work by gravity
zero power self retaining irrigation method using gravity and spring action

Solution

There are mainly four sources  by which water is available

rain
nearby water body
public water supply by govt
well

either 1 or  2 or all are  available

well or storage tank is constructed to a considerable depth
well consist of a concave disc attached to spring
spring is such  that it gets compressed by weight of water above it+ weight of disc
disc has one way valve so t water goes only up and no back flow of water occurs
A another tank is present in middle of farm constructed to  a considerable depth 
water from big storage tank or well flow to it by means of gravity again by gravity water can reach the crops present in farm by means of pipe with valves for dripping action
 when the piston (i.e the disc plus spring) goes up vacuum is created which pulls water from nearby source .
if there is no source attach it to public water supply tap with a valve so that it can be opened when needed 
Water from main tank goes to tank kept high up in farm which also has a piston working similarly 
the farm tank has pipes attached with a dripping valves . Water comes down by gravity and through dripping valves reaches the crops. 
water overflowing is again attached to the main tank to avoid water loss
The cap above the tank are movable so that they can collect water