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About that dry dirt...

1K views 6 replies 7 participants last post by  Berkeley Mike 
#1 ·
Hey all, I told my org I would write up a little blog post to answer the question, "why aren't we digging?". I'm looking for a little education material to quote/reference/paraphrase that explains why digging in bone dry dirt doesn't work, and the importance of waiting until the fall rains begins.

Any help would be appreciated.

Thanks!!
 
#2 ·
Around here, you can dig when it's bone dry (if you can swing a pick axe) . . . you just can't shape and pack anything. (I'm thinking in particular berms, rollers, jumps, etc.) If people are willing to haul 5 gallon buckets of water from a nearby creek (like dozens of them, not just 2 buckets), then you can build.

But, yeah, I like waiting for perfect damp dirt too.
 
#3 ·
Another issue is that the dirt is so dry it's hydrophobic. Because it's hydrophobic, it can't compact and will either blow away in the wind or wash away in the first rainstorm.

It's hard to believe, but it's been so dry here in Seattle that when working on my pump track literally the water just beads up and runs off unless you just mist it over and over again. When there's enough water going, of course it just takes soil with it.

I don't have a primary reference for hydrophobic soil, but here's Cliff Mass, a meteorologist at UW:

Finally, there are other issues. It is far better to water less frequently but with greater amounts of water, an approach that fosters deeper penetration of the water into the soil. And often the best times to water is AFTER IT RAINS. No, I am not crazy. Very dry soil can become hydrophobic, meaning it does not readily absorb water. Thus, a light watering might stay on the surface without getting to the roots. After an extended light rain, the soil can start moistening, opening the pathways of water into the soil. And watering after it rains, promotes deeper penetration of water into the soil.
From: Cliff Mass Weather Blog: How to Reduce Water Waste from Sprinklers: The Science of Spray
 
#4 ·
I don't have any reference material advising against building in dry conditions just anecdotes and experience. As others have said, a trail can't be built properly without soil compaction and that won't happen with dry soil. In our neck of the woods, digging in dry dirt is physically harder (lots of clay) and can be demoralizing for volunteers. We've done emergency repairs during drought conditions by hauling in water to wet/compact the soil but unless the water is allowed to soak into the dirt for a a couple of hours it becomes a sloppy mud that is nearly impossible to work with.
 
#5 ·
As far as soil moisture goes, do a search on Field Capacity and Saturated Soil.
Water moves through macropores using gravity, while micropores rely on capillary action to pull water in. Once the micropores dry out it can be difficult to rewet the soil. It has to be done slowly.

There are products out there to help. These are surfactants which lower the surface tension of the water and allow it to penetrate micropores. Most are made from corn cobbs.


If someone is telling you not to dig because the soil is dry and too hard then maybe they are using the wrong tools. Grab a pick axe and a spud bar.
 
#7 ·
"The Howitat do not carry water!"

Anthony Quinn as Auda abu Tayi
Lawrence of Arabia, 1962

We have had drought conditions here in California. We still move dirt but only because we have to take advantage of manpower when it avails itself. No, it is not optimal but 800 man-hours of dirt moving is hard to turn down.

Yes, we would like to bed-in our work and our projects over the last 3 years have suffered but when it does rain we have different work to do.
 
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