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PRINCIPLES OF CROP GROWTH SIMULATION MODELLING
Potential production
The Rice System and boundaries – Potential Production Situation
Radiation, CO2, O2
Temperature
A. GROWTH
Photosynthesis (CO2 assimilation)
CO2 + H2O + solar energy => CH2O + O2
Respiration (maintenance, growth)
CH2O + O2 => CO2 + H2O + chemical energy
Assimilation respiration = net growth rate
B. DEVELOPMENT
Development rate = f(temperature)=> growth period=> partitioning
C. BIOMASS PRODUCTION = growth rate x growth period
PROCESSES OF CROP GROWTH
A. CROP GROWTH RATE
Daily gross crop assimilation rate (kg CH2O ha1 d1)
CO2 assimilation
I. CO2 assimilation of a single leaf
• Individual leaf light response curve
II. Canopy CO2 assimilation
• Integration over leaves in canopy (depth, z)• Integration over leaves in time (day, t)
III. Leaf area growth in time
I. CO2 assimilation of a single leaf
Cross section of a leaf through a stoma (a), indicating components of resistances to CO2 diffusion (b).
radiation(Wm-2)per mm
PAR
50%
1.0
.5
500 1000 1500ultra violet visible infra-red wavelength (nm)
Spectral composition of global radiation, discriminating between direct radiation (clear area) and diffuse (i.e. indirect) radiation scattered by clouds (hatched area). PAR = photosynthetically active radiation.(Source: Monteith and Unsworth, 1990. Principles of environmental physics. Edward Arnold, London, 291 p.)
Schematic representation of a leaf chamber for the measurement of CO2 assimilation.
80
60
40
20
00 100 200 300 400
Fg C3
Fg C4
APAR (J/m2/s)
Fm C3 crop
Fm C4 crop
Fg (kg CO2/ha leaf/hr)
Leaf light response curve:
Fg = gross rate of CO2 assimilationFm = maximum rate of CO2 assim. at high light intensity = initial light use efficiencyAPAR = Absorbed Photosynthetic Active Radiation
Fg = Fm (1e(APAR / Fm))
C3 crops C4 crops
Potato, sugar beet, wheat, rye, barley, rice, rape, soy bean, broad beans, almost all trees
Sorghum, maize, millet, sugarcane, rhodes grass, sisal, mangrove
Characteristic values of Fm and
Fm
C3 crops 40 (15 - 50) 0.45
C4 crops 70 (30 - 90) 0.45
Fm : kg CO2 ha leaf1 d1
: (kg CO2 ha leaf1 h1)(J m2 s1)1
0 200 400 600 0 200 400 600 0 20 3010 40 50
0
25
50
75
100
0 0
25
50
75
100
1
2
0
25
50
75
100
0
1
2
0
1
2
net assimilation rate net assimilation rate net assimilation rate
[kg (CO2) ha-1 h-1] [mg (CO2) m-2 s-1] [kg (CO2) ha-1 h-1] [mg (CO2) m-2 s-1] [kg (CO2) ha-1 h-1] [mg (CO2) m-2 s-1]
C3C4
C3C4
C3C4
A B C
PAR [J m-2 s-1] internal CO2 [ppm] temperature [oC]
The effect of light (a) CO2 concentration (b) and temperature (c) on net assimilation rate of a C3 (solid line) and a C4 (dashed line) species. Assimilation rates in (b) and (c) refer to light saturated values. In (b) CO2 concentration in the stomatal cavity is used to avoid confounding stomatal to changes in external CO2 concentration.
Effect of N in leaf on photosynthesis
Van Keulen and Seligman, 1987
II. Canopy CO2 assimilation
Direct light
Diffuse light
Canopy reflection (5%)
Atmospheric scattering
Weather station: radiometerIncident radiation
diffuse radiation
direct radiation
II.1 Integration over leaves in canopy (depth, z)
Light and single leaf
Light and multiple leaves
0
5
10
15
20
25
30
35
40
45
50
55
60
0.0 0.2 0.4 0.6 0.0 0.2 0.4 0.6 0.8 1.0
depth [cm]
A
LAI rel. light intensity
The distribution of leaf area over the depth (I.e. LAI per layer of 5 cm) and of the light intensity in the crop, relative to the light intensity above the (sugar beet) crop (a). The relation between relative light intensity and cumulative LAI calculated from the top downwards (b). LAI = leaf are index [in m2 (leaf surface) m-2 (ground surface)].
Extinction of radiation in the canopy
PARd = PAR0 e( LAId)
PARd = PAR at depth d in canopy
PAR0 = PAR above crop canopy
LAId = Leaf Area Index above d
= extinction coeff. (0.5 - 0.7)
Canopy (leaves) architecture
II.2 Integration over leaves in time (day, t)
Time course of PAR and crop CO2 assimilation rate on an average (left) and a clear and overcast day (right) in June in the Netherlands.
0
100
200
300
400
PAR
[J m-2 s-1]
Agross
[kg (CO2) ha-1 h-1]
0
100
200
300
400
0
20
40
60
80
0
20
40
60
80
2 6 10 14 18 22 2 6 10 14 18 22
time [h] time [h]
AgrossPAR
Average dayClear day
Overcast day
Summary calculation of daily canopy gross CO2 assimilation rate:
• At any depth in the canopy, at any time of the day (and latitude, season), calculate gross leaf CO2 assimilation rate from ‘leaf light response curve’ and PARd.
• Integrate over depth (LAId) of the canopy
• Integrate over day length (time of day)
Canopy assimilation = t z (leaf assimilation)
So far, gross CO2 assimilation rate was expressed in kg CO2 ha1 d1
Since:
CO2 + H2O + solar energy => CH2O + O2
Molecular weight of CO2 is 30
Molecular weight of CH2O is 44
To calculate daily gross accumulation rate of assimilates:
1 kg CO2 ha1 d1 CO2 assimilation rate
= 30/44 kg CH2O ha1 d1
Month f Aclear Aovercast Aaverage Agross
J 0.47 616 252 445 303
F 0.34 674 281 540 368
M 0.37 734 311 577 394
A 0.28 781 334 656 447
M 0.42 800 342 608 414
J 0.52 804 342 564 384
J 0.59 803 343 532 362
A 0.62 791 339 511 348
S 0.58 757 323 505 345
O 0.54 698 293 479 327
N 0.54 633 261 432 295
D 0.54 600 244 408 278
------ kg CO2 ha1 d1 ------ kg CH2O ha1 d1
Rice canopy assimilation rate, Los Baños, Philippines
III. Leaf area growth in time
0
1
2
3
4
5
6
7
0 10 20 30 40 50 60 70 80 90 100 110 120
TIME
Exponentialphase
Linear phase
Leaf death
Seedbed
Leaf Area Index (ha leaf ha-1 soil)
Exponential phase: leaf area growth determined by temperature
LAIt = LAI0 e(RGRL Tsum)
RGRL = Relative Growth Rate Leaves (°Cd)-1
Tsum = Temperature sum since emergence (°Cd)
Linear phase: leaf area growth determined by assimilates available, as expressed in weight of leaves
LAIt = SLA Wlvg,t
SLA = Specific Leaf Area (ha leaf kg-1 leaf)
Wlvg = Weight of green leaves (kg ha-1 soil surface)
NET CROP GROWTH RATE
Crop respiration
10
14
18
22
0.2
0.4
0.6
0.8
1.0
16 20 24 4 8 12 16 20 24 4 8 12 16
Growth respiration
Maintenance respiration
26 April 27 April 28 April
Figure 2.24 CO2 efflux of an enclosed sward of perenial ryegrass, at ambient temperature during two days of darkness.
(a) ______ : continuous record of CO2 efflux; --------- : maintenance respiration, calculated as the mean rate of CO2 efflux after 40-46 hours of darkness, adjusted for the effect of temperature.
(b) continuous record of air temperature in closure.
Source : Jones, Leafe, Sites & Collett, 1978. Ann. Bot. (42):693-703.
Maintenance respiration
• Resynthesis components (enzyme turnover: 10% d1)• Concentration gradients• Metabolic activity
Maintenance respiration rate: Rm = f(composition, weight)
Rm = 0.02 Wleaf + 0.015 Wstem + 0.01 Wroot + 0.03 Wstorage
(in kg CH2O (kg CH2O)1 d1 )
Rm,t = Rm Q10 [ (T Tref) /10 ]
with Q10 = 2, and Tref = 25 ºC
and at any temperature:
For lowland rice (IR72):
Growth respiration
Sugars ( CH2O) => structural matter
Conversion efficiency:
Eg = f(chemical composition)
in (kg dry matter) (kg CH2O)1
• Uptake nitrogen and minerals
• Transport of sugars
• Synthesis end-product
Carbohydrates 0.826
N-compound from NO3 0.404
N-compound from NH+4 0.616
Organic acids 1.104
Lignin 0.465
Lipids (fats) 0.330
Conversion efficiency for chemical compounds
Growth respiration
Composition (%) and conversion efficiency for rice:
Leaf Stem Root Panicle
Carboh. 52 62 56 76
Protein 25 10 10 12
Fats 5 2 20 2
Lignin 5 20 20 6
Org. ac 5 2 2 2
Mineral 8 4 10 2
Eg 0.75 0.75 0.75 0.68
Net crop growth rate
Daily rate of increase in structural dry weight of a crop (dW):
dW = Eg (Agross Rm W) in: kg dry matter ha1 d1
where:• Eg = conversion efficiency (kg dry matter (kg CH2O)1)
• Agross = gross CO2 assimilation rate (kg CH2O ha1 d1)
• Rm = maintenance respiration (kg CH2O) (kg CH2O)1 d1
• W = dry weight of the crop (kg ha1)
Net crop growth rate
Mean values of Rm and Eg, at 20 °C
Rm Eg
Root/tuber crops 0.010 0.75
Cereals (rice) 0.015 0.70
Protein-rich seed crop 0.025 0.65
Oil-rich seed crop 0.030 0.50
For rice in Los Baños, Philippines
dW = Eg (Agross Rm W)
Dry season – April:
dW = 0.70 (447 0.015 5000) = 261 (kg dry matter) ha1 d1
Wet season – October:
dW = 0.70 (327 0.015 5000) = 176 (kg dry matter) ha1 d1
0
5000
10000
15000
20000
25000
0 50 100 150 200 250 300 350
266 kg DM ha-1 d-1
177 kg DM ha-1 d-1
Dry season
Wet season
kg DM
Day of year
Rice IR72, IRRI farm 1991-1993, Los Baños
Month f Aclear Aovercast Aaverage Agros Anet
J 0.47 333 120 233 159 59
F 0.34 445 169 351 239 115
M 0.37 586 233 455 310 165
A 0.28 737 304 616 420 241
M 0.42 843 354 638 435 252
J 0.52 892 377 624 426 245
J 0.59 873 368 575 392 222
A 0.62 788 329 503 343 188
S 0.58 652 264 427 291 151
O 0.54 497 193 333 227 106
N 0.54 364 133 239 163 62
D 0.54 304 107 198 135 42
------ kg CO2 ha1 d1 ------- kg CH2O ha1 d1
Rice canopy assimilation rate, Beijing, China
Rice, Changle (Beijing), 2001, China
0
5000
10000
15000
20000
25000
0 50 100 150 200 250 300 350
232 kg DM ha-1 d-1
kg DM
JD305
HD502
HD297
Day of year
B. CROP DEVELOPMENT
Development rate and assimilate partitioning
Thermal Unit (or temperature sum):
anthesis maturity
(T - T0) dt and (T - T0) dt
emergence anthesis
Expressed in day degrees (°C d)
where T = average daily temperature
T0 = base temperature (0 - 10 °C)
Per crop (and cultivar), there is constant TU between emergence-anthesis, and anthesis-maturity
Rice variety IR72
0
500
1000
1500
2000
2500
0 0.5 1 1.5 2
Development stage
Temperature sum (°C)
Flowering Maturity
Development rate is inverse of number of degree days between development stages (°Cd 1)
Period DVS IR72 HD502
Juvenile 0.0-0.4 0.001161 0.000506
Photoperiod-sensitive
0.4-0.65 0.000064 0.000758
Panicle formation
0.65-1.0 0.001152 0.000769
Grain filling 1.0-2.0 0.000504 0.001417
Partitioning of assimilates
Assimilate partitioning is function of development stage (DVS) of crop.
Example for fraction of assimilates (growth) partitioned to the shoot (FSH), for rice:
DVS FSH
0.00 0.50
0.43 0.75
1.00 1.00
2.00 1.00
E.g. at development stage of 0.43 => 75% of daily growth goes to the shoot, and 25% to the roots.
Partitioning of assimilates; Rice IR72
Fraction daily dry matter increase
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.5 1 1.5 2
SHOOT
ROOT
Development stage
ROOT
SHOOT
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.5 1 1.5 2
STORAGE ORGAN
STEM
LEAF
Development stage
Fraction daily dry matter increase
Partitioning of assimilates; Rice IR72
C. BIOMASS PRODUCTION
Total crop growth simulation
Photosynthesis
Assimilatepool Biomass
Leaves
Stems
Panicles
Roots
LAI
Developmentstage
Maintenancerespiration
Growthrespiration
Partitioning
Developmentrate
N leaves
Light
Temperature
Crop model Potential Production
Reduced grain yield through spikelet sterility; effect of temperature
Horie (1993)
Input
1. Weather data: daily temperature, radiation => Weather data file
2. Management: emergence date, density, etc => Experiment data file
3. Crop characteristics: Fm, partitioning, etc => Crop data file
Output
• Time course of leaf area index, biomass
of various crop organs
• Yield, yield components
0
1
2
3
4
5
6
7
0 10 20 30 40 50 60 70 80 90 100 110 120
TIME
Run 3, LAIRun 3, LAI_OBS
IR72; Los Baños; DS 1992; 225 kg N ha1
LAI simulated
LAI measured
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
0 10 20 30 40 50 60 70 80 90 100 110 120
TIME
Run 3, WAGTRun 3, WAGT_OBSRun 3, WLVGRun 3, WLVG_OBSRun 3, WSORun 3, WSO_OBS
Total biomass
Panicle biomass
Green leaf biomass
kg dry matter ha-1.