The accurate determination of an irrigation schedule
is a time consuming and complicated process. The introduction of computer
programmes, however, has made it easier and it is possible to schedule the
irrigation water supply exactly according to the water needs of the crop
(rice). Ideally, at the beginning of the growing season, the amount of water
given per irrigation application also called the irrigation depths is small and
given frequently.
This is due to the low evapotranspiration of the young plants
and their shallow root depth. During the mid season, the irrigation depth
should be larger and given less frequently due to high evapotranspiration and
maximum root depth. This ideally the irrigation depth and the irrigation
interval (frequency) vary with crop
development.
When sprinkler and drip irrigation
methods are used, it may be possible and practical to vary both the irrigation
depth and frequency during the growing season. With these methods it is just a
matter of turning on the tap longer/shorter or less more frequently.
When a surface irrigation method is
used, how ever, it is not very practiced to vary the irrigation depth and
frequency too much. With in particular, surface irrigation variations in
irrigation depth are only possible within limits. It is also very confusing for
the farmers to change the schedule all the time.
THREE SIMPLE METHODS OF DETERMINING THE
IRRIGATION SCHEDULE IN RICE FARMING ARE BRIEFLY DESCRIBED
1. Plant observational method
2. Estimation method
3. Simple calculation methods
1. Plant
observation method: This is the method which is normally used by farmers in the
field to estimate when to irrigate. The method is based on observing changes in
the plants characteristics, such as changes in colour of the plant, curling of
the leaves and ultimately plant wilting.
II. Estimation
method – In this method, a table is provided with irrigation schedules for the
major field crop under various climatic conditions.
III. Simple
calculation method – This is based on the estimated depth (in mm) of the
irrigation application and the calculation irrigation water need for the crop
during the growing season.
SOIL AND WATER MANAGEMENT OF RICE
IRRIGATION-METHODS
Sprinkler
irrigates rice Land cradling-Establishing leaves water Delivery to fields – multiple
Inlet irrigation.
Sprinkler irrigated rice is very
limited at this writing. Research and experience show that the best potential
is either on clay or sandy lean soils 0that are relatively free of Johnson
grass. Many silt loan soils tend to crust which causes excessive runoff and
inadequate in filtration in the soil. This can lead to drought stress or
excessive irrigation which generally results in decreased yield and increased
pumping costs. Rutting and sticking of the center pivot is also a potential
problem. There is also a possibility that certain disease problems could be
increased when the foliage is whetted at the frequency associated with sprinkler
irrigation. Sprinkler irrigation should be used on experimented basis only.