Monday, September 20, 2010
A Bioneer's Greenhouse Part 4 - Soil
So now I have talked about how I am going to lay it out and how I am going to get water into and out of the greenhouse. Next I am going to have to have something to grow all that wonderful produce in, some sort of wonderful soil. Now, I could just buy a load of topsoil and hit the ground running. But that would be cheating. For someone who engineers with biology, the soil is by baseline, my starting point, my most important factor. Yes, I need good, fertile soil. But more importantly, I need living soil. For that, I want soil that is almost 100% compost.
I am fortunate to live in the neighborhood I live in. I have a nearly inexhaustible supply of organic material right out my back door. The ecology of my back yard is chaparral, a dry, scrubby landscape dominated by scrub oak. And yes, scrub oak really is oak. It stays small and twiggy and is easily chipped up in my little electric wood chipper. It also grows really densely. I could go out daily and maintain trails, reduce fire danger by removing brush that’s too close to houses, and take it from dense patches. Then I bring the trimmings back to the house and chip them up. Between the sheer amount of scrub oak and how fast it grows, I doubt anyone would ever notice that it was gone. And those that did would probably appreciate my maintenance work. I certainly wouldn’t be clear-cutting anything.
Once home, the chips would be pasteurized and inoculated with culinary mushrooms. Many of the best culinary mushrooms really grow well on oak. So I could grow some in pots or even in the beds themselves. If I can get several blocks completely inoculated with mushroom mycelium, I could create a bed with fresh chips and then break up the blocks and use them to inoculate the bed. With any luck, I would have many pounds of tasty mushrooms as the first crop from my garden. When the mushrooms have gotten what they want out of the wood chips, they get fed to the worms, who will finish them off to make high quality compost in just a month or two.
Now, I have to say that the prospect of harvesting and chipping about 10 cubic yards of scrub oak is seriously daunting. Fortunately, I have a few cheats that allow me to get a quick start. First of all, there is straw. It is a little less dense than wood chips, but it is also readily consumed by a wide variety of culinary mushrooms. A bale is only about $4, so I can get them in bulk pretty easily. So that will probably be my starter method. For my second cheat, I have another readily available resource. During monsoon season, my neighbors and the neighborhood in general spend a considerable effort cutting and removing weeds, especially tumbleweeds. I can just walk around the neighborhood pulling weeds. The green matter will help with the composting as well as improve the nitrogen content of the soil. The best part is that I can use all weeds, regardless of whether they have gone to seed or not. As the raw materials compost, the level of the top of the beds will drop considerably, which means that I will have to keep adding more and more material until the decomposition has slowed down. Assuming I fill it with weeds fairly early in the process, any seeds in the mix will end up so far underground that they will have no chance of pushing to the surface once they sprout.
Once I have gotten the beds a little over half full, I need to start paying attention to the makeup of the soil. I will test it and start looking for amendments. Most of the best soil in the world has one thing in common: it contains large quantities of mechanically weathered rock. The fine rock particles have lots of minerals in them that are readily available to plants. They also have good staying power in the soil. So I will do a lot of looking around at this point and see if I can find a good source of greensand and rock phosphate to supply the potassium and phosphorus I need in my soil. I don’t know of a good rock-based source of nitrogen, so I will probably have to get some blood meal. I will certainly be using lots of compost, which should help. I have some friends with chickens, too, so chicken manure will be added. I will also have to start taking drainage into account around this time. If my soil doesn’t drain well, I will start adding sand or pea gravel to the mix. If it drains too well, I might just add a little unused clumping kitty litter, which will help plug some of the holes and retain water. Clumping kitty litter is made from expansive clay. Caution is recommended with this method, though, as a little goes a long way.
Once I have a fairly decent level of soil that has composted well enough to support plants, I can also plant green manures. Something like alfalfa or hairy vetch would add lots of nitrogen to the soil. I could also begin selectively planting food crops at this point. The greywater distribution system would probably not be fully buried in the soil yet, so any crops that grow food on the ground or in the ground, like zucchini or carrots would be out. However, crops like corn, sunflowers and pole beans that raise their crops well above ground would be a good choice. In addition, these crops produce lots of compost when they are done.
Eventually the final soil level will be reached and will be fairly stable. I fully expect this to take 2-3 years at least. It isn’t until this point that I can consider planting perennials. Any time before that the constant sinking soil level and constant addition of more mulch and compost would be death to anything that would be around a long time.