Dew as a water source?

[garand555]

After the weedpocalypse I had last year, I decided to plant some cereal rye and hairy vetch last fall as a means of weed control.  In large swaths of this stuff, the rabbits found a food source this winter, and my little terrorist (Great Dane pup) isn't old enough to ward them off yet, so a lot of it got trimmed back to the ground and some of it was even killed.  The parts that weren't hit are probably ~18" tall now, and that means a lot of surface area.  What I noticed a few days ago, at about 7:30 in the morning, is that dew had collected on the plants and was dripping off of them onto the soil, and even without watering, the soil surface is perpetually wet.  The parts that were knocked back by the bunnies need irrigation to catch up, and the parts that are doing well need none.  This could be because of the dew, or it could simply be the result of a more extensive root system.  Or it could be a combination of the two.  

I have only found two studies thus far on the effects of dew in this way.  One consisted of a guy who recorded the number of days that his shoes were wet when he walked through the grass on mornings where there had been no rain.  That went into the circular filing cabinet.  The other used radioisotopes to track how much water was used where.


The role of dew in the Negev Desert

Using a two-source isotope mixing model, we found that S. inermis, A. sieberi and H. scoparium used, on average, 56, 63 and 46 % of their water from dewfall, respectively. Our results suggest that dew-water utilization by Negev Desert plants is highly significant ecologically and thus may be more common than previously thought.

My annual average precipitation is 8.5"-9" per year, making water something always on my mind.  I'm thinking that I need to get a quality soil moisture meter, and start measuring things to quantify the effects of this, but it looks like having a high above ground surface area cover crop in the early spring might be a huge advantage for soil moisture in my area, beyond the effects of just shade lowering evaporation rates.  There does not seem to be a lot of research on this, though I haven't searched every nook and cranny of the internet.  

[diane]

Is the dew coming from your plants, so that they are recycling water all on their own?

I have been in places where the plants receive their water from fog -along the coasts of Namibia and Chile. Also in the Andes between Chile and Argentina there was a large structure on which fog would condense and drip down to collectors on the ground below.

[garand555]

Mar 24, 2017 12:02:37 GMT -5 diane said:

Is the dew coming from your plants, so that they are recycling water all on their own?

I don't know.  I need to start taking physical measurements, and even then, without doing an isotopic analysis or something of the sort to determine the source of the moisture, it will be difficult for me to say one way or another if the moisture is being recycled, or is coming out of the air, or a combination.  Even if it is just recycling the moisture from transpiration, that is something.  There just doesn't seem to be a lot of research into this.  It seems like it would be an important thing to understand for those of us in arid regions.  

[steev]

There is/was a product called "Earthboxes" promoted as a way to nurture trees in deserts by harvesting dew.

I just checked that name; either I've mis-remembered or that has morphed into a different product.

[diane]

You should be able to do an experiment to see whether the water is coming from the soil directly or via the plants' transpiration.

See if a piece of hard plastic suspended at leaf-height over a bare area of soil has dew condensing on it as much as the plants do.

You could get fancier and somehow measure the amount of dew per square centimetre of leaf or plastic, but just eyeballing it should give you a useful idea.

[philagardener]

Mar 24, 2017 12:19:09 GMT -5 steev said:

There is/was a product called "Earthboxes" promoted as a way to nurture trees in deserts by harvesting dew.

I just checked that name; either I've mis-remembered or that has morphed into a different product.

steev , you might be thinking of  is a company called Dew Harvest that offers a product called the Groasis Waterboxx but it is mostly a capillary reservoir than a true fog collector.

Here's a cool blog post from Columbia researchers about the fog harvesting that diane mentioned.

[steev]

That "Dew Harvest" is somewhat the same idea; the one I vaguely remember was promoted by some European as a way to facilitate tree-planting around the Sahara.

[cynic]

In the UK there was an old technology called "Dew Ponds" - sadly not used much anymore since the farmers prefer to use electric pumps.

en.wikipedia.org/wiki/Dew_pond

Maybe this or a variation on it could work in your situation.