Thursday, January 08, 2009

STOP STOP PRESS!!!! 2% was wishful thinking

It is with apologies that we announce: WE THOUGHT IT WAS 0.2%/YR! but it appears we were wrong.
It appears that it was 0.2% over 10 years!

"This increase is greater than most carbon modelling suggests," said Dr Peter Fisher, head of the Victorian DPI's soil carbon unit, as he reported that a series of trials in VIC and NSW revealed that 0.2% increase in soil carbon in 10 years was possible.

The fact that the relationship between soil carbon and soil structure, porosity, water economy, and yield had to be established scientifically for Australian soils might surprise some, but it very timely.

We need to know a lot more about the study to understand the slight increase in soil C:

What were the land management techniques used to return the organic matter to the soil?Stubble? Stubble processed through animals? Stubble ploughed in? Compost? Each of these will have a different effect on carbon scores, depending on the availability of the organic matter to the microbes. And the state of health of the microbial community will affect the incorporation of the organic matter. Highly active soil will see stubble disappear in a few days. Inactive 'dead' soil will have stubble oxidise, with very little being incorporated. This would affect your carbon readings.
What other management techniques were in use on the paddocks? Cover crop? Fertiliser? Pesticides? Herbicides? Minimum Till? No Till?
What was the history of the paddocks? (Ie. a paddock which had been under perennial pasture until recently would be in the early stages of rapidly losing significant carbon while a long-cropped paddock would have plateaued at a low carbon point.
The models: how old is the data on which they were built?
Given what we know about microbial communities and their frontline role in manufacturing carbon, was there any analysis done of the paddocks to ascertain their background level of microbial activity before the trials commenced.

Dr Fisher thinks the 0.2% could stretch to 0.4% in 10 years. Even then, that could be worth $1000/ha.

1 comment:

Anonymous said...

I think 1% raise of humus in 10 years is doable!

With Ramial Chipped Wood (RCW) humus is built up 10 times faster than with crop residues or compost. This is because lignin in wood provides a basis for more stable humus than the carbon in crop material. 30% of RCW turns into stable humus, contrary to only 3-4% of compost.

A study in Belgium showed that with RCW you can build 4 tons of humus per year per hectare for the first 20 cm.

If your humus content was a typical 2%, and you want to bring it back to 3% how much humus carbon is added?

A first 20 cm of 1 hectare weights
2000 m3 x 1,34 = 2700 ton
2% = 54 ton humus
3% = 81 ton humus
Difference is 27 ton humus = 16 ton C

(carbon = 58 weight% of humus)

Growth of 4 tons dry weight humus = 2,3 ton C.

10 years x 2,3 ton C = 23 ton C.

So 4 tons of humus per hectare is more than sufficient for bringing the humus content from 2 to 3%!

1 ton C = sequestration of 3,65 CO2
23 ton C = sequestration of 85 ton CO2

For this you need to bring two times an amount of 300 m3 of RCW on a hectare of land (so 60m3 per year per hectare).

This is about the side production of 3 hectares of forestry (branches/pruning), normally considered as "waste" and very often burned.

Cities and village garden also produce enormous amounts of ramial wood "waste" that are currently flooding composting units.

I think it is more efficient to let the soil "compost" it directly.

For a real large application without forests or cities in the surroundings, you can think of a combined system of planting hedgerows or agroforestry. 50 trees planted on one hectare of agricultural land will reduce only the plantable surface with 10%, but in many cases the productivity stays the same, due to better and deeper good soil structure. 50 trees or 500 m of hedgerows of 2 meter width deliver 4-5m3 RCW per year per hectare. This quantity can be added to the crop residues, and in this way will still built up humus faster and more efficient (in terms of transport and handling) than adding this quantity of humus by means of compost.

Menno Houtstra