TENSIOMETER-FOR JUDICIOUS USE OF WATER INPADDY Rajan Bhatt Assistant Professor (Soil Scinece) Krishi Vigyan Kendra,Kapurthala rajanbhatt79@rediffmail.com (98159-63858) Of all the planet’s renewable resources water has a unique place. It is essential for sustaining all forms of life, food production, economic development and for general well being. Although water is a renewable source its availability in appropriate quality and quantity is under severe stress due to increasing demand from various sectors. Water resources consists of both surface water and ground water resources. The main source of all the water resources is the precipitation in the form of snow and rainfall. The surface water available in the form of canal water is tapped by constructing dam and reservoirs across the river at suitable locations. The surface and ground water resources of the country plays a major role in agriculture, hydropower generation, livestock production, industrial activities, forestry, fisheries, navigation, recreational activities, etc. Agriculture sector is the largest user of water which consumes more than 80 per cent of the country’s exploitable water resources. The over all development of agricultural sector and the intended growth rate is largely dependent on judicious use of available water resources. Punjab is one of the
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Tensiometer-An Effective Technique to Save Water in Paddy
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TENSIOMETER-FOR JUDICIOUS USE OF WATER INPADDY
Rajan BhattAssistant Professor (Soil Scinece)Krishi Vigyan Kendra,Kapurthala
Reservoir and cork: It consists of two acrylic transparent tubes of specific dimensions.
The inner tube is fitted with the narrow mouth of a ceramic cup of diameter equivalent to
that of the outer tube. The upper end of the outer tube is fitted with a silicon cork. The
cork on the reservoir must provide an airtight seal for the tensiometer. The body tube
works as a reservoir, and the cork directly seals the system.
Ceramic cups: The ceramic cup is porous, but the openings are so small that when
saturated with water, air cannot pass through within the range of soil water tensions to be
measured. Water moving out through the porous cup causes the reading to change
indicating the suction, or tension, at which the water is being pulled by the surrounding
soil. Both the tubes and the ceramic cup are filled with distilled de aerated water. Before
filing the whole tensiometer with water the cup is saturated overnight with water.
Coloured Strips: The upper portion of the outer tube is marked with three colored strips
which coincide with the different levels of soil matric potential, based on the water level
inside the inner tube. The irrigation to rice crop is recommended when the water level
inside the inner tube just crosses the green strip and enters the yellow strip.
Working of Tensiometer
Principle
The water in the inner tube of the tensiometer equilibrates with the surrounding soil
through the ceramic cup and its level indicates the soil matric tension and hence the water
status of the soil. The colored strips guide the farmers for scheduling irrigation to rice
crop. When buried in the soil the ceramic cup of the tensiometer allows water to move
freely in or out of the tube. As the soil dries out, water is sucked out through the porous
ceramic cup, creating a partial vacuum inside the tensiometer which causes the water to
move down. Soil tension increases as the soil dries out, the vacuum increases in the
tensiometer and the water level falls down. When the soil is wetted by sufficient rainfall
or irrigation, water flows back into the tensiometer, the vacuum decreases and the water
level starts rising.
Tensiometers measure how tightly water is held to the soil particles and not how
much water is left in the soil. A sandy soil will reach a high tension sooner than a clay
loam because sandy soils cannot supply as much water to the plant and it is used up more
quickly. Tensiometers do not operate in dry soil because the pores in the ceramic tip drain
and air is sucked in through them breaking the vacuum seal between the soil and the
gauge on top of the tensiometer.
Installation of Tensiometer
Depth selection. The number of tensiometer installation sites required will
depend on the crops grown and field conditions. Fewer sites of tensiometers are needed
when a single crop is grown in large blocks of uniform soil. If the soils are varied or
different crops are to be grown, more sites are necessary. Sites need to be selected to
represent an area, and care should be taken not to cause excessive compaction or
destruction of plants around during installation, which may alter the condition.
Site selection. Location of the tensiometers in the field generally depends on the
type of irrigation system used. If the tensiometers are installed in a flood-irrigated field,
locations should be at the top and bottom of the first and last sets. Each location should
be far enough from the top or bottom of the field so that it is not affected by initial
wetting effects or by ponding of water. Placement should be in a crop row to avoid
traffic. Ceramic cups of the tensiometers must be kept wet until installed. A brightly
painted wooden stake or a metal rod with a colored flag attached are good markers.
Remove the silicon cork from tensiometer body and keep the tensiometer cup in a
container filled with distilled water and let it remain as such overnight till the
water level inside the tube is same as that of water outside in the container. Fill
the inner tube of tensiometer with distilled and de aerated water and keep it as
such over night.
Next day fill both inner and outer tubes of tensiometer with distilled water. Make
a hole in the field with steel iron tube of similar diameter to the depth of 20 cm.
The diameter of the hole should be slightly bigger than that of ceramic cup of
tensiometer.
Put the tensiometer into the hole and make slurry of soil and water in the ratio of
1:2 and put this into the hole around tensiometer cup. The remaining portion of
the hole can be filled with soil taken out of the hole.
Fit the silicon cork tightly. Tensiometer reading should be taken in morning hours
around 8..00 a.m. or so.
When the water level in the inner tube is within the green portion, there is no need
to irrigate the rice field and once it enters the yellow zone, rice field should be
irrigated. Don’t let the water level enter the red zone as it may cause stress to
crop.
When the field is re irrigated the water level in the inner tube will rise. If the
water level in tensiometer tube is less than 3 cm after irrigation, remove the cork
and refill the inner tube of tensiometer.
Irrigation timing with tensiometers
Tensiometers placed at about the mid-point of the main fibrous root system are used
to determine when to irrigate. This is particularly important during the period when the
water requirement of the crop is highest and yields are most sensitive to water shortage.
During this period tensiometers should be read daily. Sufficient amount of water should
be applied to re-wet the root zone. Following irrigation the reading on the tensiometer
will be reduced. Daily readings should continue to determine when irrigation is required
again.
When to irrigate will be determined largely by the amount of water applied and
stored in the root zone at the last irrigation. If only a light irrigation was applied, or a
small section of the root zone wetted, then the soil will dry faster and a high tensiometer
reading reached sooner than if a heavy irrigation was applied and all of the root zone
wetted. Climatic conditions and the leaf development of the crop will also affect the rate
of soil drying.
Conclusion
The use of soil auguring to feel the soil moisture and evaporation readings will
increase the accuracy of tensiometer irrigation scheduling. Pan evaporation readings are
particularly important as they are closely linked to the rate at which soil moisture will be
used. The combination of evaporation and tensiometer readings gives the irrigation
measurements of both climatic conditions and soil moisture, therefore enabling accurate
determination of irrigating timing and amounts.
Priority areas
In situ and ex situ conservation of rain water and its efficient recycling
Multiple use of water for increasing water productivity.
Conjunctive use of rain, surface and ground water for maintaining sustainable
hydrologic regime.
Increasing water use efficiency through efficient utilization of available irrigation
water in dry areas through promoting micro irrigating techniques.
Ground water recharge and management
Conjunctive use of poor and good quality waters.
Sources
Hira GS, Rachhpal Singh and SS Kukal (2002) Soil matric suction: a criterion for scheduling irrigation to rice. Indian Journal of Agricultural Sciences 72:236-37.
Hira GS, SK Jalota and VK Arora (2004) Efficient management of water resources for sustainable cropping in Punjab. Research Bulletin : Department of Soils, PAU, Ludhiana.
Prihar SS, PR Gajri and RS Narang (1974) Scheduling irrigation to wheat using pan evaporation. Indian Journal of Agricultural Sciences 44:567-71.
Sandhu BS, KL Khera, SS Prihar and Baldev Singh (1980) Irrigation needs and yield of rice on a sandy loam soil as affected by continuous and intermittent submergence. Indian Journal of Agricultural Sciences 50:492-96.