Great to here that u r thinking of automation. I have also googled on the same few months before. Here are what I found.
Raspberry Pi as main controller. It can be controlled remotely and programmed to start and stop drip. Cost 3000 Rs.
Solenoid valve can be used with laterals to open and close valve supplying water. Cost approx 250 Rs.
Moisture sensor can be used to detect moisture level in sand. Cost approx 100 Rs.