1. How to obtain a high tomato yield
100 kg per m2 per year or more ?
Ep Heuvelink
Horticultural Supply Chains, www.hpc.wur.nl/uk
Ep.heuvelink@wur.nl
Plant Sciences Group, Wageningen University
1st Agriconference on Tomatoes from Morocco
9 December 2009, Agadir, Morocco

2. Yield development (Netherlands)
Sweet pepper
Cucumber
Tomato
+ 96%
+ 117%
+ 34%
Sweet pepper
Cucumber
Tomato
0
20
40
60
80
1980 1990 2000 2010
Year
Yield(kgm
-2
)
+107%
+94%
+125%
Cucumber
Tomato
Sweet Pepper
Tomato in Morocco
(Kwantitatieve Informatie voor de Glastuinbouw (KWIN 2008))

3. What factors are important for high yield ?
Greenhouse technology (e.g. light transmission)
Cultivation techniques (e.g. high wire system, rootstocks)
Modern cultivars
Greenhouse climate control
(temperature, CO2, humidity, supplementary light)
Most recent developments
(semi~closed greenhouses, diffuse light)

4. Also important is:
High education level of growers
Moderate climate:
winters not too cold, summers not too hot
North
Northsea
sea

5. Obtain high light transmissivity of the greenhouse
1% more light ≈ 1% more yield
Greenhouse transmissivity in 1980 ≈ 65%
nowadays ≈ 78%
represents about 20% yield increase
Large glass panes, small construction parts, white !

6. Cultivation techniques
High wire system; same plant almost year-round
Long season, up to 50 weeks; no production gaps

7. Cultivation techniques
Stonewool + drippers; better control of root environment
Extra stems in summer (2.5 plants m-2 ￫ 3.8 stems m-2)
Use of grafted plants (cultivar on rootstock)
StonewoolStonewool
CubeCube & Slab& Slab

8. 0.0 1.0 2.0 3.0 4.0
Leaf Area Index
0.0
0.2
0.4
0.6
0.8
1.0
Fractionlightintercepted
y = 1 - e -k LAI
Influence of Leaf Area Index (LAI) on the fraction of light intercepted
by a tomato crop (k = extinction coefficient = 0.8)
LAI: mLAI: m22 green leaf area per mgreen leaf area per m22 ground area)ground area)

9. Measured LAI throughout the season for tomato
(measurements at modern commercial farms)
0
1
2
3
4
5
50 100 150 200 250
Day of year
LeafAreaIndex(m2
m-2
)
Year 2003
Year 1990
Now much higher than in early nineties, probably because
extra side shoots are retained from spring onwards + rootstock?

10. Effect of cultivar on tomato yield (Spring crop)
40% yield increase since 1950, mainly because of higher light use efficiency

11. Greenhouse climate
Modern climate computers make
more accurate control possible
Important factors:
temperature, CO2, humidity

12. • Heating
→ boiler + hot water pipes
• Cooling
→ vents in roof
→ fog cooling
→ roof cooling
Production techniques in modern greenhouses (1)Greenhouse climate: temperature

13. Fruit weight (dry mass) and
fruit growth period (FGP) tomato
Temperatuur (oC) Gewicht (g) Uitgroeiduur (d)
17 4.8 74
19 4.3 63
21 3.2 56
23 2.7 50
Source: A.N.M. de Koning
At lower temperature harvest starts later and
fruits are more heavy
Temperature (oC) Fruit weight (g) FGP (d)

14. High temperature stress (tomato)
No effect on total growth
Poor fruit set
Cause: bad pollen, poorly released 0
4
8
12
16
Controle Hoge Temp
Aantalgezettevruchten
perplant
0
20
40
60
80
100
Controle Hoge Temp
Levendestuifmeelkorrels
(%)
Control: 28/22oC D/N; High temp. 32/26oC
Source: Sato et al. 2006
Questions like: is 1 h 36oC a problem?
Or: Is 1 h 38oC same as 10 h 36oC?
Not yet clear !
Control High temp.
Control High temp.
Viablepollen(%)
Numberofset
fruitsperplant
AlsoAlso tootoo lowlow temperaturestemperatures limit fruit set !limit fruit set !

15. Greenhouse climate: CO2
Natural gas for heating: flue gasses for CO2
Pure CO2
Source: E. Nederhoff

16. Rule of thumb for CO2 effect:
For each 100 ppm increase in CO2 % increase in growth can be
calculated as
1500 × 1000
CO2 × CO2
From 350 to 450 ppm: 12% growth increase
From 600 to 700 ppm: 4% growth increase
From 1000 to 1100 ppm: 1.5% growth increase
But from 350 to 250 ppm: 19% reduction in growth!!
Source: E. Nederhoff, 1994

17. Greenhouse climate: High humidity
Deficit < 0.2 kPa (<1.5 g/m3) or RV >94% at 25°C
Too low Ca in leaves ĉĉ> smaller leaves ĉĉ> less light
interception ĉĉ> less photosynthesis
Pollination less optimal
(without bumble bees)
Higher disease risk (botrytis)
Higher risk fruit “disorders”
(cracking)

18. Greenhouse climate: Low humidity
Deficit > 1 kPa (>7.5 g/m3) or RH < 70% at 25°C
Water stress in plant
Stomata close
Cell elongation reduced ĉĉ> smaller, thicker leaves
Less photosynthesis
Reduced water content fruit
Blossomĉendĉrot (BER)

19. New trends: semiĉclosed greenhouse
AirAir--conditioned (active cooling) so vents more closedconditioned (active cooling) so vents more closed
Too high temperatures can be avoidedToo high temperatures can be avoided
Higher COHigher CO22 levelslevels higher yieldshigher yields

20. In the Netherlands: Winter: 80% diffuse radiation
Summer: 60% diffuse radiation
Advantages of diffuse radiation:
More even distribution of light (horizontally; no shadows)
Light penetrates deeper in the crop
Lower risk of light saturation
Mild micro-climate
New trends: Diffusing cover materials

21. Control Low diffuse High diffuse
Haze 0% 30% 70%
Transmission 83% 83% 80%
New trends: Diffusing cover materials
Experiment with cucumber crop: Bleiswijk 2008,
Netherlands

22. Diffuse light: 9% higher cucumber production
(crop planted in March)
0
25
50
75
12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Weeks
Cumulatiefproductie(kg/m2)
Hoog diffuus
Laag diffuus
Controle
+9.2%
+6.5%
Weeks
Production(kgmĉ2)
Source: T. Dueck
High diffuse
Low diffuse
Control

23. Conclusion: main reasons for high tomato yield
Almost yearround cultivation
(high wire system, extra stems in summer, rootstocks)
Cultivation out of soil
Hightech greenhouses (high light transmissivity,
good temperature and CO2 control)
High yielding cultivars (breeding)
Future developments:
semiĉclosed, LED lights

24. Thank you for your attention
The following colleagues contributed to this presentation:
Menno Bakker, Silke Hemming, Leo Marcelis, Anke van der Ploeg