Field instrumentation

Crop and Environmental Sciences DivisionCrop and Environmental Sciences DivisionInternational Rice Research InstituteInternational Rice Research Institute

Los BaLos Bañños, Philippinesos, Philippines

Field water balance lowland riceField water balance lowland rice

Instruments to measure water inflows and outflows

Instruments to characterize field water status and groundwater (“hidden water source”)

Two types of instrumentsTwo types of instruments

Two simple tools to characterize water environment and aid in field

water management

• Field water tube

• Groundwater tube

Field water tube

Soil surface

Puddled topsoil

Holes are 5 mm in diameter, and spaced 2 cm apart

15 cm

20 cm

20 cm diameter PVC pipeWith standing water on top of the surface:read this

With water belowthe soil surface:read this

0

Plow pan

Use a ruler toMeasure water depth

Soil surface

Puddled topsoil

Holes are 5 mm in diameter, and spaced 2 cm apart

15 cm

20 cm

20 cm diameter PVC pipeWith standing water on top of the surface:read this

With water belowthe soil surface:read this

0

Plow pan

Use a ruler toMeasure water depth

Field water tube - installation

Push tube by

hand vertically

Drive cylinder

using mallet

Check clearance

from soil surface

Appearance of

installed PW tube

Remove soil

inside the tube

Check and level the

Top of the tube

Field water tube – measurement

Water depth = H – D

D = depth of field water table

H = height from soil surface to the top of the tube

A practical indicator for water in field

-250

-200

-150

-100

-50

0

50

100

150

-250

-200

-150

-100

-50

0

50

100

150

date

Wat

er d

epth

[m

m]

Tuanlin 1999

Tuanlin 2000

PhilRice 2001-250

-200

-150

-100

-50

0

50

100

150

date

ControlledIrrigation

Continuouslyflooded

Field water depths

Made of 5-cm diameter PVC pipe, 175-200 cm long, with perforations (0.5 cm diameter) in the bottom 50 cm.

Installed into a bund using an auger (soil dril) of the same diameter to the required depth

Should stick out about 50 cm above bund surface

Use stick to measure water depth

Groundwater tube

Bund surface

Holes are 5 mm in diameter; 2 cm apart

50 cm

100 cm

50 cm5 cm diameter PVC pipe

200 cm

Cover (used tin can)

Groundwater level

Read here

Measuring device

Bund surface

Holes are 5 mm in diameter; 2 cm apart

50 cm

100 cm

50 cm5 cm diameter PVC pipe

200 cm

Cover (used tin can)

Groundwater level

Read here

Measuring device

Groundwater measurementsGroundwater measurements

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-80

-60

-40

-20

0

20

18 38 58 78 98 118Day number

Groundwater depth (cm)

Tuanlin, China, 2002

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-80

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0

20

168 193 218 243 268 293

(cm)

Flow ering HarvestPanicle initiation

Groundwater depth (cm)Day number

Changle, China, 2002

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-260

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-180

-140

-100

-60

-20

20

3727

0

3727

7

3728

4

3729

1

3729

8

3730

5

3731

2

3731

9

3732

6

3733

3

3734

0

3734

7

3735

4

3736

1

3736

8

3737

5

Groundwater depth (cm)

Dolores, Philipines, 2002

Soil water tension meter

Soil water tension in an aerobic soil

0

10

20

30

40

50

60

70

80

90

100

175 200 225 250 275 300Day number

Soil moisture tension (kPa)

Panicle initiation Flowering Harvest

Specialized equipment:

• Inflows: rain gauge, flow meters

• Outflows: evaporation pan, percolation ring, seepage (?), surface water in channels

Weather station to calculate evaporation and transpiration

Instruments to measure water flowsInstruments to measure water flows

Rain + irrigation = evaporation + transpiration + percolation + seepage + overbund flow + d(storage)

Raingauge collector area

150 to 200 cm2

30 cm to 1 m above the ground

The catchment funnel

The measuring tube

The overflow tube

The fixing bracket

Rainfall rain gaugeRainfall rain gauge

IrrigationIrrigationFlow meter in Flow meter in pressure pipespressure pipes

IrrigationIrrigationBox weir for surface Box weir for surface waterwater

Irrigation/drainage Simple weir for surface water

Irrigation/drainageFlume for surface water

Keep away from other instruments (2x ht) Level the pan Install the stilling well and the fixed point Add water until the water reaches the tip of the fixed point and can

be seen as a small dot

Evaporation panEvaporation pan

Evaporation ringsEvaporation ringsSoil evaporationSoil evaporation

Percolation ringPercolation ring

20 cm in diameter cylinder - open on both ends

Covered – to avoid evaporation and rainfall

Percolation meter - installation

Push cylinder by

hand vertically

Drive cylinder

using mallet

Check clearance

from soil surface

Check and level percolation tube

Take readings di

and df from water

surface to the top of tube. Compute

P = di- df

Put a mark on the wall of the cylinder.

Always measure at this point

After each reading, cover the cylinder to prevent other losses (rain, evaporation)

Set water levels

inside = outside.

Reset water level if not. Take readings after reset

Percolation meter - measurement

Large percolation

ring in field

Rain + irrigation = evaporation + transpiration + percolation + seepage + overbund flow + d(storage)

As surface flow in drain

As “rest term” of balance

Weather station (o.a., calculate ET)

TemperatureHumidity Evaporation pan

Rain gauge Sunshine meterRadiometer

Wind speed (missing)