Improvement of water use efficiency and yield of greenhouse tomato ...

Improvement of water use efficiency and
yield of greenhouse tomato using tension
measurements
Caron 1,2 , J, Lemay 1 , I , Dorais 3 , and M, Pépin 1 , S,
1
Soil Science and Agrifood Engineering Department, Laval University,
1
Hortau, 3 Plant Science Department, Laval University and Agriculture
and Agrifood Canada

Literature
• Tomatoes grown on suspended gutters, using
rockwool slabs and coir as growing media and
drippers to irrigate
• Irrigation controlled
using timers + irradiance
levels

Introduction
• Greenhouse tomato grown over years in rockwool
and now coir -Expensive to buy
-No reuse possible in North
America : high land-filling
costs (rockwool)
Growers asked for new
substrates to be developed
Organic and sustainable

Literature
• Tomatoes grown on suspended gutters, using
containers and drippers

Literature
• Sawdust and bark are very attractive: still cheap and
abundant
• A lot of research on substrates, particularly sawdust
and bark
• New research is needed:
• Industrial processes evolve and hence the by-products
• Basic concepts on substrates physics have evolved
• Important for growers to have a wide variety of highly
performing substrates

Literature
• Changing substrates means adapting irrigation
as greenhouse tomato highly sensitive to water
stress (Salter, 1954; Waister et Hudson, 1970)
• Recent results, particularly sawdust/peat
‣ Juneau (2004): Fall crop
Yields in sawdust-peat mix < rockwool : improved with
better irrigation control
‣ Allaire et al. (2005): yields related to water retention and aeration

Plant growth or photosynthesis (Caron, Xu and
Bernier, 1995 and 1998)
100
80
Irrigation set point
Type 2 rockwool
60
40
A
Hydric
comfort
B
C
Type 3 (sawdust peat)
20
Stress initiation
0
Oxygen deficiency
Tension (cbars )
0.8 30
Relationship between plant performance and tension
Container
dry

Literature: tension set points
• Extensive work on tension set points in mineral
soils
• Extensive work in peat substrates for
greenhouse tomato and ornamentals
• 5-10 cbars
• Little work done on appropriate set points for
greenhouse tomato in sawdust/peat mix
• Need to identify critical irrigation set points
with the proposed new mix for greenhouse
tomato

Tools to monitor irrigation
• Frequent irrigation: up to 40 times a day
Need to use fast response tension sensors
• Need to estimate tension at different
locations within a greenhouse
(Hydrozoning)

Cyr, 1990, M.Sc. thesis
Detection of zone of stress when using tensiometers
% of surface in partial drought
80
70
60
50
40
30
20
10
0
0 1 2 3 4 5
Number of tensiometers in a 200 sq m greenhouse

Need to collect real time tension data from many
locations
Wireless fast response tensiometers can help to
adequately estimate average tension within an
irrigation zone

Such systems exist for field and greenhouse
applications

Objectives
‣ Define appropriate tension set points for
sawdust/peat mix to get the highest yields and
the best water use efficiency

1 step: identify a first set point from plant activity
1. Well watered plant
2. Remove drippers and let the plant dry out the
substrate
3. Take measurements of stress indicators:
‣ xylem water potential,
‣ transpiration,
‣ photosynthesis
‣ Stomatal conductance
4. Plot the relationships to identify threshold

1 step: identify a first set point from plant activity
Commercial grower:
Took measurements throughout a whole year :4
different times (Dec, Jan, April , July)
University
Took measurements of stress indicators in April and
July
Plot the relationships to identify threshold

1 step: identify a first set point from plant activity
Maximum photosynthesis (micromole CO2/m2 s)
30
25
20
15
10
5
Timers
Sawdust/peat grower
Rockwool grower
Rockwool University
Peat/sawdust University
0
0
2
4
6
Tension (cbars)
8
10

2 step: test the setpoints in growth experiments
• Laval University, Québec, Canada and a
commercial grower (7 complexes in Canada)
• Growth period January to August 2005
• Cultivar ‘Trust’
• Randomized block design (6 replicates)
• Sawdust-peat mix (2:1 vol vol) average particle
size 0.5-1mm
• Venlow greenhouse

Material and methods
Treatments
RW Rockwool, timer irrigation + adjustment
based on irradiance
N Sawdust/peat mix, timer irrigation +
adjustment based on irradiance
T
Sawdust/peat mix, irrigated using wireless
fast response tensiometers, controlled by
computer (1.2 cbars day/ 2.0 cbars at night)

Results and discussion
Fig. 1 Yield of greenhouse tomato with different substrates
and irrigation treatments
Yield (kg/plant)
12
11.5
11
10.5
10
Total yield
Marketable yield
1 kg/plant (2.5
pounds)
9.5
Rockwool Sawdust/peat + timer Sawdust/peat+
Irrigation treatments tensiometer

Results and discussion
Fig. 2 Amount of water used different substrates and
irrigation treatments
3500
Amount of water (ml)
3000
2500
2000
1500
1000
500
Rockwool
Sawdust/peat + timer
54 %
Sawdust/peat+tensiometer
67 %
0
Applied Leached Used by plant
Irrigation treatments

Results and discussion
Table 1. Total biomass and percent dry matter in fruit
Dry matter (kg) % dry matter
Treatments Stem Leaves Fruits Marketable Total
RW 0.07 0.22 0.60 4.83 5.03
N 0.07 0.23 0.63 4.75 4.88
T 0.08 0.24 0.66 4.82 5.05
P value for treatment effect 0.007 0.03 0.07 0.73 0.44
Contrast
RW vs T 0.002 0.003 0.006 0.94 0.87
N vs T 0.011 0.090 0.147 0.53 0.16

Results and discussion
‣ No change in fruit quality (lycopen,
antioxydant, dry matter, soluble sugars,
acidity)
‣ 50% decrease in substrate costs
‣ More sustainable growing medium
‣ Reduced costs as no land filling

Conclusions
‣ Appropriate set points for sawdust/peat mix
now derived
‣ 10% yield increase with change in substrate
and use of tensiometer
‣ 50% decrease in substrate costs
‣ Higher water use efficiency (67% with T vs
54% with N)
‣ No change in fruit quality (lycopen,
antioxydant, dry matter, soluble sugars,
acidity)

Thank you for your attention!
Thanks to
Natural Science and Engineering Research Council of Canada
Jocelyne Moreau, Linda Gaudreau (Savoura)
Sébastien Descôteaux (Hortau)
Johanne Tardif (Maibec)

Tensiometers
•Direct measurement of plant stress
•Well accepted concept (1930)
•A lot of well known threshold
values to initiate irrigation