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
-100
-80
-60
-40
-20
0
20
18 38 58 78 98 118Day number
Groundwater depth (cm)
Tuanlin, China, 2002
-100
-80
-60
-40
-20
0
20
168 193 218 243 268 293
(cm)
Flow ering HarvestPanicle initiation
Groundwater depth (cm)Day number
Changle, China, 2002
-300
-260
-220
-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)