Page 39 - soil-plant-water relationship and water requirement
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SOIL-PLANT-WATER RELATIONSHIP AND WATER REQUIREMENT





















                                              Figure 3.4.4-1: Neutron Probe

                       3.4.5   Gypsum Block

                              This consists of a porous body with two electrodes embedded into it.  The
                              porous body when buried equilibrates with the soil water and the readings are
                              obtained through the resistance meters attached to the electrodes.

                              Resistance  units  are  measured  and  the  instrument  needs  to  be  calibrated
                              against matric suction or volumetric moisture content (Pv).  Various porous
                              bodies needed are gypsum, nylon or fibreglass.

                              The instrument is relatively cheap but it takes a long time to equilibrate or
                              react  e.g.  48  hours.  The  method  is  insensitive  in  wet  soils  <0.5  bars.  It
                              measures from 0.5 to 15 bars and more.
























                                                 Figure 3.4.5-1: Gypsum Block











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