USER MANUAL - Nieuwkoop BV
Contents
1. source Denarkas BV Path df the sal suction during the cultivation of CQrrysanthearum harvest groundwater rises 20 Soil suction hPa groundwater level around ground gats gets dry wet 5 4 12 4 19 4 26 4 3 5 Date 1995 20cm 35cm 50cm 60cm Groundwater level The numbers in the graphic give the irrigation in I m Connection and calibration of the TM I For electrical connection of the Tensiometer a 2 wire cable is required Remove and open the connector of the Tensiotube Connect to the Ub input connection 1 a power supply between 9 and 30Vdc The Ub out connection 2 is the 4 20mA output of the Tensiometer 4mA is equal to OhPa and 20mA is equal to 600hPa De enclosure of the transmitter is IP65 watertight When the Tensiometer is located outside or under an irrigation unit place the plastic protection cap over the Tensiotube This to protect the electronics IMPORTANT The Tensiometers are calibrated in the factory conform the specifications However the water column of the Tensiotube is not calculated in this calibration So at the zero point the tensiometer will indicate a value in hPa equal to the length of the tube in cm for example a tensiotube of 30cm will indicate at the O point 30hPa This can be compensated as follows Place the tube until half of the porcelain under water Wait until the readout has stabal2. the soil gets wet through rain or irrigation the Tensiometer will subtract water from the soil through the ceramic tip caused by the vacuum into the tube Because of this the vacuum will decrease until it is equal to the soil suction When the soil is saturated water can freely flow in and out the tube so there will be no vacuum into the tube In this way we can see the Tensiometer as a synthetic root of a plant where the vacuum is always in balance with the soil suction We can use this as a standard for the suction a plant needs to extract water from the soil Measuring vacuum The measuring principle of Tensiometers have been used in soil scientific research since 1930 These Tensiometers used Mercury or water columns to measure the vacuum Later this was replaced by a Bourdon pressure gauge Nowadays vacuum can be measured by electronic sensors With these sensors it is possible to measure the pressure more accurate The sensors have an electronic output that can be connected to a controller or computer The TM I of Nieuwkoop BV is a Tensiometer of this type The international standard for measuring pressure is Pascal Pa Other standards for measuring the pressure are hPa cm H20 column or pF However we will use the international standard and measure in hectopascal 1hPa 100Pa The conversion to the other units is 1hPa l1hPa 1 cm H20 column The pF is the logarithmic value of the pressure in hPa The pressure in the Tensiotube is measu
3. we will get a good view over the soil suction until 60cm deep into the soil 5 this makes it possible to create a wet zone of soil where roots can grow with under this zone a dry zone until the groundwater In this way drain will be minimised Tensiometer A is used to schedule irrigation With Tensiometer B the water flow from the wet to the dry zone will be measured Tensiometer C is to control if the dry zone stays dry enough This to avoid drain to the groundwater the Tensiometer value may not change after irrigation In this way we can fix the right time and duration of irrigation There has to be irrigated in this way the wet zone stays at field capacity then there will be enough water for the plants but no drain The irrigation time may not be to long It is very important to use an irrigation system which irrigates uniform and the irrigation water has to be very clean because of salt increasing We advise to connect the Tensiostations to a computer in order to make graphics of the soil suction over a few weeks or even a complete cultivation period This will give an overview of the soil suction over a longer period With this information we can schedule irrigation in a way the soil suction gets as equal as possible So it is not only important to control the actual value of the soil suction but also the variations over a longer period The graphic below is an example of the variations in soil suction in a chrysanthemum cultivation
4. USER MANUAL TM I 2 NIEUWKOOP V Tensiometer with electronic output USER MANUAL TENSIOMETERS Preface Congratulations with your Nieuwkoop Tensiometer The principal of Tensiometers have been used in soil scientific research since 1930 From that moment the Tensiometer is successfully used in agriculture and horticulture Nieuwkoop is manufacturer of Tensiometers in this sector for more than 25 years Using Tensiometers will give you a better opinion about soil conditions This makes it possible to tune irrigation schedules better to the needs of the plants This will result in a saving of water and nutrients and will give a bigger production The Tensiometer is a good help to minimalism the drain This will result in a better environment Thanks to the new line of Tensiometers with electronic output it is possible to have a continuous control of the soil conditions This will help you to protect the plants against diseases caused by to much water or less production because of water stress From now on guesswork in scheduling irrigation belongs to the past Good luck with your Tensiometer Summary Soil particles water and air are the main elements of every soil around the plant roots Water can not move freely in the soil but will be hold between the soil particles How easy water can move in soil depends on the soil type the capillary attraction and the amount of water These values determine how easy a plant can subtract w
5. ater from the soil see figure 1 and 2 Much water Little water meee MUU s 3 A rrr rrr T 3 PE ANY N 3 H jiy 7 4 YIAN 1 3 i fee b Mah AU big ana AAU fos E ETT a Soil Air Water Figure 1 Soil Air Water Figure 2 When the soil contains much water and even the big spaces between soil particles are filled with water the plant roots can subtract the water quite easy from the soil When the soil contains less water and only the small spaces between soil particles are filled the plant has to use more suction to subtract water from the soil When there is to much water in the soil soil particles can not hold all the water so water will drain away the soil is saturated When the water content decrease at a certain point the plant can not subtract water from the soil anymore this the withering point Measuring principal Tensiometers are the only instruments that measure directly the suction a plant needs to subtract water from the soil A Tensiometer consists of a hollow tube connected to a ceramic tip at the bottom A rubber stopper closes the tube at the upper side The tube has to be filled with demi water or distilled water After this the tube has to be placed into the soil When the soil gets dry it will subtract water from the tube through the ceramic tip This will cause a vacuum in the tube When the vacuum is equal to the suction of the soil the water flow through the ceramic tip will stop When
6. breakable so be careful with placing the tube Press the soil around the tube firmly and make the soil wet This will give the soil it s old structure back and irrigation water flowing along the tube will be avoided Because the soil is wet it will take some time before you can read out the Tensiometer 1 day 3 The Tensiometer has to be placed on a representative place Place the Tensiometer between the plants How deep the Tensiotube has to be inserted into the soil depends on which purpose the Tensiotube is used for When the Tensiotube is used for scheduling irrigation it has to be placed in the active root zone with the ceramic tip between the roots This is the place where plants extract water from the soil For deeply rooted plants we advise to use two Tensiometers one at 1 4 of the root zone and one at 34 of the root zone Because of this we get a better view of the soil suction over the complete depth of the root zone Place these two Tensiometers close together to avoid different readings because of difference in soil structure etc When the Tensiotube is used for controlling the drain place the tube with the ceramic tip under the active root zone right between the root zone and the groundwater until max 80cm deep Place the Tensiometer on a place that is representative for the whole parcel When some places on a parcel differs in moisture because of soil structure soil type or difference in height Place in both areas a Tensiomete
7. ised and calibrate on OhPa with the device where the Tensiometer is connected to We advise to return the Tensiometer once a year to Nieuwkoop BV or your own supplier for calibration Technical specifications Type Brand Range Max pressure Output Non linearity Hysterese Power supply Temp sensitivity 0 point Temp sensitivity Span Working temperature Accuracy 0 point Span Membrane Housing Connector Tensiotube lengths Tube Weight 30 60 and 90cm Accessories Warranty TM I Nieuwkoop BV Aalsmeer Holland 0 600hPa underpressure 2 times the range 4 20mA 4mA 0hPa 20mA 600hPa Typ 0 25 max 0 5 of the scale Typ 0 25 max 0 5 of the scale 9 30Vdc Typ 0 02 max 0 04 C of the scale 0 85 C Max 0 005 C of the scale 0 85 C 1 85 C 1 exclusive water column better accuracy possible by means of individual calibration Ceramic Stainless steel 1 4305 IP65 DIN 43650A 30 60 and 90 cm other lengths on request 20mm resp ca 300 360 and 420 gram Syringe 60cc and an user manual 1 year
8. ng of the Tensiometer with water The ceramic tip has to make good contact with the soil The Tensiometer have to be placed on a representative place The pores of the ceramic tip may not get choked up EOOD 1 Before placement the Tensiometer has to be filled with water Remove the rubber stopper from the Tensiometer Fill the tube with distilled or boiled water Avoid air bubbles in the tube Push the rubber stopper carefully back into the tube the tube may not have a leak Place the ceramic tip of the tube during a few hours into water When the Tensiometer is placed into the soil it will leak water very slowly How quick this will happen depends on the soil suction In practice the tube will start leaking water above 600hPa This will give an air column at the top of the tube This air gives a delay in reaction time Therefor we advise to refill the tube when the air column gets bigger than 1 cm This can be done by removing the rubber stopper refilling the tube with distilled water and pushing the stopper carefully back into the tube Because of this the Tensiometer will lose its vacuum so it will take a while before you can read out values again 2 For a representative measurement the ceramic tip has to make good contact with the surrounding soil In soft soil the tube can be pushed directly into the soil In hard soil firstly we have to drill a hole with the same diameter as the Tensiometer The ceramic tip of the Tensiometer is
9. oil suction is between 0 50hPa there is enough water for the plants This suction is normal after rainfall or irrigation In this measuring range water will drain quickly When the soil suction will be in this range for a long period more than two days this indicates poor drainage conditions This damage the plants 50 200hPa A soil suction of 50 200hPa means there is enough water and enough air for an optimum growth of plants Soil suction in this range is called field capacity of the soil This means soil can not held more water for the plants All the water what will be irrigated extra will drain after a while 200 400hPa The soil suction is good for plant growth in normal soil and soil with fine texture but in sandy soil the suction can increase quickly This will cause water stress 400 600hPa Soil suction is good for fine texture soils but in other soils the suction can increase quickly This will cause water stress 600 800hPa Available water for plants is scarce Even in heavy clay soil the suction can increase quickly This will cause water stress This is a coarse indication of the soil condition for plants In practice soil conditions are dependent on soil type and structure Beside this some plant types are more sensitive for water stress as others Because of this irrigation scheduling will differ for every user Placement and Maintenance For a representative measurement there are a few things important 1 Right filli
10. r to get a complete view in soil suction over the whole parcel for a good scheduling of irrigation Place Tensiometer always in the shadow This to avoid temperature deviation 4 The pores of the ceramic tip could choke up after a while To prevent this clean the ceramic tip every half year with a household cleaner N B The soil suction is measured through the water into the tube Because of this the Tensiometer will not work when it is freezing So do not use the Tensiometer below temperatures of 1 C Tensiostations To have a good view over the soil suction we advise to use more Tensiometers at different depths close together We call this a Tensiostation In figure 3 are three different Tensiotubes placed Tensiometer A is placed with the ceramic cup in the middle of the root zone of the plants here 20cm Tensiometer B is placed with the ceramic cup just under the root zone here 35cm The ceramic tip of Tensiometer C is placed in the middle between Tensiometer B and the groundwater level here 60cm The depths mentioned in the drawing are examples These will differ for everyone The depth of the root zone depends on plant type use for deeply rooted plants two Tensiometers as mentioned in point 3 at page 4 The depth of Tensiometer C depends on the groundwater level Do not placed Tensiometer C deeper as 80cm Wet zone root zone Dry zone buffer zone Fig 3 Groundwaterlevel 80cm In this way
11. red compared to the barometric pressure The Tensiometers will be calibrated in this way the pressure will be zero when the tube is placed in water When water will be extracted to the tube this will cause a vacuum so this will be a negative value for example 100hPa In graphic 1 you will find the suction in hPa of a certain soil compared to the moisture in percentage This graphic is different for every soil type 100 100 Soil Soil Pe Sandy soil a Clay soil Air Air vo Water v Water Available water Available water 0 0 500 hPa 1000 15000 500 hPa 1000 15000 Ls aturation point Wilting pointe Ls aturation point Wilting point p Graph 1 Graph 2 Measuring values Every soil type has a saturation point and a withering point At saturation the suction is OhPa and at the withering point the suction is about 15 000hPa Between these values a plant can extract water from the soil However in practice the soil suction will stay between 0 and 800hPa and irrigation will take place between these points The condition of the soil between these points is mainly as follows OhPa Soil suction of OhPa means the soil is completely saturated This can be expected after heavy rainfall or long irrigation When soil suction will be 0 for a longer period there will be oxygen starvation to plant roots and development of diseases A persistent zero reading after irrigation indicates poor drainage conditions 0 50hPa When the s
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