Water management in irrigated rice - Rice Knowledge Bank ...

0.5 cm in diameter and spaced 2 cm apart. Wrapthe perforated part of the tube in rough cloth suchas an old jute sack to prevent the holes from gettingclogged. Install this tube in a good and solid bundbetween the rice fields so that the tube protrudesabout 50 cm above the soil surface. An auger drillcan be used to drill the hole to place the tube in.Once the tube is installed, any groundwater willflow through the holes into the tube, so that thewater level inside the tube indicates the depth ofthe groundwater. Place a cap (can be made of anold tin) on top of the tube to prevent anything fromfalling in and blocking the tube.The water depth is measured from the top ofthe tube to the level of the water in the field usinga long stick or a piece of bamboo. Subtract 50 cmfrom the reading to obtain the depth of the groundwater(if the height of the tube above the bundis different from 50 cm, subtract the real heightinstead of 50 cm). A negative value means that thegroundwater has risen above the bund and that thearea is flooded. To make the measurement moreaccurate, the height of the tube protruding abovethe bund can be measured a few times during theseason to check whether it is 50 cm. To relate themeasured groundwater depth to the soil surface ofthe fields, subtract the height of the bunds from themeasurements. For example, with a bund height of20 cm, a groundwater depth of 100 cm below thebund equals a groundwater depth of 80 cm belowthe rice field.47