Douglas Campbell

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since Jun 16, 2015
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Recent posts by Douglas Campbell

Plants have genes encoding a wide range of nutrient uptake transporters.
Each transporter has a characteristic binding affinity for a particular nutrient, and as long as the dissolved concentration of the nutrient is higher than the transporter binding affinity (binding constant), the transporter can bind the nutrient.
Then the uptake can be passive (flowing from high to low concentration), or active (using energy to pull nutrients in against a concentration gradient).

Different plants have different sets of uptake transporter genes, and may have differing intrinsic nutrient requirements to build tissues, and may change the expression of their set of transporters depending upon external conditions.
cheers, Doug Campbell (Ph.D., Plant Science).
1 year ago
Hi - I messed up, this was supposed to be a reply to a fellow asking about earth bag construction in Maine USA.
cheers, Doug
1 year ago
I have lived in 3 conventional houses in New Brunswick, one step north and more coastal than Maine.

The climate is challenging, and builders tend to be cautious.
-~50-60 freeze/thaw cycles per year, so it is difficult to keep masonry intact.  We get 20-24C  (43F?) temperature fluctuations within 24-48 h, multiple times most years
-high precipitation in all forms, often accompanied by driving winds to push water into unexpected places.
-high water tables in many areas
-poor drying potential in most years (this past summer/fall was anomalously dry, although possibly to be expected going forward).

Some comments on ideas from previous posters:
a) Wide eaves can be problematic if the trusses become cold bridges carrying cold back into the ceiling. This leads to condensation and mould if the spots of the ceiling drop below the dew point. Insulation below the trusses, or designs without eaves escape the problem. Ice dams around the roof perimeter can also be problematic.
b) But lack of eaves means problems with drainage around the foundation. Keeping a gutter system running is difficult when it freezes, plugs with ice, then needs to drain rain.
c) Canada guidelines aimed towards an insulated ceiling above a vapour barrier, a ventilated attic and a 'cold' roof for many years. But more recently, for the East, the benefits of a ventilated attic and cold roof are coming into question, and insulation directly under the roof deck, with a warm attic, is being discussed. The idea of the attic ventilation is problematic in high humidity.
d) Thawing out of the ground from the perimeter of the house can create water channels down the outside of any sub-surface structures. Insulation can help.
e) Vapour barriers are very very difficult to get properly installed, and are widely done inadequately. This leads to risks of mould within the building envelope, at the point where a surface reaches the dew point.

Personally I would not consider a construction that relied upon sub-surface living, or hand laid masonry or mortar in my climate. I think it would take great design skill to avoid a mouldy, subsiding mess.
Earth is a poor insulator, particularly when it is water saturated, and heaving up and down.

Some interesting approaches (no personal experience) are insulated slab on or above grade, with proper drainage and vapour barrier below the slab.
Or screw-in metal posts to support a structure above the surface, with insulation below the floor.
Or double-wall framed house with spray foam insulation.
1 year ago
Hi;
If you have an elevation, why not drain to air, rather than to a sump?
A sump is going to be a big electrical draw, compared to running your drains out to air at a lower point.
I would think carefully about multiple layers of insulation that could trap water between them.
Maybe better to have a single layer that can drain above and below.
I would also think carefully about stucco.  If you get any water infiltration between the stucco and the foam, the freeze thaw will peel it off in sheets.
cheers, Doug
1 year ago
Any plant material will eventually compost but pine needles and bark are resinous and slow to decompose.
I have limited experience but perhaps use the pine material to build an outer ring around one of your rain hollows, and cover the bottom of the hollow to retain water, then put better material in the centre of the ring?
Gradually build up piney borders around plantable beds?
1 year ago
This is fascinating.
The sequential ventilation through ever higher levels sounds very interesting.
Two big comments:
Water, and freeze-thaw.

Have you spent a winter/spring/fall on PEI?
They currently get about 50 freeze-thaw cycles per year, depending upon location.  Temperature can fluctuate 20C in 24 h (-10C to +10C is common; -25C to +15C happens).
So any sort of masonry related structure (10% cement to stabilize bags) is very prone to cracking, heaving, crumbling etc.).
There is a good reason why a bunch of Scottish settlers abandoned stone houses within 1 generation.

And related, drainage?  A hole 15' deep on PEI is going to be well below the water table in most places.  I fear your structure will be a pool.
I think many of the earth dome/earthship/earth cone ideas are coming from much drier places.

Building practices in the maritimes are conservative, partly because conditions are so inimical to experimentation.
If I ever build another structure in the region it will be on an insulated slab, completely above ground, which is a practice starting to spread.
I have friends nearby who have a straw bale house on a slab with wide eaves for rain shedding.
cheers, Doug
1 year ago
This is a very big topic.
To continue from Lindsey:

-Instantaneous light level
 Full sunlight on a cloudless day at noon is about 2000 umol photons m-2 s-1.  That level is higher than the level to saturate photosynthesis for most leaves.  Most leaves, even leaves on plants in high sunlight, are light saturated by around 500 umol photons m-2 s-1.
  A greenhouse would cut this by about 50%, so maximum level in a greenhouse is likely around 1000 umol photons m-2 s-1, maybe a bit more with careful cleaning, materials and design.  1000 umol photons m-2 s-1 is still more than enough to saturate leaf photosynthesis for most species.

 But leaves do not lie flat on the ground, they have an orientation and are usually in a canopy of other leaves that lowers the instantaneous light.
 (Also, humans have a logarithmic response to light; typical room light is ~40 umol photons m-2 s-1, 1/50 the level of full sunlight.  So it is tricky for us to gauge light levels.)
  Exposing a leaf to light above its saturation level often leads to photoinhibition; a decline in photosynthesis or growth rate caused by excess light, which has toxic effects.  In most cases it is not the absolute level of light, it is whether light is above or below saturation.  The saturation level varies with species, developmental history, temperature, nutrient status and prior light acclimation; most leaves have some capacity to acclimate over time to changing light.
  And, saturation of leaf level photosynthesis is not the same as light saturation of growth, nor of production of the desired crop.  Growth usually  light saturates at levels below leave light saturation.

-Photoperiod
  The length of the light exposure in the day.  Plants have many photoreceptors aside from the photosynthetic system, and some are sensitive to very low levels of specific light.  Some plants are able to exploit long photoperiods (tomatoes in Alaska etc.); others are not, and some respond to changing photoperiod to complete their developmental cycle.
  Depending upon species light acclimation can flatten the response of growth to photoperiod somewhat; long low light photoperiods can sometimes drive growth at a rate similar to higher light shorter photoperiods.

-Spectrum
 The colour of the light has regulatory effects upon the photoreceptors, with different plants responding differently.  Some wavelengths (UVB) are strongly inhibitory.

-Photon dose
  Total photons m-2  in a given period.  This can be a factor; it is the product of instantaneous light and photoperiod (actually the integral of instantaneous light over photoperiod).  Think of a laser flash that delivered a whole days light in a ms; the plant would be incinerated.  Then think of a very dim light for a very long time; the plant is unable to grow at all because the light level is insufficient to drive net photosynthesis, so no matter how much total light is delivered slowly there is no growth.  The useful photon dose also interacts with nutrient status, temperature, presence of mycorhizae, species, developmental history etc.

-UVB & UVA effects are complicated, dose and species specific.

sunnily yours, Doug Campbell (Canada Research Chair in Phytoplankton Ecophysiology, Mount Allison University)
2 years ago
Humanity is systematically accelerating the flux of mineral nutrients from land to ocean.
So crab meal and and other marine byproducts onto agricultural land are a tiny step against the main flows.
2 years ago
I am next door in New Brunswick.
I think these are 'wild raisin', Viburnum nudum, or another Viburnum.

They are edible, and some people rave about them, but I do not bother picking them.  They ripen purple, and shrivel into raisins on the shrub.

'Dogwood' is usually used around here for species of Cornus shrubs.  Cornus always has distinctive curved veins along the long axis of the leaf.
Local names are confusing.
2 years ago