Optimizing greenhouse climate in tomatoes by André Kool, Green Q

Content Why focus on climate? What is a good greenhouse climate? -Day-climate -Dissimilation -Night-climate 24-hr average temperature regulation Speed of growth Conclusion

Important subjects to check 1.Crop parameters (tomato) -Stretching of internodes, leafs, truss-stem -Colour of leafs (head) and fruits -Power of head and truss -Pollination and fruitsetting -Production and quality -Presence of diseases (f.e. botrytis) 2.Greenhouse parameters -computer settings (basic settings & strategy) -realised climate, irrigation, fertilisation, CO2 -”feel” the climate

Why focus on climate? 1.Most problems with quality and production are caused by a bad greenhouse climate: too small fruitsize (too less kg’s!!!) fruitskin problems (cracking) botrytis and other fungi-problems Most problems can be prevented by optimizing greenhouse climate!!!!

More reasons to focus on climate Irrigation and fertilisation are blamed for many problems…………………… Irrigation and fertilisation are important, however……a good greenhouse climate enables the crop to take up water and nutrients. Water and fertilizers are taken up by evaporation of the crop. evaporation of crop is affected by greenhouse climate…………….

Still more reasons to focus on climate Cultivar is important, but many times blamed for problems undeserved. In many cases “bad” properties of a cultivar can be (partly) reduced by optimizing climate. Especially fruitskin problems

What is a good greenhouse climate? Before answering this question first some basic plant physiology Photosynthesis=assimilation=production of sugar=growth Only take place during day time (sunrise-sunset) A good day-climate is the most important factor for a optimal growth.

Bruto fotosynthesis Bron: D. Klapwijk At high light level At low light level Bron: D. Klapwijk

Dissimilation dissimilation Bron: D. Klapwijk

Netto fotosynthesis dissimilation Bron: D. Klapwijk

Day-climate? (1) Day-climate (General definition): A optimal day-climate is a perfect combination of: Temperature Light Humidity CO2

Day-climate (2) To optimize climate in greenhouse the grower should react on: 1.Outside weather conditions 2.Greenhouse properties & facilities 3.Crop properties (tomato)

Day-Climate (3) Outside weather conditions Wind (speed and direction) Lightlevel (radiation) Temperature Rain Snow Cloudiness

Day-Climate (4) Greenhouse properties & facilities height light tranmission greenhouse roof (glass+construction) heating capacity (boiler+pipes) insulation (loss of heat and humidity) position of heating-pipes growing on a gutter ventilation capacity screens (% heat saving) CO2 dosage-capacity (kg/ha/hr)

Crop properties (tomato) Day-Climate (5) Crop properties (tomato) Stem density, distribution of stems Cultivar Plant-load Pepino-virus

Day-Climate (6) Optimizing greenhouse climate is complex because of many variables It’s difficult to give concrete (absolute) figurs (f.e. temperatures) Consider all mentioned figurs in this lecture as “indicative” and not as “absolute” The big point is how to interprete the figurs to your specific conditions Watch your crop. The plants are always telling the truth!!!

Day-climate(7) Morning Sunrise the crop must be heated up sufficient (17-19°C) Sunrise (lowest outside temperatures!!) Too cold heads in the morning (especially in combination with ventilation) is a major cause of problems: -Botrytis -Small fruitsize -Fruitskin problems (cracking, cold head warm roots) Plant physiological process involved: -stretching process of plantcells -evaporation process (transport of water,nutrients,assimilates) -condensation risk (physical process)

Morning A “bad” colour in the head is typical for cold heads Charactaristic is too short internodes and too thick stem Heating up the crop in the morning can be finetuned with sensors like: -plant temperature meter ( T plant-air-temperature) -irradiation sensor (measures heat irradation from the greenhouse up to the sky).

Day-climate(8) Afternoonpeak A good start in the morning (at sunrise 17-19°C) Followed by a gradual raise during the morning towards +/- minimum 18-maximum 26°C in the afternoon. We call this a “peak” Reasons of peak: To stimulate evaporation (uptake of water and nutrients),especially when the lightlevels are low. Optimal photosynthesis is at 18-26°C Release of pollen (& activity of bumblebees) When above happens we call this an “active” climate, if not we call it a “death”climate Especially a fast rise in the morning to a peak affects the shape of plant: -fast rise to (high)peak=long internodes,thin stem -slow rise to (low) peak=short internodes, thick stem

Temperature strategy tomato 18-26°C 17-19°C peak 12-17°C 12-17°C PN AN SR SS PN

Day-climate(9) Afternoonpeak -At a low peak there is a higher risk of a “death” climate -The right “peak” temperature depends on: Power of the heads (“slim” or “fat” ) Required heating pipe temperature (see table) Lightintensity (175-250 Watt/m2 important traject) Air Humidity Deficit -Not active HD<3 (“death” climate) -Active HD 3-5 -Very active HD > 5

Rail pipe T, Peak T (heat) & classification Day-climate 18 0-45 death 55 mild 65 active 75 active+ 85 active++ 19 0-40 50 60 70 80-85 20 0-35 45 55 65 75-80 21 0-30 40 70-75 22 0-25 35 65-70 23 30 60-65 24 25 55-60 50-55 26 45-50

4 major “day-climate” items resulting in problems 1.Too much limitation heating pipes 2.Measures to keep lenghtgrowth limited (short internodes) 3.Too late reaction to changes in weather 4.Too fast reduction of minimum pipe temperature

1.Too much limitation heating pipes Maximum pipe temperature-Sunrise heating setpoint MUST be reached. If not, pipe is relative hot when sun gets strong strong rise of temperature higher condensation Botrytis Repeatedly a too low temperature in the morning SHORT INTERNODES FAT HEADS

2.Measures to keep lenghtgrowth limited (shorter internodes) Understandable reasons (height greenhouse, labor, energy) Relative low temperatures around sunrise (night/morning) To drastic means a bad growth fruitsize remains small too!! Especially dangerous in combination with ventilation Always relate ventilation stategy to outside air-temperature Sometimes too much efforts made to keep it cool cold headsbotrytis, fruitskin problems

3.Too late reaction to changes in weather(1) Connect settings on climate computer to outside weather conditions With “standard” equipment: -T-outside -Lightlevel -Wind (speed & direction) -Rain -Outside humidity -Irradiation sensor (measures heat irradiation from the greenhouse up to the sky) cloudy or clear sky?

3.Too late reaction on changes in weather(2) Plant has “history” but no “memory”: -Properties of crop are result of actions in past -Improvement of growth strategy will direct result in improvement of growth, despite bad history “Average” figures: -do not give all required information -more important: what happens at specific moments -graphs give more info

4.Too fast reduction of minimum pipe temperature. 2 main reasons to maintain minimum pipe temperature (rail system) 1.To create evaporation of plant (only at low lightlevels in winter) 2.Mixing cold and warm air: Ventilation at outside T < 15°C cold air “falls” down in the crop This air should be mixed otherwise condensation To create air movement T-pipe should be 15-20°C > greenhouse airtemperature. “Feel” the climate sitting on rail under open window. Reduction of pipe temperature relate to lightlevels and outside air temperature (< 10, 11-15 and >15°C) On most climate computers no automatic connection to outside T!!!!!

Creating air movement in greenhouse Air movement required especially at basis of crop to prevent condensation risks. How? With minimum pipe (T 35-45°C) Tubes under gutter Basic version: -air tube under gutter -tube combined with electric fan -mixing air layers

Tube located under gutter

Outside T < 10 °C Minimum Pipe Strategy (rail) 25 35 45 45 25 -10 (175-250 Watt) PN AN SR Peak SS PN

Outside T 11-15 °C Minimum Pipe Strategy (rail) 25 35 45 40 25 -5 (175-250 W) PN AN SR Peak SS PN

Outside T >15 °C Minimum Pipe Strategy (rail) 20 35 45 40 20 -5 -20 (150-200Watt) PN AN SR Peak SS PN

Dissimilation Use of “sugar” (energy, assimilates) Day & night Day: assimilation+dissimilation Depends on temperature 2 Dissimilation processes: 1.Existing plantcells use energy (f.e. transport) 2.Production of new cells (growth) requires energy

Dissimilation dissimilation Bron: D. Klapwijk

Assimilation minus dissimilation=growth Assimilation (day) > Dissimilation (day & night) Surplus sugar Stronger heads & trusses Bigger tomatoes Higher productionhighest netto fotosynthesis

Netto fotosynthesis Bron: D. Klapwijk dissimilation High netto fotosynthesis Low netto fotosynthesis Bron: D. Klapwijk

Night-climate (1) In night only dissimilation Higher T-night=more (vegetative) growth? Higher night T=more new cells but less “sugars” left for generative parts weak truss smaller tomatoeslower production. Weak trusses at start? High risk of too vegetative plant (unbalanced crop) BIG LEAVES & SMALL TOMATOES Best method to create balanced (generative) crop is to prevent weak trusses. How? GH temperatures must be in balance with: Cropstage (nr. flowering truss, heads/m2) (Natural) light levels

Night-climate (2) Most problems with growth are because of a bad day-climate Don’t “repair” a bad growth because a bad “day climate” by raising the night T First optimize day-climate General thought: (More) equal temperature regime=more growth??? (lower day T-higher night T) There are some some exceptions to this “rule”:

Night-climate (3) Equal Temperature D/N=Vegetative? Also observed in practice: At (extreme) cold nights a high night T  high pipe T  less humidity  leafs get smaller. A lower GH-T during day can also result in a “death” climate  plant does not evaporate no transport of water, nutrients and assimilates =no growth at all!!!

24-hr average T-regulation 1 Balance between crop parameters, light and lightlevels In young crops relative high night-T to create leafs as fast as possible. Truss must stay strong!!! At low light-levels and bigger plant lower 24-hr.averages mainly by adjusting night-temperature.

24-hr average T-regulation 2 Most important factors involved Plantsize (nr. flowering truss) Bigger plants have higher dissimilation losses lower night-temperatures Daily lightsum At lower lightlevels lower assimilation prevent dissimilation > assimilation by lower night-temperatures Stem-density (and distribution) At higher stemdensity less light per headless assimilation  prevent dissimilation>assimilation by lower night-temperatures Pepino-virus Consider the virus as a parasite that takes assimilates lower night-temperatures to reduce dissimilation losses. Observation truss When truss is too weak lower night-temperature. When truss is too strong raise day-temperature Other factors(greenhouse, lighttransmission etc.)

24-hr average T-regulation 3, table T-heating pipes important factor!!!!!!!!!!!!!! 24-Hr Temperature regulation related to plant-size and daily lightsum Truss* 100 200 300 400 500 1000 Joule/cm2/day 1 17,3 17,5 17,8 18,2 18,5 20,1 °C 24-Hr 2 17,0 17,6 17,9 19,9 3 16,8 17,7 18,0 19,6 4 16,5 17,1 17,4 19,4 5 16,3 17,2 19,1 6 16,0 16,6 16,9 18,9 7 15,8 16,7 18,6 8 15,5 16,1 16,4 18,4 *Flowering Truss

24-hr average T-regulation 4 24-Hr Temperature regulation related to plant-size and daily lightsum. A good guideline, but every situation is different. Keep watching the plant, especially head+truss Too low 24 Hr-temperatures may create too strong trusses and too coarse flowers. Mainly a danger in young crops with low fruitload.(Truss 1-5 flowering). Raise 24 Hr by: 1.First optimize day-temperature (higher) 2.Crop must be heated at sunrise (f.e 171819°C) 3.Higher night by shorter PN and longer AN

24-hr average T-regulation 5 Weak truss? Step 1.Lower T-night (pre-night) Step 2. (less common) Lower T-day (but avoid “death” climate pollen must release) Too strong truss? Step 1.Higher T-day (also T at sunrise) Step 2. (less common) Higher T-night (shorter pre-night)

24-hr average T-regulation 6 Pre-Night & After-Night (PN, AN) Night-temperature used to correct 24 Hr.T Reason PN and AN mainly technical: -PN: cool down with cold pipe and screen open (closed if very cold) -AN: warm up with hot pipe and closed screen In PN pipe is cold , relative humidity gets (too) high. As long GH temperature goes down there will no be condensation (maximum length PN!!) Rough practical guideline: maximum 4-6 hours with “cold” pipes=maximum lenght pre-night (2 hours before- 4 hours after sunset After stabilisation temperature, greenhouse must be heated up with maximum 1°C per hour (faster=higher risk of condensation)

Speed of growth “Speed” Flower-Harvest approximately 6-10 weeks Lightlevel/plantload determines 24 Hr-average. 24 Hr-average determines speed. Important for speed is optimal day-climateCold heads and a death climate cannot be compensated by a warmer night Higher 24 Hr-averages with relative warm nights will result in: 1.slightly faster from flower to harvest (less then a week) 2.Higher risk of weak heads and trusses (quality problems in hot summers) 3.Smaller fruits (but kg’s not compensated by more trusses and fruits) 4.Higher risk of unbalanced growth (too vegetative) because of weak trusses & small fruits

light conditions Green scheduler crop planning model Conclusion A good growth is mainly a matter of day-climate management. Best results (quality and production) are obtained at growers who: -have excellent feeling for crop and day-climate -know how to translate this feeling to settings on computer -have crop heated up sufficient at sunrise -have a relative cool night-temperature -look more at the crop instead of the figurs/numbers -react keen on changing outside weather conditions -have a crop planning that is in balance with (natural) light conditions Green scheduler crop planning model

Questions?

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