Automatic Irrigator Valve
There are many references in various electronic journals, design, or D-I-Y magazines to devices, which deliver water to plants based on monitoring the dryness of the surrounding soil.
All of them are electronic circuits, which require power for monitoring and power for the valve that delivers the water. The power has to be low voltage and available at the plant being watered.
The idea proposed now is to develop a non-electrical direct acting automatic irrigator, which can be attached to any drip irrigation system, or even any water pipe.
There are many polymers and polymer gels some of which are humidity sensitive. Choose one, which is not bio-degradable and changes volume with humidity. Make a low pressure valve with a rod made of this polymer attached to the valve seat. Bury this part of the valve at the place moisture has to be monitored.
On drying, the rod contracts letting out water. On hydration, the rod expands sealing off the water.
Reward: Greener Plants