[Strawbale] RV: [Paja] Datos sobre una bala de paja

[Robert Tom]

On Sat, 03 Nov 2007 05:50:38 -0400, Brian Waite <brian at brianwaite....uk>  
wrote:

>
> a strawbale building can have a zero or even negative carbon rating.

>    Another plus for SB: Research is now showing that because farmers are  
> not allowed to burn off straw, and have to plough it back into the soil,  
> this is creating a problem with soil fertility inasmuch as straw needs  
> fungal action for it to decompose and there is now an excess of fungi  
> building up in the soil, year by year, seriously depleting its'  
> fertility.

>>   2007/11/2, Rikki Nitzkin <rikkinitzkin at earthlink...>:
>>     I have gotten a request for exact figures on
>     -how much energy is spent in producing a bale
>     -how much CO2 is produced by it


I won't provide any figures for the embodied energy of straw bales simply  
because the variables are too wide-ranging to nail it down to any discrete  
amount.

For instance, in countries where straw is cut and baled by hand and then  
used in the immediate vicinity, the EE numbers will be substantially  
different than say, rice straw that is cut and baled in Texas or  
California where it is likely that huge tractors that are bigger than the  
homes of many people on this planet were used and then the straw might be  
trucked a hundred miles or more to the building site.

And it could easily be argued that since no one actually grows straw for  
the purposes of harvesting the straw, and since straw bales are a  
by-product of cereal grain production, the EE of strawbales could be  
considered to be negative. But I won't go into that.

The problem of soil fertility due to excess fungi (mentioned above) sounds  
spurious.

The initial stages of decomposition of straw and other carbon-rich  
materials like sawdust, wood chips requires nitrogen.

Nitrogen is a nutrient that is essential to plant growth and green leaves.

When straw is ploughed back into the soil, the initial stages of  
decomposition depletes nitrogen from the soil at the expense of any plants  
growing in it. Nitrogen-starved plants may be weak, growth-stunted and  
tinged with yellow, all of the signs of poor plant vigour.
Once the straw has decomposed, it is beneficial to soil health and  
structure and subsequently, to any crops growing in it. But that  
decomposition cycle usually takes longer than a single crop-growing season  
and land costs being so high, no farmers can really afford to let fields  
lay fallow so if nitrogen fertiliser is not added to the soil, crop health  
will suffer.

Traditionally, straw was taken off and used for animal bedding so that it  
would be mixed with  nitrogen-rich animal urine and manure before it was  
returned to the soil, hence no nitrogen depletion.


-- 
=== * ===
Rob Tom
Kanata, Ontario, Canada
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