It's been a while since I've taken the time to sit under a tree at the campground, but its good to be back. I was moved to post today because I was reading my soils textbook, The Nature and Properties of Soils by Nyle C. Brady and Ray R. Weil. It is a thick book and about as dry as an Aridisol, but I read the section about soil conservation and the section about soil chemical pollution.
Well, soil erosion is a huge problem in our country. Not only is it a bummer because we're losing precious soil, but also because it affects water quality. There are many factors that affect rates of soil loss and just as many ways to fix it, but why don't I give you an example of what it looks like in my own backyard in Montpelier.
There is a rill forming on the slope at the bottom of out driveway. The rill starts at a sudden drop off at the end of our mowed yard. The sudden drop off here has created an increase in the velocity of the water and thus increases the ability of the water to pick up and hold sediment. The kinetic energy of the water has torn apart this hill in several rills that expand from year to year, depositing bare mineral soil on top of the leaf litter in the forest below and exposing rock that was previously hidden inside the soil.
My brother and I filled the slope with debris from the forest to try and slow the water down. When the water in the rill slows down, it loses its ability to hold sediment so it deposits sediment on the sides of the sticks and stones we used as debris. At least that is the idea. We also constructed little temporary dams out of grass and sticks, that should allow water to flow through but stop some sediment. Also our treatment may be flawed simply because when an equal volume of water is forced through a smaller opening it actually speeds up. Oh well, we'll see if it hurts or helps.
Now I have a new plan to stop this erosion. And it is a really good idea if I do say so myself. My textbook said that 60% of soil loss prevention has been due to government plans of letting agricultural land be fallow rather than farmed. If land grew back into grassland it was worth a certain amount to the farmers and if it grew into forest it was worth even more. People were paid to NOT work! Well this leasing system may still be going on today, but I have doubts about its effectiveness on a global scale, If we aren't growing crops in our own country, they are being grown somewhere else, and what regulations on soil losses do they have in Mexico, the Carribean? Anyway, on the backyard scale it makes perfect sense, because the yard isn't used for production. If it is allowed to grow into a grassland or even a forest, the benefits could be amazing.
Benefits:
1. Global warming
2. Biodiversity
3. soil loss reduction
Letting the yard grow saves lawnmower gasoline while sequestering carbon in plant biomass to fight global warming. As plants photosynthesize, they take CO2 from the atmosphere and use it to maintain their metabolism as well as to build their physical structures, forests sequester much more biomass than grassland, but either one is better than a mowed lawn. The reason why tall grass or wild grass sequesters more carbon than a mowed lawn is because grasses maintain a balance between their leaves and their roots. Say you've let your grass grown to be six inches tall and then mow it, the grasses new leaf length of 2 inches cannot sustain the mass of roots that it did at six inches because its photosynthesis potential was cut down to one third. The grass will self-prune its roots under the soil, almost like a root mower is following behind your real lawnmower. If the leaves are allowed to grow, so are the roots which also stabilize soil.
I propose to let two areas of the yard grow wild. The first is the area directly above the rills, it is a shallow slope, maybe 5% and it is already covered in short grass. If it was allowed to grow, the grass would create a heavier root mass due to greater biomass above ground. It would have biodiversity increases as well, with wildflowers and insects having more prevalence there. The hardy stems of tall grass would slow the velocity of water even more than the flimsy short leaves that are there currently. The area would have improved cover for rodents, who need to stay hidden in order to not get et up by big ol' birds. When the insects and rodents dig holes in the soil, it increases water infiltration rates, so less water will actually reach the rill.
Furthermore, more leaf area over the soil in this spot will increase the interception of precipitation as it is falling, this means that the water slows down on its descent to earth, giving it more time to evaporate before hitting soil. This interception has been shown to reduce inputs of water into a system, which is just what we want here.
The other part of the yard that I propose be left uncut is what I believe to be a significant source of water collection contributing to the problem. Uphill from the driveway there is a strip of very steep terrain, maybe 50% slope. It is mowed every month or so by a special lawn mower guy named Jackson who specializes in steep slope mowing, good conversation, and wearing shorts all the time. This slope is a strip between the road and our driveway that covers perhaps a half acre. A quarter of this area is probably contributing water to this rill problem that we have. If this wedge of land were left unmowed, it would have all the same effects as above, but rather than trying to slow water down after it is already moving fast, it will attempt to reduce water inputs in terms of quantity and velocity.
Again more grass will promote soil infiltration capacity, and the interception will decrease overland flow in general. Because even during a rainstorm, the rain drops are evaporating as they fall and while they sit on the ground or on leaves.
The other important way this treatment will help is that in the spring when there are seasonal flows of water from melting snow, there will still be the dead stalks of tall grasses and wildflowers to promote evaporation and sublimation and reduce water velocity.
Perhaps you should consider a treatment like this in your own yard. Consider the carbon sequestration along with the reduction of gasoline consumption. That alone could make a big difference. I think it is a very reasonable thing to let part of your lawn go wild and see how you like it. Heck, maybe next year you'll sell your lawnmower. And if enough people do what i suggest, maybe it will offset the electricity consumption of the computers we used to talk about it.
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2 comments:
Very interesting ideas,Adam.
I'd be interested in watching the driveway to see what the water does. I suspect that most of the water that runs downhill from the driveway comes from the road, not from the bank, but it's hard to say. It might be worth putting some dye on the ground and seeing where it goes.
As you know, the driveway is blacktop. I've seen some driveway tiles or bricks, I guess you would call them, that are designed to be open, so grass can grow through the openings and, naturally, water can soak in rather than running off. I recall when we were looking at them years ago that they seemed pretty expensive, but this seems like something worth looking into for whenever we need to repave the driveway.
What do you think about creating a swale along the bottom of the bank? I think if we did that we could direct the water away from the driveway and down toward the yard, where it wouldn't run off.
I'll be interested in seeing what happens to the bank where you and John built up the dams.
There is another question: aside from the fact that the erosion removes some of our side yard, is there any harm to the environment to have this erosion, given that the dirt is just going downhill into the woods?
I am in the middle of reading The Omnivore's Dilemma (an excellent read, which I heartily recommend), and though the author is a writer/journalist specializing in food and agriculture (read, not a soil scientist), he raises some ideas which contradicts certain things you've assumed. I hope I can paraphrase the content appropriately.
"If we aren't growing crops in our own country, they are being grown somewhere else"
This is not necessarily true. Our national government's policy for the last several decades intentionally supports industrial production of corn (mostly) and soybeans (secondarily), attempting to maximize the yield per acre in an unsustainable monoculture. Our government subsidizes farmers to do this. It is possible only because it is currently economically feasible to spend 10 calories of fossil fuel to create 1 calorie of corn. This cheap source of corn means that cows can be kept in small feedlots instead of open range and fed corn rather than grass, even though the cow's rumen isn't adapted to this diet and consequently needs a lot of antibiotics.
This cheap corn is also used to create fillers, stabilizers, sweeteners, and the incomprehensible host of ingredients that you see on the side of packages (MSG, guar gum, etc.).
Why do we do this? Because it is an economic engine that gives our country incredible political power.
If we lower the production of this corn, we aren't necessarily taking food out of someone else's mouth. We are merely managing the price of a commodity (i.e. corn).
"If it was allowed to grow, the grass would create a heavier root mass due to greater biomass above ground. It would have biodiversity increases as well, with wildflowers and insects having more prevalence there. The hardy stems of tall grass would slow the velocity of water even more than the flimsy short leaves that are there currently."
Not so fast. Grass has a life cycle that evolved along with fire and ruminant animals that regularly cropped it short. True, cropping the grass (or mowing it) does kill off root mass BUT that root mass is a MAJOR player in soil regeneration. Those roots were made out of carbon pulled from the atmosphere. When they die and compost, they bcome NEW soil that wasn't there before. So cropping grass actually encourages soil regeneration.
If you let the grass grow, it will eventually reach its maximum height and the stems will become thicker and woodier. The grass is no longer actively growing so it is pulling less carbon from the air and less water from the soil. There is an equation that has to be balanced here.
A better strategy to prevent soil erosion might be to regularly crop the grass at the peak of its growth curve and let it regenerate. I'm this isn't so neat and tidy as I suggest. You would have to let the grass grow taller than a lawn mower could handle. And a lawn mower doesn't fertile the soil behind it as a buffalo would.
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