g. from reduced tillage) ties up carbon, nitrogen, phosphorus and sulphur (Williams and Donald, 1957; Passioura, 2008) which would otherwise be available to increase crop yields. He estimates that in Australian cropping conditions, the cost of replacing these nutrients using additional fertilizer would be sufficient to wipe out any benefits from carbon sequestration even if the CO2 price was as high as $80 per tonne. He acknowledges that the error margin around this estimate is large, but even so there is clearly likely to be little or no net benefit at the sort of CO2 price currently being discussed: $20 to $40 per tonne.
Now there's a clue in there: the need to buy additional fertiliser. Part of the answer could be found in the following extract from Christine Jones's evidence before a Senate Select committee last month: "When we measured the nutrient levels in his paddock this year prior to him sowing his crop [again - Pasture Cropping], the phosphorous levels had gone up by a factor of five. The agronomist actually thought there was a laboratory error in the data. We relooked at that and at bare areas compared with areas under the grass, and it was correct that available phosphorous had gone up by a factor of five... Phosphorous fertilisers had been used over time, under 15 years of zero till in that area, and they just formed a phosphorous bank that had been inaccessible. A fortune has been spent on phosphorous fertilisers. That farmer will not need to apply phosphorous fertiliser, we do not know for how long but for several decades, because the microbes are releasing what has been built up. You mentioned before the issue with your conventional zero till and why it is that carbon does not work, nitrogen does not work and phosphorous does not work. Nothing works because you have to have a microbial bridge between plants and minerals in the soil. Plants cannot actually access those unless that is in place. Normally the carbon from plants feed the microbes that in turn bring nutrients back to the plants. We have destroyed all those associations in soil by loading it with toxic chemicals, basically. What has been in favour of its adoption is not only climate change but the rapidly increasing price of phosphorous, nitrogen and herbicides. That has encouraged farmers to look for alternatives to that system." MTC
Dave is a good bloke and has a great following on his blog. He'll see the light some day.
References:
Sundermeier, A., Reeder, R., Rattan Lal, R. (undated) Soil Carbon Sequestration—Fundamentals, http://ohioline.osu.edu/aex-fact/pdf/0510.pdf.
Williams, C.H. and Donald, C.M. (1957). Changes in organic matter and Ph in a podzolic soil as influenced by subterranean clover and superphosphate. Australian Journal of Agricultural Research 8(2): 179-189 .
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