The other technology was a very interesting type of greenhouse utilizing combined fertilizer and irrigation techniques. Each Greenhouse is roughly 9,700 square feet and costs just $3,200 US to build. It has a natural dirt floor and is oriented east to west with the brick wall on the right being the north. The brick wall is a full three feet thick. It is faced with a single layer of brick, and behind that is an earthen berm. This serves two purposes, one very little sunlight enters through that side, and it is far more durable than the plastic. More importantly though, it is a massive heat sink. There is no heating in these structures, and the plastic sheeting on the south face is just one layer or perhaps 3 or 4 mm clear plastic. All day during the winter the low sun shines on the wall and heats the brick, and the dirt behind it. As the temperature drops at night, the heat migrates out of the wall, heating the greenhouse.
The end walls are brick as well, with a small end house on one side. They feature a single layer of brick on the outside, a layer of 4″ Styrofoam insulation faced with a layer of skimcoat cement with fiberglass pieces in to to help hold it together. The bottom and top 2 feet of plastic along the south face wrap around a rod to provide passive ventilation when it is warm enough. These areas however are covered with an incredibly fine screen to keeps pests out. This one didn’t have it, but the others had large yellow sticky traps suspended form the ceiling to catch any insects that did get it.
Every four houses has a pump in a small manhole outside where they all meet. In each house there is a 30 or so gallon barrel filled with liquid fertilizer, a hose that goes down into that barrel, and a simple venturi system is set up to suck fertilizer out of the barrel when the irrigation is happening. Each set of two rows of plants has a VERY thin layer of plastic over it with small holes torn in it for the plant, and between the pair of rows and the next is a shallow (4″) ditch. Drip irrigation is used under the plastic that covers each pair of rows of plants, keeping the moisture in the ground and not in the air.
It gets cold here, and these greenhouses are built for year round operation. With just a single layer of plastic there is virtually no insulation from that. On the outside there are a series of overlapping 8 foot wide blankets that are rolled on a pipe. In the center of the pipe is a motor fixed to a pole with a hinge in the middle. Turn a switch and the blankets all roll down. Turn it the other way, and they all roll up. Notice the one in the back with the blankets all the way down. At first glance this system seemed very rudimentary After really spending time with it however it seemed ingenious. Simple, cheap, reduces water (the limiting factor here for growing) by 2/3, reduces insect, fungus and bacteria pressure and extends a growing season from around 180 days to 365 without the need for heating. This was a demonstration facility (although they had 120 of these greenhouses and where building 200 more) so they were all built with good materials. The farmers in the area build them smaller (each of these were 30% larger than their farms) and many used 100% dirt (no brick) in the north, east and west walls; used blankets made from woven corn and rice stalks; and used cheaper plastic on the south wall (1.5-2 mm). Most farmers build them for around 8,000 RMB or 1,280 US$ (half what the demonstration center builds them for).
