In Greenhouses The international magazine for greenhouse growers Number 4 October 2015 Volume 4 Focused fertilisation requires knowledge, insight and experience Page 34 Production very closely linked to amount of intercepted light Page 23 High quality tomatoes in innovative plastic greenhouse in Mexico Page 7 Automatic container filler prevents errors during fertilisation
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In Greenhouses€¦ · Jojanneke Rodenburg Harry Stijger Pieternel van Velden Editor Helen Armstrong Design Van de Sande, Nootdorp Theo van Vliet Contact Advertising sales Holland
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In GreenhousesThe international magazine for greenhouse growers
Number 4
October 2015
Volume 4
Focused fertilisation requiresknowledge, insight and experience
Page 34 Production very closelylinked to amount of intercepted light
Page 23 High quality tomatoesin innovative plasticgreenhouse in Mexico
Page 7 Automatic containerfiller prevents errors during fertilisation
1-IG-Cover-no4-okt-eng-2015.indd 1 28-09-15 08:55
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“Even in the summer it can
take hours before the correct
EC reaches the last point.”
Page 44
3
Feature
Research
Report
5 Introduction chief editor Henk van Esch
15 Local report: Burston Nurseries (UK) breaks with
tradition and grows roses from cuttings
23 Local report: Hydroponic Green Valley Produce: Innovative
plastic greenhouse for high quality tomatoes in Mexico
33 The series of pests and diseases: Phytophthora
48 Local report: Dutch entrepreneur teaches local producers in
Georgia how to produce more effectively
51 Product news
Columns
9 Phalaenopsis distributor Eric Moor
17 Tomato grower Frank van Kleef
12 DNA is the recipe book for all the processes in the plant
30 When choosing a glass type also consider the cleaning of it
34 Production very closely linked to amount of intercepted light
42 ‘Avoid delay when distributing fertilisers and crop protection agents’
46 What the slab says is not
automatically the opinion of the plant
10 Alternative to iron chelates tests positive in practise
18 Market ready for affordable roof with high level of insulation and light transmission
26 Extra light and save energy in ideal winter-light greenhouse
39 News from Wageningen UR Greenhouse Horticulture
40 Short term non-chemical approach to Tuta absoluta and thrips
7 Automatic container filler prevents errors during fertilisation
20 Innovative fertilisation concept for chrysanthemums also looks at soil condition
28 Ethylene gives better control over the ripening of tomatoes
36 No lighting, but still two energy screens without dehumidification
44 Creative device is extra tool in fight against adult thrips
Coverphoto
Dutch strawberry nursery, Van Gennip Kwekerijen, chose a fully automatic fertiliser container filler. (page 7) Against higher costs there are big benefits: convenience, prevention of errors and saving on expensive management time. (Photo: Wilma Slegers)
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5IN GREENHOUSES NO 4 OCTOBER 2015
Colophon
Contributors
Contributors to this issue Marleen Arkesteijn Helen ArmstrongJos BezemerAnita ElingsEp HeuvelinkKarin van HoogstratenTijs Kierkels Frank van KleefEric MoorJojanneke RodenburgHarry StijgerPieternel van Velden
EditorHelen Armstrong
Design Van de Sande, NootdorpTheo van Vliet
Contact
Advertising sales Holland and BelgiumWouter van EschTelephone: +31 6 - 16 47 69 98E-mail: [email protected]
International advertising sales Horti Media SalesMiguel Mendes de LeónTelephone: +31 6 - 81 54 33 66E-mail: [email protected]
Editorial In Greenhouses is published byHorti-Text BV Bastion Willem 183445 DH WoerdenThe Netherlands
Digital archiveAll editions are digitally available on our site.
Subscriptions and change of addressTo request or terminate a subscription or inform us of a change of address simply go to www.ingreenhouses.com and click on the heading Readers.
Or by post: In GreenhousesPostbus 262630 AA NootdorpThe Netherlands.
Introduction
Fertilisation is a tricky subject, whether the crop is in soil or in a substrate. It’s because many
factors play a role in fertilisation. Compare it, for example, with temperature. For this you only
need a thermometer, linked or not to a climate computer, that precisely displays the situation.
With fertilisation it’s not only the various elements that play a role, but also the relationship
between the elements, the concentration of the elements and thus the amount of water that
a grower supplies. It becomes even more difficult when you include the uptake by the crop
as well.
Many growers base the fertilisation on a crop recipe. But Dutch research shows that
this is not always accurate: the plants don’t always get what they need. This is because the
measurements taken in the slab may not show the actual requirement of the plants. This
has led to the design of a new method (page 46). By using a model, a nursery can determine
the actual uptake by the plant. In this way a grower can provide
fertilisers in a much more focused way.
Nearly all modern greenhouse nurseries utilise a fertilisation unit
which, as standard, uses an A and B container with an automatic pH
control. The preparation and filling of the containers is an exact job;
mistakes are mercilessly punished through loss of yield and quality.
For this reason more growers are switching to automatic container
fillers (page 7). This requires an investment but they do save money
too and more importantly they prevent mistakes.
Good fertilisation requires knowledge about the chemical elements but you also need
to know the effect of each individual element. The role of the most important nutrients
is covered in the book, Plant Physiology In Greenhouses, which can be ordered via our
website www.ingreenhouses.com/books. With this information a grower can further develop
his knowledge and understanding and thereby further optimise production in terms of both
quantity and quality.
PS. Next issue of In Greenhouses will be published January 2016 just before IPM Essen.
Focused fertilisation requires knowledge, insight and experience
HENK VAN ESCHCHIEF EDITOR
“Good fertilisation requires
insight into the chemical elements
and their individual effect.”
The contents of In Greenhouses has been compiled as carefully as possible and to the best of the publisher’s and authors’ knowledge. However, the publisher and authors cannot in any way guarantee the accuracy or completeness of the information and they accept no liability for damage, of any nature whatsoever, resulting from acts and/or decisions based on the information included in this journal. No part of this publication may be reproduced, stored or made public without prior written consent from the publisher and authors.
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IN GREENHOUSES NO 4 OCTOBER 2015 7
Strawberry grower Theo van Gennip: “One error during fertilisation can be very costly.”
Nurseries that are starting to invest again are choosing remarkably often for fully automatic fertiliser container fillers. Dutch strawberry nursery Van Gennip Kwekerijen already has four and a fifth is in the pipeline. Theo van Gennip is very pleased with his choice: “It is always accurate, you don’t have to drag heavy bags and you save on expen-sive man-hours.”
Even a large horticultural company usually
has a very flat organisational structure: One
director, one manager, several people with
a certain specialism and many unskilled
labourers. That means that work that requires
great accuracy, automatically ends up being
done by the owner or manager. And their
time is expensive.
“In the past it used to cost me one and
half hours every three days just filling the
fertiliser containers. I used to use a litre
counter, which you had to rinse and reset
every time you switched to a different
fertiliser ingredient. You really have to pay
attention because one mistake can cost a lot
of money. And at such a moment the tele-
phone goes, of course. Then you’re no longer
certain where you were! Since we started
using automatic liquid fertiliser container
fillers we have had far fewer worries,” says
Theo van Gennip.
Many advantages Together with his three brothers and another
grower, Theo owns Mts. Van Gennip Kweke-
rijen that has five locations in the southeast
of the Netherlands. They grow strawberries
under glass, in gutters and in soil and they
Text: Tijs KierkelsImages: Wilma Slegers
STRAWBERRIESREPORT
No more topping up nutrient containers in the weekend
Automatic container filler prevents errors during fertilisation
Iron is an essential element that is requi-red for the formation of chlorophyll and in doing so prevents chlorosis. Because the element doesn’t usually remain dis-solved in a solution – and therefore is not available to the plant – for years growers have been using iron chelates. With the launch of a new fertiliser the iron is bound in a different way, namely in combination with polyphosphates. When given via a separate container it appears to work well in practice. The fertiliser also produces other effects such as less leaf curling and it makes UV dis-infection of drain water more efficient. Recent research and practical experiences support these findings.
In 2012 and 2013 Wageningen UR Greenhouse
Horticulture, in the Netherlands, was commis-
sioned to carry out research on the fertiliser
Micronutri Fe by the producer, Prayon. Kurt
Verhelst explains the reason for the research.
“The horticultural sector had been using
organic chelates for decades to ensure that
the plant could take up iron. As a large
phosphate supplier we think that a mineral
fertiliser based on iron polyphosphate has the
same effect. In addition, it prevents problems
during UV disinfection. Of course there is
scepticism, so with proper research we want
to validate its activity.”
During the trials the new fertiliser was
compared with the iron chelate DTPA. Both
products were found to prevent chlorosis
equally well. In addition, the new fertiliser
appeared to have a favourable effect on
calcium transport in the plant, so less leaf
cupping occurred. The fertiliser was launched
on the market at the end of 2013.
Calcium uptakeDutch high wire cucumber grower, Jan Reijm,
of Berkel en Rodenrijs, was one of its first
users. Ewoud van der Ven, crop advisor at
DLV Plant, gave him advice. “Last year I grew
a cucumber variety that was sensitive to leaf
necrosis at the top. That’s why I especially
chose this fertiliser because– in addition to
the prevention of chlorosis – it also seems to
improve calcium uptake,” says Reijm.
Although the crop developed well, he still
questioned its application. “We take weekly
samples of the drain water and we saw the
iron level drop each time. Although the plants
remained lovely and green, we were worried
about that decline. Time and again I gave
more iron polyphosphate. That’s why in the
autumn I switched over to ferric oxide just to
be sure.”
Research carried out againAfter this experience in the nursery, the manu-
facturer decided to ask Wageningen UR Green-
house Horticulture to carry out research
again on this fertiliser and a few other new
ones. Wim Voogt led the research. From Sep-
tember to November 2014 a trial was carried
out on a substrate-based crop of cucumbers
and from January to April 2015 on a tomato
crop to compare the new fertiliser with DTPA
iron chelate. Both trials had the same objec-
tive. Voogt: “The first question for the resear-
chers was whether the iron content remained
stable. And the second question was whether
indeed the fertiliser led to less leaf cupping in
cucumber and less tipburn in tomato, which
could suggest a better calcium transport.”
Dry matter analysisIn order to answer the first question the
water supply and the drain water were inten-
sively sampled in both trials. The results
confirmed what had been seen in practice:
The iron concentration in the drain water
was significantly lower than in the drain
from the plants that had received the iron
chelates. Especially when the pH rose above
6.5, the iron was released much more easily
and disappeared from the solution.
But that does not say everything about the
Text: Karin van HoogstratenImages: Studio G.J. Vlekke
NUTRITIONAL ELEMENTS RESEARCH
Separate administration gives better results
Alternative to iron chelates tests positive in practise
Verhelst: “With proper research we can validate the activity of the fertiliser.”
Van der Ven: “By dosing separately the fertiliser is not crowded out.”
Wim Voogt: “Iron polyphosphate leads to less leaf cupping in cucumber.”
It’s sometimes called a blueprint: DNA, the carrier of genetic information. But the term recipe book covers it better. It explains how the plant can respond to changing conditions. Plant breeders take advantage of natural variations in DNA. Genetic modification can make their job easier.
DNA is short for deoxyribonucleic acid.
A bizarre name for what can be called the
mystery of life. Only a variation in the
bases in DNA determines the vast diversity
of all living things. There are just four of
these bases: guanine (G), cytosine (C), adenine
(A) and thymine (T). A gene is then charac-
terised by a long series of letters consisting
merely of these four options, for example,
AAGCTTACC and so on.
Long spiral staircase DNA is often presented as a very long spiral
staircase. The banister and railing is made
from a sugar and a phosphate group. The
treads are made up of bases. A base is a mole-
cule with a free electron pair that can be
shared with an acidic molecule. These bases
are always connected in the same way to
each other. A is always opposite T and C is
always opposite G.
In order for an inherited trait to be
expressed, the gene has to be readable. The
bases then let go of each other, allowing the
strands to become free. Then messenger RNA
is formed which copies precisely the codes
on the gene. This message is sent to the
ribosomes where it is read and the protein
is made.
Researchers often say that a gene encodes,
for example, resistance to fungi. But strictly
speaking genes encode only for the produc-
tion of proteins, the plant’s building blocks.
The order of bases in the gene determines
the order in which amino acids bind to each
other and form proteins. This is a remarkably
simple code. The combination of just three
bases, for example AAC, determines which of
the 20 amino acids is next in line. The order
of the amino acids in the protein determines
the way in which the protein is folded. And
the way of folding is crucial to its behaviour.
A small mistake in the transcription can
make it completely ineffective.
The same genetic information All cells have the same genetic information.
For example, the cells in a tomato leaf also
contain all the information needed for flower
and fruit formation. This is easy to appreciate
knowing that complete plants can be produ-
ced from tissue taken from a piece of leaf.
How then do leaf cells remain so orderly
and not suddenly start to make flowers or
fruits? This is because most genes are ‘swit-
ched off ‘. The DNA is folded up and packed
inside the nucleus. If a gene has to be read it
first has to be made accessible. Regulatory
proteins take care of this. They, as it were,
switch ‘on’ the gene. The stimulus to do
this comes from, for example, external
circumstances (such as climate) and plant
hormones.
It’s remarkable that the majority of DNA
doesn’t code for anything. It’s called junk-
DNA. This accounts for 97% of the total DNA
in humans.
Text: Ep Heuvelink (Wageningen University) and Tijs KierkelsImages: Wilma Slegers and Marleen Arkesteijn
All cells have the same genetic information
DNA: The recipe book for all the processes in the plant
During crossing genetic material comes from two sources creating a new set of double genes. The
breeder is not able to control whether a desired characteristic in the mother is passed on to the
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configuration.
The UK would seem synonymous with garden roses. However, in recent years new housing developments have produ-ced much smaller gardens, traditional front gardens have been replaced with parking areas for cars. Therefore roses, like other hardy nursery stock has suffered and seen sales decline. Burston Nurseries, a major supplier of bedding plants and roses to the British garden centre industry, is bucking the trend by introducing ranges of modern roses, using innovative breeders and selecting only the very best.
Burston Nurseries has been at the heart of the
UK garden plant industry since it started tra-
ding in the 1963. Its late founder, John Pearson,
was a pioneering figure in the industry from
the 1950s onwards and one of the first chair-
men of the British Bedding Plant Association.
Also, its central location close to St Albans,
gives it easy access to major motorways for fast
distribution throughout the country. Today the
nursery covers around 10 ha including around 3
ha of glasshouses and poly tunnels, plus
offices, warehousing and cold storage facilities.
The nursery originally grew roses and later
on introduced bedding plants. Now around
70% of production is bedding plants and
30% is roses. It still produces well over 300
varieties of roses and a similar number of
bedding plants, mostly pansies, primulas and
polyanthus in the autumn and a full range of
summer plants from Non-Stop begonias to
geraniums and calibrachoa to surfinia for
the hanging basket market. These are sold
to shops, independent garden centres and
garden centre chains. “We also have a garden
centre onsite and this enables us to trial any
new products or varieties prior to going to
market in larger quantities,” says nursery
manager, James Alcaraz.
Text: Helen ArmstrongImages: Burston Nurseries
ROSESREPORT
Pioneer in bedding plants still at the forefront
Burston Nurseries grows roses from cuttings and breaks with tradition
Exactly one year ago Wageningen UR Greenhouse Horticulture and a consor-tium of Dutch companies started buil-ding a new, energy-efficient greenhouse. The key component is a cavity roof, with ventilation, made of clear glass under which is a layer of durable diffuse film. This autumn those involved will weigh up its assets but it already looks like that this innovation will benefit Next Generation Growing. The system looks professional and visitors have reacted positively.
A group of growers are just ending their tour
through the tomato crop as researcher, Frank
Kempkes, and general manager, Arno van
Deursen of Van der Valk Systems, enter the
trial greenhouse for a photo. The growers
visit the 2SaveEnergy greenhouse in Bleiswijk
(Netherlands) weekly and advise on the next
cultivation strategy. “Of course they also
monitor the progress,” explains Kempkes.
“And up to now no technical problems have
occurred in the crop.”
Energy savingThis time too the group was satisfied. It was
11 May and the first day of summer weather
this year. The plants were in good condition;
a strong top, eight clusters of six fruits had
been harvested and a ninth cluster was in
flower. Only the setting of the fifth cluster
had been a little slow but it looked like the
crop (cluster tomato Capricia RZ) would
make it to November.
The aim of the trial is to use a maximum
of 19 m3 gas for the entire cultivation period
to harvest 63 kilo tomatoes per m2. This is
7 m3 less than the 26 m3 that was achieved in
a trial with a ‘standard greenhouse’ for the
Next Generation Growing. That had two
moveable screens, a fixed film in the start-up
phase and a dehumidification system that
used air sucked in from outside. If they meet
their target those involved hope to prove that
the energy efficient properties of the insula-
ted greenhouse roof will be an extra gain for
sustainable production. And they are well on
track: by mid May they had used just 8.8 m3
of gas.
Insulated cavityKempkes and Van Deursen are pleased that
the greenhouse actually does what they had
worked out on paper. Van Deursen: “Fortuna-
tely it works, because you devise such an
innovation for eventual use in practise. That’s
why we continuously take into account the
availability and suitability of the materials
and techniques that we are use during the
development phase.”
The concept works. The innovative green-
house is based on Next Generation Growing
and builds on the ID Greenhouse by Techno-
kas and Duijvestein Tomatoes, in the Dutch
Text: Jojanneke RodenburgImages: Studio G.J. Vlekke
DOUBLE ROOF RESEARCH
Next Generation Growing even more energy efficient
Affordable roof with high level of insulation and light transmission
Contrary to the plans made on paper, the trial greenhouse is equipped with a double glazed roof comprising clear glass and a diffuse foil. This
choice, motivated to provide assurance, is also financially beneficial.
Huisman Chrysanthemum in the southwest of the Netherlands produces 13 million Bonita stems annually. After switching to the new fertiliser
concept quality has remained high.
Chrysanthemum grower Peter Huisman has over the last year applied the Hori-zon fertilisation concept to his nursery in Maasdijk, the Netherlands. On one hand this strategy takes into account the emissions and the needs of the crop and on the other hand the structure of the ground. The biggest change for the grower is the method of administrating the fertiliser. “Previously we gave the necessary nutrients in the irrigation water, now we scatter over granules before we start cultivating. This stock of fertiliser then has to do its job. Quite exciting!”
After a one-year test period Huisman des-
cribes his experiences with the Horticoop
fertilisation concept. “Compared with the
usual methods Horizon is just as expensive
and the quality of the flowers is almost the
same. Let me put it this way: the crop is
certainly no worse. And that is good. In
addition I’ve noticed a visual improvement
recently in the upper soil layer. The structure
is slowly becoming looser.” Just like Horti-
coop’s product manager for fertilisers, Peter
Klein, and account manager, Arie Verloop,
the grower also believes that there is more to
gain from the ground. That was his reason for
trying this new fertiliser concept.
At the moment the trial is only being
carried on chrysanthemum nurseries. In
addition to Huisman, the trial involves two
other Dutch chrysanthemum nurseries. “I
believe that everything succeeds or fails based
on the structure of the soil,” says Huisman.
“Therefore this concept sounds very plausible
to me: When you’re fertilising you shouldn’t
forget about the soil. Also, my advisor from
DLV Plant had a good feeling about it. As an
independent professional he closely follows
the results and he gives me the necessary
objective feedback.”
Soil availability of minerals The intention is to roll out the concept for
other product groups. Lisianthias is likely to
be the first to join the programme followed
in the long term probably by alstroemeria.
Verloop: “It’s quite strange. We claim to be
such an innovative sector, but for decades
we’ve been using the same fertilisation
strategy for many cut flowers. During the
cultivation we dose everything out of the A-
and B-fertiliser containers and provide plenty
of water but otherwise growers hardly bother
any further. The result: over dosing and a lot
of fertiliser in the drain water.” In their search
for a more efficient fertilisation method the
Text: Jojanneke RodenburgImages: Studio G.J. Vlekke
CHRYSANTHEMUMREPORT
‘Everything succeeds or fails with structure of the ground’
Innovative fertilisation concept also looks at soil condition
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Oscar Garza: “We have 60 ha, mostly tomatoes, but we want to grow to 100 ha. We also see opportunities in America and we want to be considered a
serious player.”
Investors in Mexico have just completed phase three of a newly established nur-sery that is producing cluster tomatoes, mostly for the US and Canadian market. Phase four is in the pipeline. The project began in 2010 and already covers 15 ha. The greenhouse for phase three was especially developed by its Dutch buil-ders and includes a newly designed alumi-nium gutter, durable insect netting that is integrated into the plastic cover and a new construction profile which signifi-cantly speeds up the building work.
Hydroponic Green Valley Produce is a relative
newcomer to the Mexican market. The Garza
family made the move into greenhouses just
five years ago having seen a synergy between
high tech tomato production and their gas
distribution company. With a strikingly dif-
ferent approach to traditional family produ-
cers, they immediately invested in high tech
equipment and wanted to scale-up as quickly
as possible.
Phase one was completed in 2010, phase
two in 2012 and the first plants went into the
third five-ha block in March this year. “Even
while we were constructing phase one we
were already taking into account the layout
for phase two so all the infrastructure was
based on 10 hectares,” says Edward Verbakel,
of Dutch greenhouse builder, VB Greenhou-
ses.
Top of the lineThe company cooperated with a Mexican
builder on the first two greenhouses and was
then given the contract to build the third
phase entirely. It had developed a new type of
plastic covered greenhouse, which was highly
Text: Helen ArmstrongImages: Green Valley
CONSTRUCTIONREPORT
Innovative greenhouse for high quality tomatoes in Mexico
New structure speeds construction and replacement of plastic cover
A consortium of companies, together with Wageningen UR, is developing a green-house that will maximise the amount of light entering between October and March. The goal is to achieve 10% extra yield during these months. The gain in light should come from a combination of various adjustments and improvements. Following the theoretical simulation models and physical scale models, the first winter-light greenhouse will be built next year as ‘proof of principle’ at the Innovation- and Demonstration centre in Bleiswijk, the Netherlands.
During the winter, when the natural light
level in West-Europe becomes the limiting
factor for growth and yield, the prices for
horticultural products are at their best. That’s
why growers and greenhouse builders asked
researchers to design the ideal ‘Winter-light
Greenhouse’.
Project leader Frank Kempkes distinguis-
hes three stages in their search for this green-
house concept. Firstly they needed to confirm
which features play a role and from that
calculate some greenhouse concepts. In the
second phase, researchers used scale models
of greenhouse roofs to validate the simula-
tion model and measured light transmission
when condensation (wet glass) was present.
In the last phase the ‘best’ winter-light green-
house will be built.
Effect on light transmissionThe research project is funded by Greenhouse
as Energy Source, the innovation and action
program run by sector association LTO
Glaskracht Netherlands and the Dutch Ministry
of Economic Affairs. A consortium of compa-
nies, comprising Bom Group, Glascom Horticul-
ture, Bayer Cropscience and Ludvig Svensson,
will design and develop the greenhouse. The
different consortium partners are working on
different components, such as the develop-
ment of a ‘winter-light ‘ cucumber crop that
doesn’t produce unnecessary leaves or screens
with an even higher light transmission.
“During the summer of 2014, we deter-
mined which features play a role in light
transmission in the winter when light is the
limiting factor. These include angle of the
roof, direction of the ridge, asymmetry,
arc-shaped greenhouse roofs, different types
of anti-reflective coatings, diffuse and clear
glass and the reflection value of the structural
parts in the greenhouse,” explains Gert-Jan
Swinkels, researcher greenhouse climate and
energy. Regarding the direction of the ridge, in
general a north-south direction is favourable
but during the winter an east-west orientation
is more beneficial, also with diffuse glass.
Simulation modelThe researchers varied the slope and form of
the roof: symmetrical, asymmetric or
curved. They also looked at the effect of
various AR-coatings. Most coatings increase
the transmission especially at low angles, but
in the winter it’s actually the very high angles
(greater than 60º) of incidence that are impor-
tant. The angles indicated are relative to
perpendicular. “We used these properties to
calculate a large number of greenhouse
concepts. These calculations were carried out
using a ray-tracing simulation model. This is a
realistic simulation of the transmission of light
through a greenhouse roof,” says Kempkes.
Text and images: Marleen Arkesteijn and Wageningen UR Greenhouse Horticulture
LIGHT TRANSMISSIONRESEARCH
Effect of condensation still being researched
Extra light and save energy in ideal winter-light greenhouse
Trials have been set up to measure light transmission in dry conditions. The aim is to develop a winter-light greenhouse that allows maximum
Nursery manager Remco Vijverberg sets the sensor, which hangs in the crop, to the correct gas concentration.
Ripening the last tomatoes at the end of the season is often a problem. By using a controlled administration of ethylene gas it is possible to stimulate the ripening process. Tomato nursery Van Heijningen of Maasdijk, the Netherlands, has had some good experiences with it.
Brothers John and Johan van Heijningen
grow loose tomatoes on 11.2 ha of rock wool
without artificial lighting. In this traditional,
year-round system production begins in late
February and runs through until the begin-
ning of November. Then the last tomatoes
need to have been harvested because they
start planting the new crop. Previously, to
ripen the last tomatoes, they sprayed the crop
with ethrel one week before the end of the
cultivation period.
“These ripened fruits were red on the outside
but when you cut them in two they were still
green on the inside,” says nursery manager,
Remco Vijverberg. “In terms of quality this
was not an optimal product and it was sepa-
rated into special containers by the trade. And
you had to be really careful that you didn’t
exceed the Maximum Residue Level (MRL).”
Ethylene treatmentWhile looking for an alternative to ethrel
spraying the tomato nursery came in contact
with Restrain Ethylene. This generator uses a
catalyser to convert ethanol into ethylene gas.
A sensor determines just the right concentra-
tion to use to stimulate the ripening process.
The Ctgb – the board in the Netherlands that
authorises the use of plant protection
products and biocides – granted permission
to use this gas in the Dutch tomato sector at
the end of last year.
By using a compact ‘plug and play system’
it is possible to administer a low dosage of gas
in the greenhouse during the last weeks of the
tomato crop. This ensures that the last clusters
also ripen properly. “By using this one hundred
per cent natural application a tomato grower
can harvest an extra one to one and a half
clusters per plant, without any residue,” says
Paul O’Connor, of Restrain. “Also, by adminis-
trating the gas you accelerate the ripening of
the last clusters, so the crop can finish earlier.”
This can save 0.5 to 0.75 m3 gas per m2.
ResearchResearch into this treatment with ethylene, a
natural maturation hormone, was first carried
in 2011 at the request of a nationwide commis-
Text and images: Harry Stijger
RIPENINGREPORT
Good alternative to spraying with ethrel
‘ Ethylene gives you better controlover the ripening of tomatoes’
In new greenhouses standard float glass has already made way for toughened diffuse glass with a coating. To make the most of the light gain, regular cleaning is essential. But how should you clean the glass without damaging it?
In addition to standard float glass, several
types of glass are now available for the
greenhouse roof: toughened, coated and
diffuse glass. Diffuse glass is made ‘perma-
nently’ diffuse by using rollers or etching.
Several different types of glass coatings are
available such as anti-reflective (AR), energy
saving or sun reflecting. Each type of glass
with special characteristics requires correct
cleaning to avoid losing its specific activity.
When choosing which type of glass to use
for the roof, cleaning plays an important role.
“How well and simply can you clean the
glass?” is the question always asked by Jos
Koop, project leader DLV glass & energy, the
Netherlands. “Because if a grower doesn’t
regularly clean his roof its generally 3 to 4 per
cent dirty. This light loss has a negative impact
on the yield.”
Guarantee on coated glass Regarding the choice of glass, the project
leader says, “Coated glass must withstand the
normal greenhouse conditions of moisture,
plant protection and cleaning agents, without
becoming damaged. Actually, suppliers and
glass manufacturers should provide a certifi-
cate or a written guarantee. Growers should
not have to encounter any problems with the
glass if using a coating solution for at least 15
years, the economic lifespan of a greenhouse.
If there is no certificate or guarantee the
grower shouldn’t choose that glass.”
Koop knows that condensation between
glass panes produces an etching effect. “Be-
cause there is absolutely nothing else con-
tained in condensation water it has a great
ability to dissolve substances. Therefore
growers must take care that spare glass is
stored in a dry place. Manufacturers use a
layer of white powder, such as titanium
oxide, between the panes to protect the
glass. In the past they used to put a sheet
of paper in between.”
Types of diffuse glassAccording to Koop growers can choose from
two different types of diffuse glass. The first
type is ‘prismatic’ glass into which has been
rolled small pyramids or other forms to make
it uneven. Examples of this include Vetrasol
502 and 503. The second type is micro-etched
glass, which has been roughened by using a
solvent. This type of glass is available with
a level of diffusion (haze-factor) from 10 to
90%. For a more accurate indication of ability
to diffuse light Wageningen UR Greenhouse
Horticulture developed a new value: the
F-scatter. This indicates the distribution of
the light.
Koop: “The distribution of light by the
micro-etched glass is better than that of
prismatic glass. The glass becomes dirty more
quickly and it is more difficult to clean than
the micro-etched glass. By laying the diffuse
side of the prismatic glass on the outside of
the greenhouse roof it becomes dirty more
quickly but it is easier to clean. When it’s on
the inside it becomes dirty less quickly but it
is more awkward to clean.”
Damage to glass types Solutions containing fluoride are certainly
not suitable for cleaning toughened, coated
or diffuse glass. The cleaning and etching
effect of fluoride not only dissolves the dirt
but also a miniscule layer of glass. Due to this
roughening effect the glass becomes dirty
even faster. After repeated applications the
glass becomes mat which also leads to light
loss.
With diffuse glass it is also possible to
damage the structure of the glass. Laboratory
tests on toughened glass have shown it is
affected by fluoride-containing products and
these cause a light blue haze on the glass.
Fluoride containing products irreparably
damage the coating on coated glass. Even if the
coating is on the inside of the glass, droplets
can seep through to the inside during cleaning
and damage the glass. High-pressure hoses can
also damage coatings.
Remove chalkOxalic acid or citric acid can be used as clea-
ning agents to remove dirt and chalk. These
products don’t produce any vapour and don’t
affect normal glass. Special cleaning solutions
are available for removing specific shading
products.
Glass that is coated on the outside cannot
of course be coated with a layer of white-
wash. The whitewash removers can eventu-
ally affect the properties of the coating. For
example, sodium hydroxide solution does
affect the AR-coating.
Koop: “Growers who want to whitewash
the greenhouse roof must select glass that is
coated on just one side and lay the coated
side on the inside of the greenhouse. The
outside can then be coated and cleaned later
with a remover. If the glass is clean, with a
coating on one side only half the extra trans-
mission will be achieved.”
Clean waterGrowers are advised to ask the manufacturer
or glass supplier about which cleaning pro-
ducts are most suitable to use. In addition, it
doesn’t hurt to first test a (new) solution on
both sides of one window pane. After such a
trial treatment inspect the glass for any
damage and for its clearness before conti-
nuing to use the solution. Also, it’s always
Text and images: Harry Stijger
CLEANING GLASSFEATURE
Project leader Koop warns about light loss
‘ When choosing a glass type also consider the cleaning of it’
Phytophthora is a very common genus of pathogens whose many specific species
affect both the roots and parts of the crop above ground. Just like Pythium, it belongs
to the so-called class of water moulds. The characteristic of water mould is that it lives
on organic material and as a result damages the plant. Water moulds, also known as
oomycetes, require an individual approach when using chemical control. Therefore
it’s important that the diagnosis clearly shows the cause of a certain wilting or dis-
coloration.
If plants go limp and lose their leaves in the summer then treatment rarely succeeds
in reviving severely infected plants. When Phytophthora capsici attacks sweet peppers
then the removal of diseased plants is sometimes the only option. It is recommended to
remove these plants hygienically: This requires putting every diseased plant directly
into a leak-proof bag and then transporting it to a waste container.
Plants in the vicinity of the plant that has been removed can be treated with an
anti-Phytophthora substance if necessary. In addition, it is advisable to disinfect the
area around the cleared plants to limit the spread of the fungus further.
.
Phytophthora
Text and images: Groen Agro Control
PESTS AND DISEASESIN GREENHOUSES
33-Thema22-OG-Plagen-BASIS.indd 1 28-09-15 09:41
IN GREENHOUSES NO 4 OCTOBER 201534
The photosynthetic process can hardly be bettered. But the utilisation of natural or artificial light certainly leaves room for improvement. In recent years our understanding of light has grown considerably and this has major impli-cations on how we deal with light in horticulture.
Light that falls onto a plant represents a
hefty chunk of energy. The plant can do three
things with it. First and foremost, of course,
photosynthesize: The utilisation of solar
energy for the production of assimilates.
The solar energy excites an electron in the
chlorophyll (the substance that makes the
plant green) taking it to a higher energy level.
During a whole chain of reactions it falls
back to its original level. In doing so the
trapped energy is transferred into all sorts of
chemical substances and eventually is used
to convert water and carbon dioxide into
sugars.
FluorescenceHowever, the electron can immediately
return to its lower energy level. Then it
emits light. This second effect is called
fluorescence. The plant always fluoresces
somewhat, but when this happens at a high
level something is wrong with photo-
synthesis. The plant is then unable to use the
majority of the light to produce sugars. This
happens when there is too much light, but
also if those sugars already produced cannot
be sufficiently transported away. The latter
occurs if the sugars cannot be transported
to enough places, such as developing fruits,
young buds or flowers.
The third effect of light is to heat the
plant. These three processes – photo-
synthesis, fluorescence and heating – all run
next to each other. Of course, as a grower, we
want plenty of photosynthesis because this
means production. We don’t need to worry
about trying to improve the photosynthetic
process because this is out of our control. But
because the light in the greenhouse is often
below optimum, artificial lighting is a good
way to improve production and quality.
Furthermore, there is no longer any doubt
that diffuse light improves both yield and
quality.
Photo-inhibition More light, however, is not always better.
At a certain level, photosynthesis is at its
maximum and part of the light is not utilised.
Firstly photo-inhibition occurs: The photo-
synthetic system is temporarily ‘full’,
whereby the plant not only starts to fluoresce
more, it also heats up. The situation recovers
when the light level falls and the plant
functions normally again. But at an even
higher level so-called reactive oxygen species
arise which cause irreparable damage to the
photosynthetic system.
In particular, pot plant growers are very
apprehensive about light damage and for this
reason frequently use screens and white-
wash. They tend to use light levels lower
than necessary so photosynthesis is still a
long way from its maximum and therefore
they forfeit production. However, research
shows that many shade plants can handle a
higher light level than is usual in practice
and grow much better and are available for
delivery faster. A condition is that the
humidity remains relatively high (75-80%) and
the temperature doesn’t rise too much. The
combination of a high light level, high tem-
perature and low humidity does damage the
plant.
More efficient lighting For many crops extra light offers many
benefits. With more light the plant makes
more sugars. This larger reservoir of sugars
eventually results in the plant making more
side shoots and more flowers. Setting is also
better.
Text: Ep Heuvelink, Tom Dueck, Filip van Noort (all at Wageningen UR) and Tijs KierkelsImages: Jan van Staalduinen and Philips
Plant can use a lot of light
Production very closely linked to amount of intercepted light
Much research has been carried out in recent
years on diffuse light and the results all point
in the same direction: Diffuse light is better
than direct light; yield increases.
Figure. The photo response curve
Light is used more efficiently if the leaves share the available light, such as under diffuse glass.
By using a double screen tomato grower Gertjan van der Spek hopes to end with gas consumption of 27 m3.
Gertjan van der Spek is the first grower in the Netherlands without supplemen-tary lighting to install two transparent energy screens without any dehumidifi-cation system. This is his next step towards saving energy having already reduced the use of the minimum heating pipe and ventilating above the screen, instead of making gaps in the screen. In this way he hopes to use less than half a cubic metre of gas per kilogram toma-toes.
The idea of a double energy screen in vegeta-
ble production is not new. A growing number
of pepper growers are choosing this option.
“Pepper plants grow less quickly. Therefore the
screens can remain closed for longer. For them
the switch to two screens is not so great,” says
climate specialist Paul Arkesteijn, of screen
manufacturer Ludvig Svensson.
To show that this offers possibilities for
tomato growers too, a demonstration trial has
been running at the Improvement Centre in
Bleiswijk, the Netherlands, over the last year.
The trial compared the results in an area with
two moveable transparent screens with a
control that had a transparent screen with a
fixed anti-condensation film.
The upper screen was a normal Luxous
1347 FR transparent energy screen and under-
neath was a 1347 FR H2NO with anti-conden-
sation activity: This latter screen spreads out
the droplets of condensation. According to
Arkesteijn both transmit 80% light and when
both are closed they transmit just 64% light.
The crops in both greenhouses grew well. The
trial greenhouse saved an extra 4 m3 gas/m2 of
energy.
More savingsGertjan van der Spek, of Solyco, which has two
units in the west of the Netherlands, grows
Roma-tomatoes on 4.3 ha. He belongs to a
group of six nurseries that together form a
horticultural cluster. They have a joint boiler
house that has access to three energy sources:
Waste heat from the ROCA-central; two com-
bined heat and power (CHP) generators; and
a boiler, which serves as back-up if there’s a
break-down in the supply of OCAP-CO2.
“Within the cluster we want to invest in a
heat pump to further cool the flue gases from
the CHPs. The flue gases are currently 45 to
Text and images: Marleen Arkesteijn
DOUBLE SCREENREPORT
Tomato grower Van der Spek makes distinct choices
No lighting, but still two energy screens without dehumidification
Shelters for predatory mites As part of the project ‘standing army’ we are looking at
possible ways to improve the establishment of predatory
mites. It is very clear that lack of food is often a problem
in ornamental crops. This can be overcome by providing
extra pollen or other food sources.
However, even in crops where an excess of food is
offered, the predatory mites do not always become well
established. In a trial with pot plants it was found that
the density of predatory mites was ten times higher in
spathiphyllum than in anthurium, even when a similar
amount of pollen was added to both plants. The possi-
ble reason is that when the air humidity is low, spathi-
phyllum offers more shelter as it has a better micro-
climate than anthurium.
On some plants these shelters, so called acarodo-
matia or ‘predatory mite houses’, are very clearly present.
Often they are dense clusters of leaf hairs on the area
where leaf veins come together (see photo). These
domains provide a better microclimate as well as offer
protection against the predators of predatory mites.
39IN GREENHOUSES NO 4 OCTOBER 2015
WAGENINGEN UR GREENHOUSE HORTICULTURE
For more information please contact: José Frederiks, office managerWageningen UR Greenhouse HorticultureTelephone: +31 317-483878Email: [email protected]
Mushroom compost works against root knot nematodes
Horticultural training for greenhouse systems in Rwanda
Root knot nematodes are a problem in the organic
production of fruit vegetables. A trial is being carried
out in Bleiswijk together with organic growers to test
measures for the propagation and cultivation of
tomatoes.
Five litre pots were filled with soil from the growers.
The research focused on various types of compost,
additives such as silicon as well as antagonists to root
knot nematodes. The measures were tested separately
and in combination with each other to see if it was
possible to achieve a synergetic effect. Woody compost
and mushroom compost with silicon in particular were
able to reduce the number of root nodules on the roots.
Woody compost also resulted in a reduction in the
number of offspring. However, adding the fungus
Trichoderma was counter-productive and reduced the
suppressing effect.
The combination of mushroom compost and silicon
also reduced the number of root nodules. The effect
was stronger when the products were given together
than when each was given separately. Use of mushroom
compost also resulted in a larger (heavier) tomato plant.
Mushroom compost does need to be applied carefully
because the material is ‘sharp’ and can damage the roots.
Together with a number of Dutch companies and
research institutes Wageningen UR Greenhouse
Horticulture is taking part in the SMART-programme.
The project focuses on Africa and has already organised
demonstrations and training for greenhouse cultivation
systems at different levels of technology in Rwanda and
South Africa.
Rwanda is a country with a suitable climate for green-
house production and has a strong, growing interest
in covered cultivation. Together with Rijk Zwaan and
Koppert, training has been organised for managers and
staff of the RwandaBest Company who are preparing for
the first crop in a new greenhouse built by Bosman Van
Zaal and equipped by Hoogendoorn.
Covered cultivation in Rwanda is still at a low level
in terms of technology, cultivation technique, production
and product quality. Issues such as plant care, water and
nutrient supply, crop protection and marketing can still
undergo much improvement. There is, however, a
reasonable demand for good tomatoes in supermarkets
and hotels but these customers expect continuity and
good quality.
Water cultivation of iceberg lettuce in cabrio greenhouse
The production of iceberg lettuce and other types of
lettuce on water cultures in Bleiswijk is progressing
well. Lettuce is growing in two plastic greenhouses on
the Dry Hydroponics system. During the winter LEDs
provide supplementary light during the day.
As the weather turns warm, the roof and sidewalls
of this greenhouse can be fully opened. It is being
investigated whether iceberg lettuce can be grown year
round in a sustainable way and still maintain a good
quality. Certain customers, such as processors,
increasingly require a year round supply of a product
with a consistently high quality.
By increasing the planting density from 20.8 to 25 plants
per m2 (+20%), the weight of the heads of various types
dropped by 10%, but the total number of kilos increased
by 8%.
Compete Plus is added to each container on a
monthly basis. This increased the harvest in February,
March and April by 15, 5 and 0% respectively. Thus the
effect decreased with time. With more artificial light,
together with a higher greenhouse and water tempe-
rature, the lettuce grew faster in winter. The water was
heated to 15 or 17ºC, depending on the light intensity of
the artificial light.
39-Thema21-WUR.indd 1 28-09-15 09:45
IN GREENHOUSES NO 4 OCTOBER 201540
Pests such as insects, mites and nemato-des don’t just cause damage, in the case of quarantine pests they can also limit exports. In cooperation with the sector, entomologist Yutong Qiu tested the possibility of using Controlled Atmos-phere Temperature Treatment (CATT) in the post harvest phase to control these pests in a non-chemical way. Within the short term this approach is expected to successfully control Tuta absoluta in tomatoes and thrips in chrysanthemums and peppers.
The ‘controlled atmosphere’ (CA)-technique
is already widely used during the storage of
fruit and vegetables. Heat treatment is another
technique currently used. The CATT-method is
a combination of both, in which the composi-
tion of both air as well as temperature can
vary. By applying an atmosphere that contains
a low level of oxygen and more carbon dioxide
at a slightly raised temperature, the aim is to
kill the pests within a few hours to a few days
while preserving the product.
Standard treatmentThis method was developed for the environ-
mentally friendly disinfection of propagation
material for strawberries against strawberry
mite when disinfection with methyl bromide
was banned. The strawberry mite is control-
led while the plants remain in good condi-
tion. Strawberry growers now use this as a
standard treatment.
Carbon dioxide and oxygen are gases that
are normally present in the air so the CATT-
treatment is regarded as non-chemical and
therefore does not require special permis-
sion. The method is included in the Elite-
certification for strawberry plants. In the
meantime two companies in the Netherlands
are applying this method of disinfection to
the whole sector.
Four parametersThe next step was for researcher Yutong Qiu,
and colleagues at Applied Plant Research (PPO)
in the Netherlands, to see if was possible to
apply this non-chemical approach to quaran-
tine diseases. In one of the projects financed
by the Dutch Ministry for Economic affairs
they screened, in close cooperation with
Wageningen UR Food & Biobased Research,
ten different quarantine pests. The project
ran from 2012 until the beginning of this
year.
Text and images: Marleen Arkesteijn
PLANT HEALTHRESEARCH
CATT shows promise against quarantine pests
Short term non-chemical approach to Tuta absoluta and thrips
Screening for the ideal atmospheric conditions is taking place at Wageningen UR Food & Biobased Research where there is a range of 64 ‘mini’
Careful watering is very dependent on the possibilities within the nursery. When things go wrong you may find the last six rounds of watering have accu-mulated in the irrigation hose. That happens just as easily in large or small systems, discovered researcher Chris Blok. You can already take this into account when installing a new irrigation system.
A trial is being carried out in the greenhouses
at Wageningen UR Greenhouse Horticulture
on irrigation systems for sweet peppers. This
research has been set up with water specia-
list, Revaho, and is testing the speed of the
watering systems within closed cultivation
systems. Researcher Chris Blok and product
specialist Stefan Bakker explain why it is so
important to know what happens in the
dripper pipelines and within the drippers
and why it is so difficult to calculate this
well. The period of time that the solution
containing fertilisers or crop protection
substances remains in the pipeline is much
longer than you would expect.
Loss of speedThe time it takes for the water to flow past
the first dripper to the moment it reaches the
last plant is called the ‘travelling time’. Sup-
pliers of irrigation systems have a special
calculation program for this. As long as the
water is still in the main pipeline it is possi-
ble to calculate exactly how long it takes
from the fertiliser unit to the first dripper. Up
to that point the flow rate remains the same.
Once the nutrient solution reaches the
first dripper part of the solution enters the
dripper for the first plants, the rest continues.
Each time a little amount of water leaves the
pipeline as it enters the next dripper the
speed of water flow slows down. And as the
amount of water continually decreases the
time it remains in the pipeline as it approa-
ches the end increases.
This problem doesn’t just happen on nur-
series with long paths, it happens indepen-
dently of the length. However, there is a
relationship between the resistance in the
pipe and the path length but this effect
cannot be calculated.
Six rounds of watering When administering crop protection pro-
ducts, you want the substance to act on the
roots all night long. A contact substance
needs to remain at the roots for as long as
possible. Therefore you supply that in the
last irrigation of the day. A systemic subs-
tance is applied at the start of the day to get a
good take up through the process of transpi-
ration.
Meanwhile Chris Blok has been able to
show that it certainly takes six rounds of
watering before the substance reaches the
last dripper (of standard size). If you supply
the substance in the evening then it doesn’t
take much explanation to realise that the
substance will arrive a day later. Most sub-
stances still work then but the contact period
is much too short because new rounds of
clean water arrive shortly afterwards. If, for
example, you supply 0.25 litres per m2 per
day in the winter, then it can take 17 days
before the last point is reached.
Delay and decomposition Stefan Bakker: “Therefore you need to take
into account that the water flows through
the nursery in waves.” As a result of measure-
ments taken in the greenhouse, a model has
been created which predicts how the water
is distributed.
It’s the same principle when raising or
lowering the EC in greenhouse vegetable
production based on light. Many growers
think that they are having a direct impact but
even in the summer it can take hours before
the correct EC reaches the last point. Add that
to the fact that these plants are less visible,
the grower notices far too late that his treat-
ment makes little sense. Stefan Bakker: “That
is also the reason why we install many sys-
Text and images: Pieternel van Velden
DRIPPERSFEATURE
Specialists advise about sensible watering:
‘ Avoid delay when distributing fertilisers and crop protection agents’
Stefan Bakker (left) and Chris Blok: “As a grower you need to take into account that the water
André van Paassen (right) with Tom Zwijsen (left) and Arie Verloop: “You’re rid of all the thrips that you catch early by sweeping and so you don’t
need to spray them.”
The Dutch nursery Arcadia Chrysanthe-mum, of Kwintsheul, has been working with the so-called ThripsSweeper since September. It is a suitable and effective solution with which to catch adult thrips in a chrysanthemum crop. The idea for this innovative device arose during a brain storming session with growers and it was further developed together with them.
Thrips is the biggest problem in chrysanthe-
mum cultivation. The thrips’ pupae and larvae
can be controlled with natural predators such
as nematodes and predatory mites. Adult thrips,
which can transfer viruses and damage flowers
by pricking them, cannot be well controlled
due to the lack of substances available. Many
growers use mass trapping – a sticky trap for
every ten square metres – in order to get rid
of them. This method works well but doesn’t
catch all the adult thrips because the traps are
stationary. To catch even more thrips, the idea
arose to automatically shake them out of the
crop and simultaneously move the sticky traps.
Crop in motion“The idea, that was thought up on a Friday
afternoon, was developed into a device that
moves the crop. As a result the thrips jump
out and are easier to catch. Simple, but effec-
tive,” says Tom Zwijsen, manager cut flowers,
of Horticoop.
The supplier’s technical department
developed a construction that can be moun-
ted under an existing spray boom. Rows of
sticky traps and rubber tubes hang from the
aluminium frame. The tubes are weighted
so that they hang straight down and produce
a tapping effect within the crop. When the
tubes move through the crop they shake the
thrips, as it were, awake. With a fright they fly
up and hit the sticky traps that are following.
The colour of the sticky trap, yellow or blue,
is less important because it’s the shock that’s
effective. The traps do need to be replaced
after four weeks.
Optimal catch results Different types of tubes have been tested in
the chrysanthemums. If the material is too
stiff, it can damage the crop. A flexible tube is
best, so that it also doesn’t get caught behind
the supporting gauze. The tubes that go
through the crop are longer than the sticky
traps; the sticky traps need to remain above
the crop and not touch it. The settings for this
Text and images: Harry Stijger
INNOVATIONREPORT
André van Paassen, chrysanthemum nursery Arcadia:
‘ Innovative device is extra tool in fight against adult thrips’
The grower who wants to provide his substrate-based crop with precisely the right nutrients will be better off forget-ting the nutritional formulas. If you want to do it better you should from now base it on analysis of uptake by the plant. This is much more accurate. The potential gains from this method will grab most growers’ attention: Better control over vegetative and generative growth, efficient use of fertilisers and more kilograms.
Analysis of plant uptake is at best considered
a hefty calculation involving a number of
factors. These are the mains water and its
composition, the drain water and its compo-
sition, the measured amount of water uptake,
the measured CO2 level, the volume of drain
water and the radiation. When the sum has
been properly worked out then you know on
one hand which nutrients have been taken
up by the fruit and on the other hand by the
plant’s green material. The calculation can be
worked out for every element.
Well-known pitfallThe inventor of the system is Ruud Kaarsema-
ker, project leader at Groen Agro Control,
Delfgauw, the Netherlands. Meanwhile
around 60 nurseries are using this systematic
method. It was created as a result of questi-
ons posed by commercial growers. “It was
already known that cultivating based on a
nutritional formula was not always very
accurate. By accuracy we mean: The plant
receives what it needs. Growers started to
ask themselves if something could be done
about the inaccuracies.”
He gives the following example: “Research
with peppers has shown that a high level of
the element boron in the slab doesn’t always
equate with sufficient boron in the plant.
When considering the slab you’d assume that
too much boron has been supplied. You’d be
tempted to reduce the dosage, something that
often happens in practise. But because the
plant has a shortage and apparently has taken
up too little, you should at least continue
with the high dose. This example illustrates
the well-known pitfall: what the slab tells
us is not automatically the reality in the
plant.”
Five factorsWith help from uptake analysis the nutrients
can be supplied much more accurately. Accu-
racy is based on a number of factors. Kaarse-
maker has made a list:
1. The uptake by the crop responds mostly to
concentrations in the irrigation water. If
the composition of this changes the uptake
by the crop changes almost automatically.
2. The concentration in the slab is mainly the
result of what the crop has taken up. If the
concentration in the slab remains high
then the plant has taken up very little. If
the concentration is low then in general
the plant has taken up a lot.
3. The difference between the dose and the
uptake often provides a better picture of
the nutritional status than the concentra-
tion in the slab.
4. Anyone who adjusts the nutrients based on
the concentration in the slab is driving the
plant in completely the wrong direction.
The nutrients are corrected the wrong way.
The example mentioned previously with
peppers and boron makes this very clear.
5. By adjusting the nutrition based on an
analysis of the uptake, the dose is much
more accurate and swings in the nutrient
solution are much smaller.
Steer vegetatively or generatively?Analysis of uptake can bring advantages to
many nurseries. One important positive
point is that the grower is able to better steer
the crop towards vegetative or generative
production. He can achieve this using the
ratio between sulphate and chlorine with
nitrate. Early on in the cultivation he has to
supply relatively more sulphate and chlorine
than at the end of the production to realise
the same amount of generative growth.
“If the grower wants to know exactly how
much of each element he needs to supply,
there’s more chance of him achieving this
with uptake analysis than with a traditional
nutritional formula. Every grower asks himself
how he can bring his crop into just the right
Text and images: Jos Bezemer
ANALYSIS OF UPTAKEFEATURE
Analysis of crop uptake replaces traditional nutritional formula
What the slab says is not automatically the opinion of the plant
Ruud Kaarsemaker in the research greenhouse: “The largest gain is the potential extra yield.”
Dirk Aleven: “In Georgia we are growing batavia, lollo rosso, lollo bionda, romano, salanova and rucola with an average head weight of 130 gram.”
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Dutch entrepreneur Dirk Aleven lives in Georgia. His company has a glasshouse of 6,000 m2 in which 3,600 m2 are used to grow lettuce. “Our greenhouse is comparatively small but we grow lettuce on water. Then it’s a lot. With an annual turnover of 1 million heads of 130 gram each we can supply the entire country with lettuce.”
The company FoodVentures has set itself up
in countries such as Georgia and produces for
the local market. Entrepreneur Dirk Aleven
explains: “There is a large demand for quality
vegetables in this country. The young gene-
ration is no longer interested in farming and
is migrating towards the towns. In the super-
markets they want to be able to buy all sort of
vegetables all the time.”
Vegetables are mostly grown in the open
field so local producers are dependent on the
weather. During the months of April, May and
June they grow plenty of vegetables and for a
few months they are in abundant supply. Du-
ring the other months there is a large shortage
of fresh vegetables. To overcome the shortage,
the country imports a lot from Turkey and
Iran. However, the quality of these vegetables
is poor. Aleven saw an opportunity: “Georgia is
a small market, but one that demands quality.”
A few years ago he didn’t expect to be
living here now with his family. “I started a
world tour on my motor bike travelling from
the Netherlands to Nepal. In Georgia I got tal-
king to some local businessmen about green-
houses.” At that point his company had no
plans to build in Georgia but it was already
in the process of building a greenhouse in
nearby Ukraine.
Garnish for dishes“In Ukraine we had many economical and
political set-backs. As a result the nursery
opened in 2015 instead of the planned 2013,”
explains Aleven. “By comparison, in Georgia
the construction went very fast. We started in
June last year and opened in December. At the
moment we are ahead of schedule.” But in
Georgia things aren’t easy either. The inhabi-
tants know lettuce but mostly as a garnish to
dishes. It is hardly ever a main part of the
meal. Therefore the market still has to be
developed. It’s a question of promotion and
waiting.
Nevertheless, the entrepreneur is positive.
“We are just starting. Our strength lies in the
continuous quality we offer. We sell high-
quality lettuce which appeals to the restau-
rants.” With a turnover of one million heads
per year the company can supply the entire
country with lettuce. The lettuce varieties,
batavia, lollo rosso, lollo bionda, romano,
salanova and rucola with an average weight
of 130 gram, are grown in an area of 3,600 m2.
“We now have sales of 1.5 tons per week. The
maximum that we can achieve from this
Dutch teach local producers how to produce more effectively
‘ I want to help growers, I don’t need to own the largest greenhouse in Georgia’
Save on water and fertilizers by recirculating drain waterHortiMaX has launched the latest development in water disinfection with low pressure UV technology. Our new HortiMaX VitaLite E-series allows you to reuse your drain water safely and reliably without adding chemicals.
Save on water and fertilizersReusing your drain water will not only benefit the environment, but will also save you money. Depending on your individual needs, our VitaLite disinfection unit will provide a full return on investment within 2 to 3 years. Call us now, so we can calculate your ROI.
No chemicals addedWater disinfection using UV radiation is the safest technology available today. You don’t need to add chemicals to your drain water, which can accumulate in your recirculation system. This means no chemicals can be passed on to your crops, making it safer for your plants.
Reliable, safe and controlledOur VitaLite unit is equipped with sensors that continuously monitor the water flow rate and applied UV levels. The HortiMaX controller ensures that your drain water is treated with the most effective UV dosage and efficiently manages the water flow between your drain water tanks.
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NEWExtra introduction discounton the �rst 10 units
The Danish Stål & Plast has been manufacturing Ebb & Flow bench trays in high impact polystyrene since 1984. Recently the company has expanded its product range with larger dimensions. Today they offers these trays in all sizes up to 1720 x 6200 mm. Uniformity, high quality and short, reliable delivery times are keywords for these products.
Over the years, the bench trays have been thoroughly tested for use with fertilizers, effects of temperature change, UV radiation and general daily wear in a modern greenhouse. This knowledge is used for continuous improvement and to optimize the products, so that today they represent the industry is absolute best quality.
The bench trays are manufactured on modern automatic vacuum forming machines. The production facilities are operated mainly by robots which are supervised by specially trained personnel with many years of experience.
Today the comprehensive bench tray system is sold through a worldwide network of distributors. Distributors are typically greenhouse construction companies who install the trays as part of a turnkey projects as purchased by nurseries.More info: www.staal-plast.dk
Clip prevents tearing of topped tomato plants
Tomato plants that have been topped run the risk of tearing in the axil. As the growing stems become heavier the plant is vulnerable to splitting. It can amount to hundreds of plants per hectare with axil damage, resulting in unnecessary growth inhibition
A solution is the Twinhook, a ‘double clip’ made from plastic which provides the axil with exactly the support it needs to prevent damage. According to supplier Royal Brinkman the clip can be attached very quickly and easily due to its clever design. It is recommended to attach the clip within one month after planting.
Growers have been searching for solutions to prevent tearing for a long time. Many have tried providing the plant with more support by twisting two clips together. However, this is laborious and labour intensive. The need for additional support depends on the variety; some varieties always produce heavier plants or are weaker by nature and tear more readily. It also appears that crops with supplementary lighting are more likely to tear. More info: www.brinkman.com
Concept for self-build conveyor systemsTrexx Modular Conve-yors is a patented new system that allows users to quickly and easily build a conveyer system themselves. The concept has been developed by Jonge Poerink Conve-yors, specialists in conveyor systems.
The design is based on a modular building prin-ciple with lightweight parts made from polyethylene. In addition, an assortment of compatible components is available. Thanks to the modular approach it is flexible and offers unlimited expansion possibilities. The installation, customisation and dismantling require no special skills, tools or assembling.
The construction parts can be made to any length and are available in straight or curved versions. This makes it possible to create bends and thereby best utilise the available space. More info: www.trexx.com
Solution for preventing iron deficiencySupplier Van Iperen has launched Fervent Duathlon, a new product against iron deficiency. It has a unique composition and is suitable for open field, pot and substrate crops.
According to product manager Gert-Jan Dillo of The Dutch company in Westmaas, it’s the special composition of the pro-duct that makes it effec-
tive. “The unique combination of EDDHA- and HBED-chelates makes it a particularly effective product. The EDDHA-chelates provide fast initial activity for the plant. In addition, the HBED-chelates ensure long-term availability in the root environ-ment.”
The product offers several other advantages. The iron is easily taken up even at a high pH. In addition, the new product is completely soluble and leaves behind only a minimum residue in the fertiliser container. Van Iperen says this introduction is a new solution for combating iron deficiency. The product is available in 5 kg bags.More info: www.iperen.com
New propagation block gives plant more body
Tomato growers who use the new Rootmaxx-propagation blocks from Cultilene are positive about their experiences. Kees Stijger, of Honse-lersdijk, the Netherlands, switched over comple-tely to the new blocks in one go. The fact that the
roots are contained in the block particularly appealed to him. “Roots on the underneath of the block are simply lost. The block is fully developed with roots, with more roots than in other blocks, but less on the underside of the block. You don’t want them there. I am very pleased with what I have seen so far.”
Rick van Vliet of CombiVliet, Maasdijk, says his trial with the blocks was also successful. “During the trial we quickly saw what we wanted to see and we know what can be achieved. A plant with more body.” According to Saint-Gobain Cultilene, these are the strongest blocks with the roots remaining within the block and not on the underside. More info: www.cultilene.com
The news items on this page are provided by suppliers. The editors are not responsible for the content.
First Agrobío bumblebee hives supplied in Turkey
Recently the first bumblebees, produced at the new Agrobío production facility in Antalya (Turkey) were supplied to various tomato growers in the
region. The opening of this new production facility gives growers in Turkey a quicker access to bumble-bees and beneficials. The Spanish company is partly owned by Royal Brinkman.
Bumblebee hives of Agrobío are known as highly active pollinators. The company breeds two types of Bombus terrestris (the large earth bumblebee); a regular and a special summer hive, suitable for use in both glass and plastic greenhouses. An extra ventilation system in the summer version makes them suitable for high-temperature conditions. They also provides solutions based on the use of bumblebees in outdoor crops. Those hives are protected against climate influences by a special insulated package.More info: www.brinkman.com
Compact version of double-lipped truss clamp
In the 1990s Van der Valk introduced the stainless steel truss clamp. Several years ago the company introduced a new, improved version and
demand has dramatically increased recently. This is because this model has a double lip that provides better support for the polyester cables. Thanks to its compact design, less material is needed, so there was no need to increase the price.
The two rounded lips on the clamp prevent the polyester cables from becoming damaged. Truss clamps with one lip carry the risk that, if the lip is inadvertently bent, the polyester cable will be damaged. The truss clamp with a double lip is just 26 mm wide so is very compact. It is available in different sizes, to suit different systems. More info: www.valksystems.nl
Magnesium important building blockThe nutritional element magnesium (Mg) is an important building block for the growth and flowering of plants but it is also a very impor-tant mineral for the health of people and animals. According to
Jaap Brink, of Brink Business, agent for potassium and magnesium producer K+S KALI GmbH, the essential role of magnesium in fertilisation is often underestimated.
Magnesium plays none or hardly any part in the fertilisation recipes yet the element makes a decisive contribution to yield and quality improvement of a crop. Magnesium is essential for many functions, not only for the production of chlorophyll. A deficiency of magnesium doesn’t only occur if the magnesium level in the soil is low. Dry periods and an unbalan-ced fertilisation strategy also can cause magnesium deficiency in crops. A grower doesn’t always realise that, says Brink.
Not only magnesium, but also elements such as sulphur, boron, manganese and zinc deserve more attention with respect to fertilisation. Products in the company’s EPSO-line comply fully with this requirement. More info: www.brinkbusiness.nl