An update on the #transitiontoAction (T2A) project
So just over a month ago I did my first unboxing video and revealed that I had received a carton of cut up cotton. The fate of this cotton was to be buried in the accompanying soil from a Goondiwindi cotton farm and look at how it degrades and if there is any impact on some soil properties that are important to crop production. The purpose of the #transitiontoaction (T2A) project is to try and divert cotton end of life material and, rather than bury it in landfill, apply it back to the soils where cotton is being grown.
In practice this might sound easy, but there are risks with returning fabric to soils. Some of these are easy to recognise, such as, if the material is too big or does not break down it could cause issues for farm machinery. Some issues are less well understood, such as what effect, if any, will the dyes in the material have? Will the weave of the cotton matter or what happens if the fabric is a poly cotton? The purpose of the experiments we are conducting at UNE is to try and answer some of these.
Breathing soils
The first experiment we are doing measures the breakdown of the cotton by looking at how it affects soil biology. Soil is full of bacteria and fungi and these can break down the cotton fibres, which are polymers of the sugar, glucose. They then use this sugar and we can detect the difference in how much carbon dioxide (CO2) that is produced. This works, because the bacteria respire just like you and me and the more active they are, the more they respire.
Setting up the respirometer
We have a machine that does most of this for us, but first we have to set it up. I thought I’d cover that off in another short video.
We are running the process for eight weeks, which is how long we run our #soilyourundies experiments. We’ve just hit the four week mark and thought we’d check in to see how the experiment was going.
Something expected and unexpected.
The soils activity, which is shown by an increase in respiration, has gone up in response to the addition of the cotton fabrics. This is what we expected, as the soil biology breaks down the cellulose cotton fibres and feeds on the glucose it is made of. So adding cotton to the soil has stimulated the bacterial activity, which is usually seen as a good outcome.
‘None’ is the soil on its own and the difference between the materials and the soil was significant. The unexpected bit was that we did not expect the poly-cotton to increase respiration more than the cottons. Why has this happened? Well right now, we don’t know.
To dye for?
Another aspect of the materials we buried in this experiment is that they contain somewhat different dyes.
The result of this part of the experiment is that again there is a difference (blue and pink were similar, the others were all different), but whether this was due to the dyes or the weave of the cotton is hard to predict. For example, the green is from a drill cotton, so is a heavier more tightly woven material. Our results are adjusted for the weight of the material, but a tighter weave could take more effort by the soil bacteria to break down, thus resulting in the lower level of activity. However, the royal blue colour was present in both a loose weave cotton and a cotton knit and there was no difference between the data from those pots, which might imply that the dye is actually more important than the weave.
So four weeks in we can see that the cotton is stimulating the soil biology, which is great, but we are not sure if the dye is perhaps more important than the weave on the amount of activity we are seeing. This might explain why the poly cotton caused more stimulation of the soil biology than the other cottons, if the dyes in the blue and green colours were perhaps more difficult for the soil biology to break down. One of the things I love about science is that answering one question often leads to others. So now we are thinking about just testing the dyes!
We’ve four weeks to go on this initial experiment, but already this is proving to be a very interesting process. We’ll keep you posted.
Will you run the experiment past 8 weeks if ,say the green dye appears to slow down and prolong the degradation process?
Good question. Not in the respirometer, but we have some other pots going that could go longer. Will wait and see what the next four weeks do.
Interesting and good; respiration is not widely understood. Can you measure or estimate the ratio of C going to the atmosphere vs the amount staying in the soil as resistant Organic C? Do you expect that the C mineralization process may be more valuable?
Nice question Stephen and that is along the lines of where we are heading, hence the comments about methane versus carbon dioxide under less favourable breakdown conditions.
The plan is to look at aggregate stability and soil C, but probably (or rather sadly) not the various Carbon fractions so the amount that becomes recalcitrant will not be determined in these experiments. Would be nice to get a student engaged in this to answer some of these questions.