Prediction of Field Germination
Using a
Wet Thermal Accumulation Model
Jennifer Coleman, Bruce Roundy and Brad Jessop
Brigham Young University
Department of Plant and Animal Science
Provo, Utah
Disturbance
Germination
Forbs
Appar blue flax
Eagle yarrow
Grasses
Hycrest crested
wheatgrass
Anatone
Bluebunch
wheatgrass
Bottlebrush
squirreltail
Cheatgrass
Wet Thermal Accumulation
¾ Germination requirements
1) Water
¾ Above base water potential (MPa)
2) Temperature
¾ Above base temperature for some time (degree days)
Wet Degree Days
¾Crested wheatgrass requires 62.9 wet degree days for 50%
germination
¾Base water potential: -1.5 MPa
¾Base temperature: 0° C
¾Time to germination:
¾62.9 days at 1° C
¾0.0417 degree days/1hour at 1°C
¾6.3 days at 10 ° C
¾0.417 degree days/1hour at 10°C
¾3.5 days at 20° C
¾0.833 degree days/1hour at 3° C
Methods
1. Constant temperature germination trials
2. Seed bag burial and retrievals
3. Small plot seeding
•
•
Density
Survival
Germination Trials
• Constant Temperatures:
– 5,10,15,20,25,30,35 °C
• What we measured:
– Days to 25% germination
– Days to 50% germination
• What we needed to know:
– Hourly germination rate
Germination Rate
Crested wheatgrass
0.35
3 days
●
1/Days to Germination
0.3
0.25
●
4.8 days
0.2
0.15
0.1
7.5 days
●
● 12.5 days
0.05
0
0
5
10
15
20
25
30
Temperature (C)
days to 25% germ ination
days to 50% germ ination
35
40
Germination Rate
Appar Blue flax
0.4
1 /D a y s to G e r m ina tion
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
0
5
10
15
20
25
30
Temperature (C)
1/days to 25% germ ination
1/days to 50% germ ination
35
40
Thermal accumulation:
2 methods
Cold
Warm
Seeds begin
to germinate
1) Thermal
Thermal
accumulation
accumulation
stops
resumes
2) Thermal
accumulation
begins again
Germination
stops
Ungerminated
Germination
Dry
Wet
Skull Valley
Lookout Pass
Seedbed Monitoring
• Temperature
– Depths:
• 2-3 cm
• 15-16 cm
• 28-30 cm
• Moisture
– Depths:
• 2-3 cm
• 15-16 cm
• 28-30 cm
Study Sites
Block Year
1
Small Plots
Seedbags
BlockSmall
1 Plots
2
Seedbags
2
Small Plots
Seedbags
BlockSmall
2 Plots
2
Seedbags
3
Small Plots
Seedbags
BlockSmall
3 Plots
2
Seedbags
4
Small Plots
Seedbags
BlockSmall
4 Plots
2
Seedbags
1
Skull Valley
1
1
1
Lookout Pass
Seedbags
Fall 2005-Spring 2006
Planted:
3
2/27/2006
3/16/2006
4
2/27/2006
3/28/2006
5
2/27/2006
4/11/2006
3/16
6
2/27/2006
4/25/2006
3/28
7
2/27/2006
5/10/2006
Retrieved:
12/6/05
9 seedbag
1/19/06
retrievals
10/15/05
2/27/06
4/11
4/25
5/10 & 5/11
3/28/06
4/11/06
4/11/06
4/11/06
Seedbag germination:
Skull Valley
1
Germination (%)
0.8
0.6
Y arrow
Crested
Cheatgrass
Squirreltail
Blue f lax
Bluebunch
0.4
0.2
0
2/27-3/16
2/27-3/28
3/28-4/11
2/27-4/11
4/11-4/25
Date Plante d - Date Re trie ve d
2/27-4/25
2/27-5/8
Seedbag germination:
Lookout Pass
1
Germination (%)
0.8
0.6
Y arrow
Crested
Cheatgrass
Squirreltail
Blue f lax
Bluebunch
0.4
0.2
0
2/27-3/16
2/27-3/28
3/28-4/11
2/27-4/11
4/11-4/25
Date Plante d - Date Re trie ve d
2/27-4/25
2/27-5/10
Seedbag Retrievals
1) Thermal accumulation starting over at
individual wet periods
• >25% germination?
• >50% germination?
2) Continuous thermal accumulation during
all wet periods
• >25% germination?
• >50% germination?
# accurate predictions/total seedbag predictions
Wet Thermal Accumulation Model
Accuracy: Lookout Pass
18
16
14
12
10
89%
100%
100%
89%
94%
8
6
4
2
17%
0
yarrow
Crested
wheatgrass
cheatgrass
individual wet periods
Bottlebrush
squirreltail
∑wet periods
blue flax
Bluebunch
wheatgrass
Wet Thermal Accumulation Model
# accurate predictions/total seedbag predictions
Accuracy: Skull Valley
18
16
14
12
89%
10
8
100%
100%
72%
72%
89%
94%
72%
6
4
2
22%
17%
0
yarrow
Crested
wheatgrass
cheatgrass
Bottlebrush
squirreltail
individual wet periods
blue flax
∑wet periods
Bluebunch
wheatgrass
Wet Thermal Accumulation Model
# accurate predictions/total seedbag predictions
Accuracy: Skull Valley
18
16
14
12
89%
10
8
100%
100%
72%
72%
89%
94%
72%
6
4
2
22%
17%
0
yarrow
Crested
wheatgrass
cheatgrass
Bottlebrush
squirreltail
individual wet periods
blue flax
∑wet periods
Bluebunch
wheatgrass
Seedbag Retrieval 4
2/27-3/28/06
0
0.2
15
0.4
10
0.6
0.8
5
0
27-Feb
1
1.2
2-Mar
6-Mar
10-Mar
14-Mar
18-Mar
-5
Temperature
Soil Moisture
22-Mar
26-Mar
1.4
Soil Moisture (-MPa)
Soil Temperature (C)
20
Wet Thermal Accumulation Model
# accurate predictions/total seedbag predictions
Accuracy: Skull Valley
18
16
14
12
83%
10
89%
100%
100%
89%
78%
8
94%
78%
6
4
2
22%
17%
0
yarrow
Crested
wheatgrass
cheatgrass
Bottlebrush
squirreltail
individual wet periods
blue flax
∑wet periods
Bluebunch
wheatgrass
Seedbed Conditions:
Lookout Pass
0
23
0.2
0.4
0.6
13
0.8
8
1
1.2
3
1.4
-2
2/27
3/6
3/14
Temperature
Moisture
3/22
Soil Moisture (-MPa)
Soil Temperature (C)
18
Small Plots
Block Year
1
1
2
1
2
2
1
3
2
1
4
2
Small Plots
Seedbags
Small Plots
Seedbags
Small Plots
Seedbags
Small Plots
Seedbags
Small Plots
Seedbags
Small Plots
Seedbags
Small Plots
Seedbags
Small Plots
Seedbags
Treatments
Crested wheatgrass
60
8
7
cover
Cover (%)
a
30
20
A
density
b
a
a
ab
ab
3
b
ab
10
5
4
ab
ab
a
2
b
1
0
0
PCH
FCH
UD
Lookout Pass
PCH
Tre atme nt
FCH
Skull Valley
UD
2
40
6
Density (m )
50
Seedling Density and Survival 2006
Lookout Pass
204
115
100
Crested
Cheatgrass
Squirreltail
Bluebunch
Blue flax
Yarrow
90
80
# seedlings/m
70
60
50
40
30
20
10
0
3/24
4/13
5/3
5/23
6/12
7/2
7/22
8/11
8/31
Seedling Density and Survival 2006
Skull Valley
100
Crested
Cheatgrass
Squirreltail
Bluebunch
Blue flax
Yarrow
90
80
# seedlings/m
70
60
50
40
30
20
10
0
3/24
4/13
5/3
5/23
6/12
7/2
7/22
8/11
8/31
Seedling Mortality
Seedling Mortaility (%)
100
75
98%
99% 99%
96%
93.5%
50
85%
68%
65%
a
55%
80%
69%
79%
25
0
Yarrow
Crested
Cheatgrass
Lookout Pass
Squirreltail
Skull Valley
Blue flax
Bluebunch
Seedbag Conditions
40
35
Temperature (C)
30
25
20
15
10
5
0
3/23
4/16
5/10
6/3
Skull Valley temp
6/27
Lookout Pass temp
7/21
8/14
40
0
35
0.2
30
0.4
25
0.6
20
0.8
15
1
10
1.2
5
1.4
0
1.6
3/23
4/16
5/10
6/3
SV moisture
6/27
LP moisture
7/21
8/14
Soil Moisture (-MPa)
Seedbag Conditions
Conclusions
• Can a wet thermal accumulation model be
used to predict germination?
– Yes, if no special requirements are needed for
germination
• Ex: light for yarrow
• Precautions:
– Cold conditions
– High temperature and moisture fluctuations
Further Research
• Fall 2006 and Spring 2007 seedbag
retrievals
• Spring and Summer 2007 small plot
readings
• Modelling emergence and survival: Root
growth
Questions?