[GSBN] Sharing thoughts on pros and cons of using straw as a building material.

Mon Jul 30 13:22:55 UTC 2018

I now see a typing error in my previous message, which I missed before.  I wrote:

NPK [nitrogen, phosphorous, phosphorous fertilizers]

I bet most of you figured out that the second, repeated 'phosphorous’ should have been ‘potassium’:

NPK [nitrogen, phosphorous, potassium fertilizers]

Sorry for my error.

Derek

Derek Roff
derek at unm.edu<mailto:derek at unm.edu>

On Jul 30, 2018, at 4:40 AM, Lars Keller <larskeller at gmail.com<mailto:larskeller at gmail.com>> wrote:

Thanks again Derek !

søn. 29. jul. 2018 kl. 20.19 skrev Derek Roff <derek at unm.edu<mailto:derek at unm.edu>>:
I love the things I learn from this group.  Stimulated by Carol’s comments and her article, I went looking for information on the relationship between the return/non-return of straw to the soil, and the effect on potassium and phosphorous levels in the soil.  This is obviously a complex question, and will vary with local conditions and farming techniques.  I found one significant surprise, in a research report about raising wheat in northern China.  The abstract says that adding "The NP [nitrogen and phosphorous fertilizers] and NPS [nitrogen and phosphorous fertilizers plus straw] treatments decreased [my emphasis] soil available K and slowly available K below the initial levels”.  Further, it says that "in the 0–10 cm soil layer, the NP, NPS, and NPK [nitrogen, phosphorous, phosphorous fertilizers] treatments decreased total K by 4.3%, 3.4%, and 0.4% than the initial concentration, respectively.”  This is a single study, which always added nitrogen and phosphorous fertilizers, and it found that returning straw to the soil reduced the loss of available potassium in the top layer of soil from 4.3% to 3.4% [per year].  In this situation, returning straw to the soil, by itself, didn’t come close to solving the potassium depletion problem.  However, the researchers report the best potassium levels were obtained by adding fertilizers with nitrogen, phosphorus, and potassium, plus returning straw to the soil.  https://www.sciencedirect.com/science/article/pii/S0378429014002767

I found another site, which estimated the amount of phosphate (P2O5), Potash (K2O) and Magnesium oxide (MgO) in a (metric) tonne of straw.  Winter wheat and barley were estimated to contain 1.2, 9.5, 1.3 kg per tonne for the three minerals.  Linseed straw was very close, at 1.6, 9.2, and no data.  The best figures were for Pea straw/haulm, at 3.9, 20.0, and 1.7 kg per tonne.  http://www.pda.org.uk/cereal-straw-nutrient-contents/

The next link estimates the financial market 2016 value of N, P, and K in a tonne of straw at $16.46 (US dollars) [my conversion from non-metric tons].  http://msue.anr.msu.edu/news/whats_the_nutrient_value_of_wheat_straw

For the farmer, there is obviously substantially more value in selling straw as building bales, or even bulk straw, than in the cost of the contained nutrients.

Derek

Derek Roff
derek at unm.edu<mailto:derek at unm.edu>

On Jul 29, 2018, at 10:09 AM, carolatkn at aol.com<mailto:carolatkn at aol.com> wrote:

Hello Lars and all

I agree that returning straw to farmland is very important - ideally after it has been used as feed or bedding for animals so that it has added nitrogen. The quality of agricultural soils has diminished at an alarming rate over the last 50 years. Very little organic matter left in a modern arable field. Yields are dwindling and the scientists use this as an excuse for GM but improving the soil would be a much better starting point.

A healthy soil is full of earthworms and these will take the straw based manure down without the need to plough.

In Europe burning straw in the field is banned. However, burning straw in an inefficient power station is supported in the UK with Government subsidy. Attached is an essay I wrote a few years back spurred on by this madness. I do argue that using straw for building one year in three would provide sufficient building material for all new houses to be super insulated, low energy demanding, carbon storing straw ones!

The climate/energy/soil health/food security/CO2 issues are all very closely intertwined. Some would argue that we shouldn't grow cereal crops at all. Locally grown vegetables or perennials and grass raised animals would use far less energy and be healthier for people and planet. Too much vested interest in agri-business for that to happen though.

all the best
Carol

-----Original Message-----
From: Lars Keller <larskeller at gmail.com<mailto:larskeller at gmail.com>>
To: Global Straw Building Network (private, with public archives) <GSBN at sustainablesources.com<mailto:GSBN at sustainablesources.com>>
Sent: Sat, 28 Jul 2018 15:19
Subject: [GSBN] Sharing thoughts on pros and cons of using straw as a building material.

Hi GSBNers
As I am soon expecting to be questioned about the reasoning behind using straw for buildings, I am eager to hear arguments pro and con.
Last year in Denmark we had an unusually low yield of straw due to rain.
This year in Denmark we are having an unusually low yield of straw due to drought. This is intensified by poor hay yields causing farmers to use straw also for fodder.

My thoughts:

First, ecologically speaking, after the cereal has been harvested, the straw belongs in the earth. If straw is not returned, nutrients such as Phosphorous and Potassium are removed, and the soil structure is negatively influenced due to the removal of Carbon.
In reality we are probably far from this situation being acted seriously upon almost anywhere. The main reason as always being money: the cost of replenishing the nutrients and the negative impacts of less carbon is estimated to be balanced out by the savings from not having to chop and plough in the chopped straw.

Second, you could argue that we are after all only delaying the return of the straw to the earth.

Third, you could argue that there are even bigger pressing problems at the moment for which straw is a very big step forward, such as substituting CO2 producing building materials with a CO2 sequestering material.

Fourth, straw is not a waste product from a commercial point of view. At least not in Denmark. It sells for app €90/ton straw ab farmer at 15% water content.

Best, Lars

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