How do I remediate shallow clay soil over bedrock in residential compound?

Discussion in 'Planting, growing, nurturing Plants' started by tresenglish, May 22, 2015.

  1. tresenglish

    tresenglish Junior Member

    Joined:
    Dec 5, 2012
    Messages:
    7
    Likes Received:
    0
    Trophy Points:
    0
    I own a small apartment complex (two triplexes) with a common yard. I want to create a food forest that shades several common areas. And I want to use graywater and harvested rainwater to provide most irrigation. I plan approximately 10 large basins around the property to capture runoff from 10 different roof segments (total basin area about 350SM). The soil is almost devoid of organic matter. The climate is semi-arid (≈275mm) and hot (42C) with occasional hard freezes (-8C)

    The problem is that the site has a shallow, heavy clay soil (≈1m) on top of solid rock (calcium carbonate called caliche). And if I use all the water I have available - I will have too much water and will experience severe water logging.

    I think I have to remediate the soil, but I can't afford to simply replace it or even amend it with large amounts of sand. And the site is currently occupied, so major excavation is not an option, even if it was affordable.

    Questions:
    * Can I use a combination of deep-rooted grasses (or other plants) and legumes to break up the soil and add large amounts of organic matter to allow the soil to drain better?
    * Since it can't drain down, should I build some sort of French Drain around the edge to carry away the water from the basins. If so, what approach would you recommend?

    I would greatly appreciate any suggestions you have. I was already into this project before I realized that the severe drainage problems mean I have too much water, not too little. (I can't really control the water. I get how ever much I get when it rains, and I can't control it. My only alternative would be to forgo the rainfall.)
     
  2. 9anda1f

    9anda1f Administrator Staff Member

    Joined:
    Jul 10, 2006
    Messages:
    3,046
    Likes Received:
    199
    Trophy Points:
    63
    Gender:
    Male
    Location:
    E Washington, USA
    Climate:
    Semi-Arid Shrub Steppe (BsK)
    Hard to think that one could have too much water with an annual precip of only 275mm!
    Your thoughts of green manure plantings will help begin to build a layer of organic material over the clay soil your yard sorely needs. Once you have your trees established (with associated understory), you will have a somewhat self-mulching system to continue building soil. Do you have earthworms in that clay?

    I've found here that punching through the caliche enables drainage and provides access for tree roots to a vast layer of moist "dirt" beneath the caliche layer. By renting an electric jack hammer for a day, I can easily punch through the caliche and also get the benefit of large white caliche chunks for border stones. Perhaps a better option than the time/expense of a curtain drain.
    More info: https://ag.arizona.edu/pubs/garden/az1281/

    Are your tenants cooperative enough to contribute kitchen scraps to a compost/worm bin? This can be very unobtrusive and help contribute high-quality organic materials to your project.
     
  3. tresenglish

    tresenglish Junior Member

    Joined:
    Dec 5, 2012
    Messages:
    7
    Likes Received:
    0
    Trophy Points:
    0
    Thanks for the local reference, Bill. I will check with the local authors.

    Unfortunately, the caliche is at least 6' thick. (I say "at least", because we stopped digging at 8') No punching thru this with a jackhammer. I just dug some test holes for lateral percolation tests, and the clay layer is 26".

    Obviously, improving the soil is good. Will it help me drain the soil so plants don't get waterlogged?

    The reason for the water logging threat is that I want to concentrate roof runoff into basins that also receive graywater. The total of rain, water harvesting, laundry, and evap cooler bleedoff water is 63,000 gallons, and the cumulative basin size (in 10 basins) is about 3000 SF. This would be great, except that the three graywater basins will be at field capacity during our winter rains and could become saturated for several months each winter. (We have two rain seasons, summer and winter.)

    I am trying to head this off by increasing lateral percolation, to get water away from the basins (without loosing it). I can't legally just dump the water, because the basins will receive graywater, which has to be retained on site.
     
  4. songbird

    songbird Senior Member

    Joined:
    Sep 12, 2013
    Messages:
    1,780
    Likes Received:
    142
    Trophy Points:
    63
    Occupation:
    gardening, reading, etc
    Location:
    near St. Charles, MI, USoA
    Home Page:
    Climate:
    -15C-35C, 10cm rain/mo, clay, full sun, K-G Dfa=x=Dfb
    does your local area regulate graywater systems? that would be where you'd have to start.

    it sounds like the area is very unsuited for such a system. you might be able to use a small amount of the gray water but i think you'd need a reed bed or some other treatment area before wanting to use the water in any gardens. there's a lot of gunk in laundry water, some of it isn't biodegradeable (plastic based fabrics) and some of it is harmful and can't be used directly. because your drainage is so limited any mistakes would be very noticeable for a long time and people will notice it because it will smell.

    french drains only make sense if they have outlets, in your case i'd suspect they'd end up as conduits for gray water...
     
  5. Bryant RedHawk

    Bryant RedHawk Junior Member

    Joined:
    Sep 8, 2014
    Messages:
    607
    Likes Received:
    83
    Trophy Points:
    28
    Gender:
    Male
    Occupation:
    Arkansas Senior Appraiser
    Location:
    Vilonia, Arkansas, deep in the woods
    Climate:
    USDA zone 7b,8a.
    Sand is not going to be a good amendment for your clay soil, it will turn it into concrete. Deep rooting plants and perhaps some daikon radish will do far better at building soil for you.
    Caliche is soluble with acids such as acetic (vinegar) this is a good thing to know since if you were to chip out holes and pour in a gallon of vinegar to each hole, you would end up with some porosity which would continue to increase as water infiltrated to that layer and rewets the stone.

    It sounds like you have built 8' deep basins for water catchment, is that the case? if it is then your 26" clay layer isn't going to move any water that sits below the layer.

    Bill gave you a good link and you will have to do the research so you can find out what is allowed and also feasible for you.
     
  6. DC Brown

    DC Brown Junior Member

    Joined:
    Apr 29, 2015
    Messages:
    40
    Likes Received:
    10
    Trophy Points:
    8
    I can only speak of my own experiences and research with regards to clay. My clay is yellow ultic clay, and is amendable with angular sand - but not porous sand e.g. pumice and scoria. The porous substrates allow for clay platelets to fill the spaces and where they bond with external clay - the concrete mentioned previously. One big culprit is dolomite lime. The Mg in dolomite is too high for typical plant consumption and so it builds up in the soil, bonds across clay sites, and makes hardpan. Gypsum is problematic too unless your clay is sodic (high sodium). I use 20% gypsum and 80% oystershell, then after that, no more gypsum.

    I can literally melt my clay, it gets gooey like a gel within weeks and becomes soil in a couple of seasons. My neighbors are lined up for my 'product' to do this. It's a cost intensive, but one off, mix.

    Compost - good compost, add as much castings as you can get to it. Coverage at least 10L/m2.
    Cococoir - this takes about 4 years to break down - peat/leaf duff disappear in a season. At least 5L/m2.
    Gypsum - 20% recommended dose. Oystershell - the other 80%
    Di-calcium phosphate - doesn't interfere with mycorrhizae used properly, crush the pellets to dust and add at 30gm/m2.
    Rockdust - As recommended. Seaweed - as for rockdust - minerals... + hormones, growth promoters and more.
    Sheep pellets or blood and bone meal - this is the nitrogen to compensate for the high C coco-coir. Also to feed the microbes in the compost.

    Edit - and sand! About 10L/m2.

    Till this in adding as much compost as you can spare, put a mulch layer on top even better. Then plant with plants suited to the task.

    Clover - fixes N, holds soil together, cheap and easy. Beets and beet greens - well adapted to hard clay, can be planted tightly for a lot of biomass below ground fast. Mustard - this will detox and develop soil. Oats - binds and aggregates soil structure, feeds chooks :D There will be many others but these are the 'volunteers' I see a lot, and various other weeds I should know by now. Borage will also take wherever it is rich, indicating planting sites for hungrier veggies.

    Hope it helps.
     

Share This Page

-->