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NewsletterGei jkt N i e u w s
All it takes for environmental research
11Eijkelkamp Agrisearch EquipmentMarch 2003
Included in this number:• Interview DLV• De Water Cycle• The
‘Heath forest’ enigma• Soil moisture sensors• Grassmeter•
Divernews
Theme: Soil moisture
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2GEIJKT NIEUWS 11+31 313 88 02 00www.eijkelkamp.com
www.eijkelkamp.com
Arboriculturalists need to keep upwith the latest developments
in orderto be able to work with maximumefficiency and grow good
products.Arboriculturalists are alsoencountering ever more
complexlegislation and environmentalregulations. Remaining well
informedand making the right decisions at theright time involves
greatresponsibility. DLV Adviesgroep canprovide assistance in this
area. Theconsultants of the Tree Nurserymarket group are able to
providearboriculturalists expert, objectiveadvice tailored to
individual needs.DLV Boomteelt can assist and guidegrowers of
ornamental shrubs,conifers, roadside trees, roses, plants,forest
and hedge shrubs forpermanent and public gardens.
BABThe Tree Nursery IrrigationConsultancy System (BAB) is
thefavoured system for providing treenursery trees and shrubs with
theperfect amount of water at theperfect time. A simple method
allowsthe grower to test the moisture inthe soil by himself. Based
on the typeof soil he determines the amount ofwater that needs to
be given.
How doe the BAB actually work?The BAB system works in a
verysimple way. The measuring system isbased on determining the
soil watersuction power (suction tension). Thesoil water suction
power is the valuethat indicates how hard the plantneeds to suck
from the soil to beable to absorb water. This suctiontension is
measured with the use ofa read-out device (Watermark). Thismeter is
connected to four (or more)soil moisture sensors set into theground
(Watermarks). This makes itpossible to read the soil watersuction
power any time of the day ina simple manner.
Francois van Abeelen: “As part ofthe (financed) ‘Tree Nursery
WaterConservation’ project 10 companiesparticipated who represented
each ofthe ‘outdoor’ crop groups (roses,
roadside trees, conifers, forest andhedge plants). For a period
of threeyears the critical soil water suctionpower was measured
with the use ofthe Watermarks from Eijkelkamp.DLV selected the
Watermarks as itinvolved a project extending over anumber of years
and these deviceswere able to remain in the soilthroughout the
winter, since theWatermarks are particularly well-suited to
withstanding frost. The
In 1999 DLV Boomteelt, part of the DLV Adviesgroep
(DLVConsultants), commenced aproject that aims to promotemore
conservative use of wateramong growers. Next follows aninterview
with Francois vanAbeelen, Consultant for Nurserybusinesses with DLV
Boomteelt.Francois was closely involvedwith the BAB project
(TreeNursery Irrigation ConsultancySystem), during which
thepurchasing of a large number ofWatermarks became the
firstcontact with EijkelkampAgrisearch Equipment.
DLV AdviesgroepDLV Adviesgroep NV is a leading full-service
consultancy agency with amain focus on the agrarian
market,entrepreneurs in agribusiness, green
space and international markets. Thearboricultural section is
respondingto the ever stricter requirementsmade with regard to the
quality ofTree Nursery products.
DLV Tree Nursery Irrigation Consultancy
15 cm20 cm PrecipitionWatering
Soil moisture content, watering and precipitation of B2 Sandy
soil
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while at the same time thedifferences in yield from a field
canbe also be investigated.
Applications:• Yield estimates to establish the
best possible time for mowing or grazing
• Yield estimates for fertilising recommendations
• Grazing test for grassland research
• Precision farming for which it isnecessary to determine
thevariation in grass yield from afield (this often involves the
useof a geographic informationsystem)
• Information
3
11Grass heightmeter
A useful tool for estimating theamount of grass on a piece
ofland is the grass level meter.This meter is thereforeespecially
suitable for farmerswho wish to manage theirgrassland in the best
possibleway. At the same time themeter is a tool frequently usedin
research and for providinginformation.
Environment and cost factorsIt is important for good
grasslandmanagement that mowing iscarried out and that cattle is
shiftedat exactly the right time. When thegrass quantity is
excessive on aparticular piece of land,unnecessarily high losses
can occurif cattle are allowed to graze there.If too much length is
cut, thequality of the sward could beadversely affected while
regrowthwill often be poor. In additionfertilisation
recommendations areoften based on the degree of thenext cutting.
Grazing or mowingeither too early or too late canoften mean that
unnecessaryamounts of yield are lost or thatuptake of the
fertiliser that hasbeen applied is unnecessarily late.Keeping in
mind the environmentaland cost factors, knowledge of theexpected
dry feed yield is thereforeof considerable importance.
Fast and no mowing requiredThe NMI grass meter available
fromEijkelkamp Agrisearch Equipment isa simple, non-destructive
methodfor measuring grass height in aparticular field. It
allowsmeasurements to be taken speedilyand in relatively many
placeswithout the grass needing to bemown. In this way an
averagegrass height can be established
entire measuring system is durable,in fact. The project has by
now beencompleted but DLV is continuing thework by itself. It will
become moreand more worthwhile to participatein the application of
a waterconservation system such as this. Forgrowers in the province
of Brabant(NL), for instance, it means that ifthey apply this water
conservationsystem, they will receive a refund oftheir provincial
groundwater taxlevy!”
Taking measurements“The principle is as follows: For thegrowers
it is important that theymeasure the suction tension of thesoil
twice a week and that they faxthe data through to DLV Boomteeltin
Boxtel. In addition the growerneeds to pass on the
naturalprecipitation and the irrigationamounts. Once the data have
beenprocessed, it is therefore possible, atthe end of the growing
season, tocreate a clear overview of themeasured values. This in
turn allowsuseful conclusions to be drawnconcerning the irrigation
process.Matters such as ways to improve thewatering regime as well
as improvedgrowth are some of the benefitsexperienced by the
grower.
Additional growth spurtsIn Boskoop (NL) BAB helped toinvestigate
how 5 buxus (box)growers could ensure additionalgrowth spurts* in
the plants so thatthey would grow bigger. It was asuccessful
effort, and the growersconcerned are more than happy withthe
results”, Van Abeelen tells us.
*) Normally buxus (box) undergoes two growthspurts per year.
y System
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4GEIJKT NIEUWS 11+31 313 88 02 00www.eijkelkamp.com
New in the ‘Geijkt Nieuws’ newsletter:
The Water Cycle
Starting pointAs this cycle does not have a clearstarting or
finishing point, we willchose that part of the cycle that tiesin
most appropriately with thatparticular edition of Geijkt Nieuwsand
in doing so will fulfil our aim ofpresenting all relevant equipment
atspecific times.
Every stageIn its comprehensive product rangeEijkelkamp carries
measuring andsampling equipment that is suitablefor measurements
and sampling
throughout every stage of the watercycle. In this edition we
will featurethe part shown below that relates tomeasuring soil
moisture.
Soil moistureThe moisture content in the soil isone of the
determining factors foroptimal plant growth and cropproduction.
Moisture content in soilalso plays an important role
inenvironmental research intoacidification and pollution.Eijkelkamp
Agrisearch Equipment hasthe following equipment available:
• Soil moisture measuring system using gypsum blocks
• Watermark soil moisture measuring system
• Tensiometer (set)• Standard tensiometers• Jet-fill
tensiometers• Quick draw tensiometers• Electronic tensiometers
(Tensiors)• Thetaprobe• Profile probe• WET-sensor• Aquaflex• e+
SOIL MCT sensor• Trime FM-2 and FM-3• Trase / Mini Trase•
Rhizons
A new item in Geijkt Nieuws is the ‘water cycle’. Every three
months a new part of the water cycle will behighlighted and any
equipment associated with it that is available from Eijkelkamp
Agrisearch Equipmentwill also be featured.
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11
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PhD-projectTo end the controversy, theDepartment of
Geo-EnvironmentalSciences of the Vrije UniversiteitAmsterdam
initiated a PhD-projecttitled: “Hydrology andbiogeochemistry of
Heath Forests ofcontrasting stature in CentralKalimantan,
Indonesia” with financialsupport from the NetherlandsFoundation for
the Advancement ofTropical Research (WOTRO grantno.W76-217) in
October 2001. To test the drought stress hypothesisvarious types of
TDR equipment andrecording tensiometers wereinstalled. This along
withgroundwater tubes in four plotshaving different types of forest
alongthe gradient: Lowland Forest on Clay,Tall Heath Forest, Medium
HeathForest and Short Heath Forest (all onsand) in the Barito Ulu
area in theheart of Borneo.
TDR equipmentThe TDR equipment consists of theTRIME EZ, the
TRIME FM tube probeand TDR 3-wire probes, with the lasttwo being
read using a TRIME FM3device. Whereas the TRIME FM tube probegives
us daily readings at depthintervals of 5 cm, the TRIME EZprobes
provide us with a continuousseries of 30-minute soil
moisturecontent readings at single depths.The latter gives
information on howfast the soil is replenished after a
shower or how fast it dries out (on ahalf-hourly basis, although
one-minute measurements are possiblewith this instrument). Finally,
the TDR3-wire probe supplies information onthe spatial variability
of topsoilmoisture in the various plots.
TensiorNext to a considerable number ofmanually read
tensiometers toaccount for spatial variability in soilwater
tension, TENSIOR recordingtensiometers have been installed innests
of 3 tensiometers per plot,installed at different depths.
Soilmoisture tensions are recorded every15 minutes and stored on a
custom-made datalogger system on whichgroundwater levels are stored
aswell. Each tensiometer nest issupplemented with a TDR accesstube
for daily soil moisture contentreadings with a TRIME FM tubeprobe
at 5-cm intervals. Theadvantage of having both soil watertension
and moisture contentmeasured at the same depth is thatone obtains
field pF-curves fornatural wetting and drying cycles ofthe soil
which hopefully leads tomore realistic modelling of the soilwater
dynamics in the respectiveforests.
AnswerTogether with the continuousrecording of climatic
variables abovethe forest canopy, and of tree
sapflow rates using DynagageSapflow gauges, we hope that
thesesoil water measurements can beused in a
soil-vegetation-atmosphere-transfer scheme. This toanswer the
question whether andhow often the various types of HeathForests are
subject to water stress.The nutrient deficiency and soiltoxicity
hypotheses are beingaddressed through separateexperiments. For more
informationon the project please do not hesitateto contact the
field researcher and /or the project supervisor:
Field researcher:Ronald Vernimmen MSc (phone: +31 20 444 7334,
e-mail:[email protected]).
Project supervisor:Dr Sampurno Bruijnzeel (phone: +31 20 444
7294, e-mail:[email protected])
There is a long standing debate in tropical ecology as to what
are thecauses of the distinctive features of so-called Heath
Forest. HeathForests are a distinctive type of Lowland Evergreen
Tropical RainForest found exclusively on extremely acid white sand
soils. Theseintriguing forests have much smaller trees and
above-ground biomassthan ‘ordinary’ Rain Forest on clay soils,
while in addition HF leavesare small and leathery. All this gives
the impression that HeathForests may be subject to regular drought
stress, despite theabundant equatorial rainfall. Other theories
advanced to explain thepeculiar features of Heath Forests include
nutrient deficiencies andtoxic conditions in the soil.
The ‘Heath Forestenigma’
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creates an electrical field around themeasuring probes.
Depending on thecomposition of the soil the pulse isreflected with
greater or lesserspeed. Examples are: Trase, MiniTraseand Trime
(FM2 and FM3).
b) FDR: Frequency DomainReflectometers (Capacitancesensors) The
sensors consist of 2 electrodes(probes or metal rings).
Theseelectrodes generate a high electricalfield. The soil between
the twoelectrodes draws energy from this.This causes the fase of
the electricalfield to change. The greater thewater content of the
soil, the moreenergy is drawn off. Changes infrequency mean changes
in theelectronic characteristics of the soil
which is being measured. In thesame way as with TDR,
thoseelectronic characteristics also dependon the volumetric
percentage ofwater in the soil. Examples are:
Aquaflex, Thetaprobe, Profileprobe,WET sensor and the e+ SOIL
MCTsensor.
Measuring systems for soil watersuction tensionWater in the soil
is attracted, as onemight say, by the soil particles towhich it
adheres. When the soil iswet it means that many of the smallas well
as the large pores in the soilare full of water, meaning that
thewater is able to flow fairly easily.When the soil dries, the
water firstdisappears from the large pores andthen from the small
ones in which itis retained with more force – and it isthis force
that is also called suctiontension or power. Suction tension isan
important unit used in theagrarian as well as the green
sectors.
Examples of measuring systems thatmeasure suction tension are:
theTensiometer / set, standardtensiometers, Jet-Fill
tensiometers,Quick draw tensiometers, Electronic
Measuring systems that show soilmoisture content as a
volumetricpercentageThe soil is made up of three differentelements:
soil particles, water and air.The measuring instruments from
thisgroup take measurements in aparticular soil volume and
determinewhat percentage of that volumeconsists of water. The
volumetricpercentage of water can beconverted with the use of a pF
curveinto soil water suction tension. Thewater volumetric
percentage is avalue that is of particular importancefor
hydrological and agro-scientificresearch.
a) TDR: Time DomainReflectometersThe measuring principle
involves the
use of metal measuring probes thatact as transmitters of a TDR
signal. Ahigh frequency pulse is sent alongmeasuring probes and a
cable that iscalibrated to an exact length and this
6GEIJKT NIEUWS 11+31 313 88 02 00www.eijkelkamp.com
The soil moisture sensor range An important part of the
Eijkelkamp product range is made up of different soil moisture
sensors. Inaddition to the e-SENSE with its unique e+ sensors, a
system developed entirely by Eijkelkamp itself,Eijkelkamp can also
offer a number of alternatives. The measuring systems are divided
into 2 groupsbecause soil moisture can be expressed in 2 important
units: in volumetric percentage (water content inthe soil expressed
in % terms) and in soil suction tension (the energy required to
extract available waterfrom the soil). A description follows below
of the types of measuring systems Eijkelkamp can offer:
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e+ SOIL MCT sensorEijkelkamp Agrisearch Equipment hasdeveloped a
new Soil Moisture,Conductivity and Temperature sensor inits e+
sensor product range. Measureddata are stored internally and can
betransferred to the user via the e-SENSEtelemetry system or
directly to ahandheld readout or PC.
Measuring principlesPermittitivity and conductivity are
electricalproperties of materials. The permittivity is a
measure for to what extend the material canbe polarized. Because
water is a bipolarmolecule it has a high permittivity value,while
dry solid materials and air have a lowpermittivity value.
Therefore, the permittivityvalue of wet materials is dominated by
itswater content. The measuring principle ofthe sensor is based on
the Frequency DomainMethod (FD), described by van Balendonckand
Hillhorst (IMAG), at a excitationfrequency of 30 MHz, from which
the systemderives:• Permittivity• Conductivity• Temperature
11tensiometer and the Mini Tensior.
a) TensiometerA tensiometer is a transparent plastictube which
has a porous ceramic cupfitted at the lower end. This tube isfilled
with demineralised or boiledwater. Next it is placed in the
soilwith a special auger or drill. As soonas the soil dies out, a
small amountof water is drawn off through theceramic cup and the
tube. Thissuction tension or power can be readwith the use of a
manometer that isattached to the top of the plastictube.
b) Gypsum blocks / WatermarksGypsum blocks and Watermarksemploy
the simple principle ofelectronic resistance. Two electrodesare
used to measure the resistance inthe gypsum blocks. When the
soilcontaining the gypsum blockbecomes wet, the pores in thegypsum
fill up with water causingpart of the gypsum to be dissolved.The
water then conducts theelectricity independently from the
salt content in the water. The wetterthe block becomes (and
thereforealso the soil) the lower the electricalresistance in the
block. When the soilaround the block dries out the wateris drawn
from the block. The waterdisappears from the large pores firstand
then from the smaller ones. Theelectric current between the
2electrodes now needs to travel alonger distance through
smallerpores, causing the resistance to beincreased. This
resistance can beconverted into suction tension. TheWatermark works
on the sameprinciple as the gypsum blocks. Inthe case of the
Watermark thegypsum block covered by granulatefilling and cased in
a synthetic coverwith perforations which extends itslife. In
addition it is also moreaccurate because a temperaturecorrection
can also be performed.Both measuring systems (Gypsumblocks as well
as the Watermarks)come with a handheld meter.
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C O L O F O N© 2003 - Geijkt Nieuws is published byEijkelkamp
Agrisearch Equipment.Nijverheidsstraat 30, 6987 EM GiesbeekT +31
313 88 02 00F +31 313 63 21 67E [email protected]
Editorial address:Eijkelkamp Agrisearch Equipment.PO box 4, 6987
ZG Giesbeek,the Netherlands
Editors:Laura van der Lecq
Printing: Drukkerij Hooiberg, Epe
News
GEIJKT NIEUWS 11+31 313 88 02 00www.eijkelkamp.com
Software
The universal software programLogger Data Manager (LDM) hasbeen
developed to increase the easeof use of the Diver. LDM enables
youto program and read out themeasurements from dataloggers, andto
view the measurements. Theprogram creates a database,therefore it
is no longer necessary tostore each set of measurements readout
from the dataloggers in separatefiles. When you read out
themeasurements from a datalogger,the data is automatically
storedunder a unique combination oflocation code, logger serial
number,date and time. This precludes theaccidental overwriting of
oldmeasurements with new measure-ments. Logger Data Manager
offersmore opportunities to save thedefault settings.
Programming LDM can be installedon a desktop orportable PC and
worksunder Windows 95,2000 and Windows NT(4.0). The
standardread-out unit isattached to the PC.The read-out
unitprovides the linkbetween the Diver and LDM. UsingLDM makes
programming the Divereasy. Once programmed, the Divercan be
deployed in the field.
Reading out The internal memory can be read outas soon as
required. This involvesattaching the Diver to a (portable) PC
by means of the read-out unit. Thedata, the groundwater levels
and thetimes at which they were recorded, isdownloaded directly
into thecomputer. The data can be displayedin either graphical or
chart form. It isalso possible to convert the dataformat directly
so it can be processedin a spreadsheet program.
Dataprocessing The Logger Data Manager softwareis equipped with
a barometriccompensation wizard speciallydeveloped for the Diver.
This toolmakes it possible to correctgroundwatermeasure-ments
stepby step tocompensatefor changesin the
atmospheric pressure during themeasurements period. It also
makesit possible to relate the measure-ments to a specific
reference point,such as the top level of the borehole.
Logger Data Manager11
Wasser Berlin, Germany7 to 11 April
Demo day Germany10 April
Demo day University Ghent,Belgium19 and 20 April
Demo Sonic Belgium15 to 16 April
Meteo Hydex Geneva,Switzerland6 to 8 May
Consoil Ghent, Belgium12 to16 May
Distributor seminar Giesbeek,Holland20 to 23 May
Water ManagementExhibition Kielce, Poland16 to 17 June
The management of groundwater resources is of vital
importanceworldwide for nature, agriculture and for the supply of
drinkingwater. The need to measure and record groundwater levels
isbecoming increasingly apparent to all parties involved. The
Divergroundwater dataloggers are at the cutting edge in the market
forthis application. Eijkelkamp has been selling Diver® by Van
EssenInstruments for over five years worldwide.
C a l e n d e r