I’ve found a layer of plow pan and have to integrate it into my
water harvesting design, or destroy it. I’ll explain the situation. This is a brainstorm and question thing:
I’m in Tucson, home of
Brad Lancaster Rainwater Harvesting techniques. I’ve gone through his
books, but haven’t seen what I’m dealing with. Perhaps there is some wisdom and
experience to be found here.
I have moved onto, what I have heard, was an arugula farm, probably 50 to 70 years ago. It has been urban residential since. We set posts for a wall around the ¼ acre property and found a consistent layer of compacted soil, about 6 to 10 inches deep. It is obviously plow pan compaction, about two or three inches thick. It isn’t
concrete or caliche, but it does require the caliche bar and the extra effort to dig through. It definitely slows the penetration of water.
The lot is flat and previously irrigated. We dug up some old terra cotta pipe, long ago used for irrigation. The soil around here is rich, once river shed before the river was pumped dry.
I’ll soon have a weekly community, the Tucson Family Sweat Alliance (a non-profit) meeting coming to my home and my place is to provide a peaceful garden atmosphere for it.
I intend to soon, break up the blank flat lot with a backhoe, into a more interesting rise and fall, using swales, basins and harvesting rain.
I have a blank dirt canvas right now. There is a large eucalyptus tree in the center of the property next to a patio. There are three other
trees that were dwarfed by neglect, but are coming back. It will need more shade, trees…Tucson. The existing trees are housed in holes lined with that circular concrete block.
I have ample information from Mr. Lancaster’s information to do his thing, but this layer of compaction has me thinking. Normally, in a wetter climate, it would cause
root rot and keeping soil dry is the problem. Different in this desert, the moister percolates out of soil at an amazing rate.
The coming plants to live there are with lesser root systems and adapted to shallow moister and infrequent rains. The trees need a deeper penetration. The basins around the trees can gather all of the rainwater that comes its way, creating ponding that will seep deep quickly
enough. My experimenting (digging a slight basin and watching what rain does to it) so far showed me the
local grass and weeds loved the situation. The collected rain sank away within 24 Hours.
This is to be other than my personal veggie garden.
The trees need a deeper watering. I had intended to create the basins about 8 or 10 inches deep, but that leaves probably the pan layer of compaction bared, perfectly, like a soft bedrock. I’ll mulch it and plant flowering, scented desert bushes such as sages in those basins, but am I wasting water by allowing the penetration to slow and not water the deeper
roots as effectively?
I’m considering leaving ruts and holes in the hard surface to help seepage for the trees, but not break up the whole of the plow pan. This, in order to retain the desert type soil and drainage systems for the desert plants, which take shallow solid strata just fine. I've thought to poke a hole in the pan for a tap root for each bush.
Lancaster often does use hard rocks to line his basins, preventing erosion. Perhaps my partial breaking of the compacted strata would effectively be similar.
Who has experience with plow pans in the arid desert? Any thoughts, or opinions on this, before I destroy a possibly useful destroy a water retention resource that can’t be repaired?
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