Field instrumentation Crop and Environmental Sciences Division International Rice Research Institute Los Baños, Philippines
Field water balance lowland rice
Two types of instruments Instruments to measure water inflows and outflows Instruments to characterize field water status and groundwater ( hidden water source )
Two simple tools to characterize water environment and aid in field water management Field water tube Groundwater tube
Field water tube
With standing water on top of the surface: read this 20 cm diameter PVC pipe Use a ruler to Measure water depth 0 15 cm Soil surface Puddled topsoil 20 cm With water below the soil surface: read this Plow pan Holes are 5 mm in diameter, and spaced 2 cm apart
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
date Field water depths 150 100 50 0-50 -100-150 -200 Continuously flooded -250 Tuanlin 1999 150 100 50 Water depth [mm] 0-50 -100-150 -200-250 150 100 Tuanlin 2000 Controlled Irrigation 50 0-50 -100-150 -200-250 PhilRice 2001 date
Made of 5-cm diameter PVC pipe, 175-200 cm long, with perforations (0.5 cm diameter) in the bottom 50 cm. Groundwater tube 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
Cover (used tin can) 5 cm diameter PVC pipe Bund surface 50 cm Read here Groundwater level 100 cm 200 cm Measuring device Holes are 5 mm in diameter; 2 cm apart 50 cm
Groundwater measurements 20 0-20 -40-60 -80-100 Groundwater depth (cm) 18 38 58 78 98 118 Day number Tuanlin, China, 2002 20 Groundwater depth (cm) ( 20) 0 168 193 218 243 268 293-20 -40-60 -80-100 Groundwater depth (cm) Panicle initiation Flow ering Changle, China, 2002 Day number Harvest -20-60 -100-140 -180-220 -260-300 37270 37277 37284 37291 37298 37305 37312 37319 37326 37333 37340 37347 37354 37361 37368 37375 Dolores, Philipines, 2002
Soil water tension meter
Soil water tension in an aerobic soil 100 Soil moisture tension (kpa) 90 80 70 60 50 40 30 20 10 0 Panicle initiation Flowering Harvest 175 200 225 250 275 300 Day number
Instruments to measure water flows Rain + irrigation = evaporation + transpiration + percolation + seepage + overbund flow + d(storage) Specialized equipment: Inflows: rain gauge, flow meters Outflows: evaporation pan, percolation ring, seepage (?), surface water in channels Weather station to calculate evaporation and transpiration
Rainfall rain gauge The catchment funnel The measuring tube The fixing bracket The overflow tube Raingauge collector area 150 to 200 cm 2 30 cm to 1 m above the ground
Irrigation Flow meter in pressure pipes
Irrigation Box weir for surface water
Irrigation/drainage Simple weir for surface water
Irrigation/drainage Flume for surface water
Evaporation pan 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 rings Soil evaporation
Percolation 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
Percolation meter - measurement Put a mark on the wall of the cylinder. Always measure at this point Set water levels inside = outside. Reset water level if not. Take readings after reset Take readings d i and d f from water surface to the top of tube. Compute P = d i -d f After each reading, cover the cylinder to prevent other losses (rain, evaporation)
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) Temperature Humidity Evaporation pan Rain gauge Sunshine meter Radiometer Wind speed (missing)