We've been inspired by Fan Sheng-chih Shu. His writings from the first century BC describe a method of irrigation where a unglazed clay pot is buried in the soil. When filled with water the clay pot turns into an amazing high-tech device. The micro-pores of the clay pot allows water to seep into the surrounding soil. A key characteristic is that the water seepage is regulated by the water needs of any nearby plant. When the plant's water demands have been fulfilled and the soil is moist, the water seepage from the clay pot will stop. When the soil becomes dry, water seepage will begin again. This seepage is controlled by soil moisture tension. It's automatic irrigation without timers or electronic sensors!
Water Efficiency Combined with Liquid Fertilizer
Some designs (see below) allow you to bury the olla in the soil or potting mix. This allows the delivery of water directly to the plant's roots. No water is wasted. This is excellent for arid climates like in many parts of Africa. Finally, you may supply the olla with water mixed with liquid fertilizer. You'll only need about 1/4 to 1/2 of the fertilizer you would normally use. Although liquid fertilizer is more expensive than granular, it may end up costing less because of the tremendous efficiency of the delivery of the fertilizer directly to the plant's roots.
Combining Ollas with Global Buckets
Only one bucket is required and the use of power tools for drilling and cutting of buckets is eliminated. It's much more fun to caulk (required for clay pots) than to drill. We've begun (summer 2010) the testing of ollas in Global Buckets. So far we've had excellent results.
How to build your own Olla Global Bucket system:
Step 1: Build the clay pot. It's easy! Just glue two unglazed flower pots together.
Step 2: Bury your clay pot into a bucket with just the top of the clay pot exposed. Use potting mix with dolomite.
Step 3: Keep the clay pot filled with water. After a month of hand watering (boring!), we're designing an automatic watering system (see below).
Step 1: Build an Olla
Seal the hole in what will become the bottom section of the clay pot. We bought a ceramic floor tile from Home Depot for 99 cents and broke it up into little pieces. Apply lots of waterproof silicon caulk around the opening and then stick a piece of the broken floor tile over the hole. We also caulked the other side (pot's exterior) of this hole with more silicon caulk just to ensure that leakage won't be a problem.
Next you'll need to attach the two clay pots together.
If you're using Gorilla Glue (as we do) you'll need to lightly wet one of the pots as shown in this picture.
We first use 100% waterproof Gorilla Glue. We let the Gorilla Glue dry overnight. We then put heavy amounts of silicon caulk over the connection (the Gorilla Glue leaves lots of tiny gaps). The end result is not very pretty, but it's watertight!
The finished product. We painted the top of the Ollas that will be exposed to sunlight with white paint. Since the top is now painted or glazed, evaporation will be greatly reduced. We learned this the hard way.
If you click on these pictures to enlarge them, you'll see where the potting mix is moist from the olla.
Ollas (Clay Pots) in Developing Nations
This is an excellent Phd thesis from a student at the University of Pretoria on the use of clay pots in developing nations. Lots of great information.
This research paper is from the OAS (Organization of American States). It also relates to clay pot's use in developing nations.
Automated Olla Irrigation
(Note: We're still testing this design. No guarantees of success.)
Newest Design : 6-29-10 : Still Testing.....
The goal of this design is simplicity, leak-free smaller ollas and gravity feed (no siphons).
a) 1/4" poly pipe
b) 1/4" "T"
c) 1/4" x 1 1/4" Fender Washer
d) Silicon Caulk
e) Plumbing Epoxy Putty (it's waterproof, easy to handle and safe for humans)
f) Terra Cotta Pot and Saucer
We used plumbing epoxy putty for everything, except when we used silicon caulk to attach and seal the saucer to the pot. We used two brands of plumbing epoxy putty. In the pictures, one brand is white and the other is gray.
That's white silicon caulk between the pot and saucer.
This week we'll attach a series of these ollas to a gravity fed 55-gallon barrel for the final testing.
1st Attempt at Automated Olla Irrigation
Result : Leaks!
There appears to be some water leaking where the 1/4" poly pipe enters the 7/32" holes. We're beginning to believe that the silicon caulk doesn't adhere 100% to the slick poly pipe. We are looking into alternatives.
We've modified most of our clay pots to implement our automatic clay pot water refilling system.
Step 1: Drill two holes in what will become the top section of the clay pot. Do this before you glue the two pots together. Use a 7/32" concrete drill bit. Later you'll be inserting 1/4" irrigation tubing into these two holes.
Step 2: You will also need to seal the the top drain hole that exists in the original pot. Do this before you glue the two pots together. Seal it like we sealed the bottom hole (ie silicon caulk and broken floor tile).
Because we modified our top pot after they were glued together (not recommended) they're really ugly!
A 4" clay pot is buried. One 1/4" tube is the water feed. The second 1/4" tube allows air to flow out when the pot is filling with water. Once the clay pot is filled with water, water travels through this second tube to the next clay pot in the series.
The 4" olla is completely buried.
This is a 6" olla. It takes up a large amount of space. We were unable to completely bury it.
This post will be updated throughout the summer of 2010 as we implement the olla system in Global Buckets.