The amount of water that your plants need will depend on many factors in addition to the weather. For example, as the plants grow and become bigger they will need more water. Plants growing in sandy soil will need more water than plants growing in heavy soil.
To take account of all these additional factors, I recommend that you use a length of steel pipe to check the moisture level in the soil. I suggest that the diameter of the pipe be between 30 and 40 mm. An angle grinder can be used to cut a slot in the steel pipe so that you can inspect the soil inside the pipe. I suggest that the width of the slot be about 15 mm.
By checking the moisture level in the soil through the slots in the steel pipe, you can decide whether the plants have been irrigated with too much or too little water.
Early in the morning after irrigation at night, hammer the steel pipe into the soil near a dripper so that the slot faces the dripper.
Remove the steel pipe from the soil and use the slot to inspect the moisture level in the soil and the position of the wetting front. You may wish to use the slot to remove some soil from the pipe and to squeeze the soil sample between your fingers.
This video provides step by step instructions so that smallholders can use smart irrigation scheduling. All that is needed is a steel pipe and a storage container. Use for high or low pressure for any irrigation zone, big or small. The scheduling takes account of
the evapotranspiration of your plants
the soil type
the depth of the root zone
(uploaded 25 July 2019, duration 7:00)
An angle grinder can be used to cut a slot in a length of steel pipe
Hammer the steel pipe into the soil
Remove the steel pipe from the soil and use the slot to inspect the moisture level in the soil
An easy way to adjust your water usage rate is to use an adjustable dripper for your control dripper. Increase the flow rate to reduce the water usage, or reduce the flow rate to increase the water usage rate. For more details download the DIY Solar Measured Irrigation Training Manual for Smallholders or the Unpowered Measured Irrigation Training Manual for smallholders
A suitable adjustable dripper may be purchased online from the Measured Irrigation Shop.
After irrigation and adjustments over several days, the water usage should stabilise at an appropriate level for the plants at their current stage of growth.
As your crop grows and the water requirement of the crop changes, you may wish to repeat the process of adjusting the water usage rate.
An alternative way to adjust the water usage rate is to change the surface area of the evaporator by using a larger or smaller evaporator.
Increase the flow rate of the adjustable dripper to reduce water usage
Adjustable dripper used as control dripper