1. Radiation Use Efficiency in Cotton: Effect of Environment and Plant Growth Regulators
Evangelos Gonias, Derrick Oosterhuis,
Androniki Bibi and Bruce Roberts
University of Arkansas
Department of Crop, Soil and Environmental Sciences

2. Introduction Crop growth depends on:
Amount of intercepted radiation
Time allowed for growth
Fraction of intercepted radiation (f) calculated by the Beer’s law:
f = I/I0 = e-k·LAI
Cotton canopy extinction coefficient (k):
(Sinclair and Muchow, 1999)
(Monsi and Saeki, 1953)
(Constable, 1986; Rosenthal and Gerik, 1991; Sadras and Wilson, 1997)

3. Radiation Use Efficiency (RUE)
Effectiveness of a crop to convert intercepted radiation to dry matter.
Amount of dry matter produced per unit of radiation intercepted (g·MJ-1).
Correlation described as linear.
Cotton RUE: 1.31 to 1.92 g·MJ-1 of intercepted PAR.
(Monteith, 1977)
(Rosenthal and Gerik, 1991; Pinter at al., 1994; Sadras and Wilson, 1997)

4. Factors affecting RUE Biotic stress: Abiotic stress:
Spider mites reduced cotton growth without reduction in light interception.
Abiotic stress:
Salinity reduced RUE of soybean by 40%.
Water deficit reduced RUE by 54% and 64% for two peanut cultivars.
Increasing vapor pressure deficit decreased RUE.
(Sadras and Wilson, 1997)
(Wang et al., 2001)
(Collino et al., 2001)
(Stöckle and Kiniry, 1990)

5. Vapor pressure deficit (VPD)
VPD>1 kPa decrease leaf photosynthesis in wheat.
Increasing VPD decreased RUE by a slope of:
0.65 and 0.85 g·MJ-1·kPa-1 for sorghum and corn.
1.48 g·MJ-1·kPa-1 for potato.
0.53 g·MJ-1·kPa-1 for barley and wheat (solar).
(Leach, 1979)
(Stöckle and Kiniry, 1990)
(Manrique et al., 1991)
(Kemanian et al., 2004)

6. Effect of VPD on RUE
RUE at high VPD expressed as percentage of RUE at the lower VPD.
(Summarized by Kiniry et al., 1998)
Crop
Low VPD
High VPD
RUE
References
- kPa -
- % -
Maize 1
2.5 75
Bunce, 1982
0.8
2.0 84
Morison and Giford, 1993
0.4
1.9 93
Dai et al., 1992
2.7 79 “
3.5 64
1.25
4.0 48
El-Sharkawy et al., 1985
Sorghum 74

7. Studies Effect of environment on radiation use efficiency of cotton.
Effect of plant growth regulators on radiation use efficiency of cotton.

8. Measurements
Data recorded between pinhead square stage (PHS) and three weeks after flowering (FF+3).
Measurements:
Light interception (weekly)
Dry matter (every days)
Weather data:
Temperature
Relative humidity
Photosynthetically active radiation

9. Effect of environment Hypothesis: Objective:
Radiation use efficiency of cotton differs among geographic locations due to differences in environmental parameters (i.e. vapor pressure deficit).
Objective:
Determine and compare the radiation use efficiency of cotton in Arkansas and California.

10. Materials and Methods Locations: Years: 2006 and 2007
Marianna, AR (Cotton Branch Station, UA)
Fresno, CA (Dr Bruce Roberts, CSU)
Years: 2006 and 2007
Cultivar: DP444BR
Populations:
5 plants / m2
10 plants / m2
5 replications

11. RESULTS

12. Weather Data 2006
Average values between pinhead square stage and three weeks after flowering.
Location
VPD
Tmax
Tmin RH
PAR
kPa Cº %
MJ·m-2
Marianna, AR
1.68
33.1
21.3
67.5
10.12
Fresno, CA
2.92
37.7
19.3
43.7
13.30
P-value
<0.001
0.002

13. Weather Data 2007
Average values between pinhead square stage and three weeks after flowering.
Location
VPD
Tmax
Tmin RH
PAR
kPa Cº %
MJ·m-2
Marianna, AR
1.35
32.5
21.3
75.5
8.75
Fresno, CA
2.49
34.2
15.9
44.9
12.91
P-value
0.020
<0.001

14. Vapor Pressure Deficit
Daily vapor pressure deficit for Marianna, AR and Fresno, CA between pinhead square stage and three weeks after flowering.
2006
2007

15. Radiation Use Efficiency
Across Years
No significant YearRUE interaction (P=0.9246)

16. Effect of Plant Growth Regulators
Hypothesis:
Plant growth regulators affect crop growth and canopy dynamics and therefore alter radiation use efficiency of cotton.
Objective:
Determine the effect of plant growth regulators on radiation use efficiency of cotton.

17. Materials and Methods
Location: Fayetteville, AR (University of Arkansas Agricultural Research and Extension Center)
Years: 2006 and 2007
Cultivar: DP444BR
Populations: 10 plants / m2
5 replications in a RCB design
Treatments (applied at PHS, PHS+10 days and FF):
Untreated control
Mepiquat chloride at 8 oz/acre

18. Mepiquat Chloride 1,1-dimethylpiperidinium. Gibberellins inhibitor.
Height reduction, earlier maturity and a small yield advantage.
Reduced leaf expansion and shorter main-stem and branch internodes.
Changes in leaf coloration to a darker green and effect on specific leaf weight.
(Oosterhuis et al., 1991)
(Walter et al., 1980; Reddy et al., 1990)
(Gausman, 1980)

19. RESULTS

20. Effect of PGR treatment on growth parameters
Measured at first flower, 2006
Treatment
Height
LAI
Dry Weight cm —
g·m-2
Untreated control
85.18
2.54
352.7
Mepiquat chloride
72.59
1.98
282.6
P-value
0.002
0.007
0.017

21. Effect of PGR treatment on dry matter partitioning
Measured at first flower, 2006
Treatment
Leaves
Stems
Fruit %
Untreated control
40.75
52.19
7.06
Mepiquat chloride
42.63
50.18
7.19
P-value
0.067
0.014
0.894

22. Effect of PGR treatment on light Interception
2006
2007
Intercepted Radiation (MJ·m-2)
2006
2007
Untreated control
204.3
233.0
Mepiquat chloride
201.0
218.4
P=0.463
P=0.012

23. Effect of PGR treatment on canopy extinction coefficient (k)
Across Years
No significant YearRUE interaction (P=0.343)

24. Radiation Use Efficiency
Across Years
No significant YearRUE interaction (P=0.182)

25. Conclusions (Environment)
Radiation use efficiency of cotton grown in Arkansas and California differed significantly in one of the two years of the study and across years.
The California location had higher day temperature, incoming radiation and vapor pressure deficit.
The Arkansas location had higher night temperature and relative humidity.
Increasing vapor pressure deficit decreased radiation use efficiency of cotton by a slope of 0.47 g·MJ-1·kPa-1.

26. Conclusions (PGR) Mepiquat chloride:
Decreased height, leaf area and dry matter of cotton and changed the partitioning of dry matter.
Decreased light interception in 2007.
Increased the canopy extension coefficient (k)
Increased radiation use efficiency in 2006.

27. QUESTIONS ?