Get documents about "Experimental design was a randomized complete block with four replications in a
Shared by: 7P2P287
-
Stats
- views:
- 10
- posted:
- 6/2/2012
- language:
- English
- pages:
- 1
Document Sample
Development of Vegetation Indices as Economic Thresholds for Control of Defoliating Insects of Soybean
James Board Vijay Maka Randy Price Dina Knight Matthew Baur
Department of Agronomy and Environmental Mgmt. Department of Agronomy and Environmental Mgmt. Department of Biological and Agricultural Engineering Center for Geoinformatic Department of Entomology
Louisiana State University, Baton Rouge, LA 70803, USA
Introduction Materials and Methods
■Current criterion for insecticide application : economic threshold 2004 Study
■Labor Intensive : motivated research into alternate methods ■Differences in LAI and light interception were mainly created by manual defoliation. Experimental design was a
■Because insect defoliation reduces yield through light interception randomized complete block with four replications in a split-plot arrangement. Main plots were two commercial soybean
effects on canopy photosynthetic activity and/or crop growth rate, cultivars ‘Asgrow 5902’ (Maturity Group V, determinate growth) and ‘Hartz4998’ (Maturity Group IV, indeterminate growth).
light interception and LAI have been explored as possible Split plots were five defoliation treatments administered during the first week of September, 2004, two weeks after the
economic thresholds for insecticide application. start of seed filling (R5).
■Results indicated that during the first half of the seed filling period, ■Treatments were manual defoliation (random leaf removal) to create the following LAI levels: 1. 0% defoliation (control);
yield was reduced only when defoliation was severe enough to 2. 33% defoliation; 3. 50% defoliation; 4. 66% defoliation; and 5. 100% defoliation. Treatments were administered to six
reduce LAI below about 3.5, a level at which light interception contiguous rows within each plot.
started falling below the optimal 95% level. ■After completion of defoliation treatments all plots were sampled (0.5 m2) for LAI and light interception on 8 Sep.
■Remote sensing techniques that determine canopy reflectance ■Digital images of the plots were recorded on 15 Sep 2004 using a camera system mounted on a pole truck.
ratios (vegetation indices) may be useful in determining critical ■The collected images were converted into NDVI, GNDVI, and SR using Leica Geosystems ERDAS software to process
levels of LAI and/or light interception at which insecticide the digital imagery. Average Red (R), Green (G), and near infra-red (NIR) values were determined as follows: red values
application is justified. were centered at a 670 nm wavelength with a 40 nm bandpass; near infra-red was centered at 800 nm with a 60 nm
bandpass; and green was centered at a 500 nm wavelength having a 40 nm bandpass.
2005 Study
■More cultivars were included in the 2005 study for purposes of detecting possible interactions of Maturity Group (III, IV,
and V) and growth habit (determinate and indeterminate) on relationships between LAI/light interception with vegetation
Objectives indices.
General Objectives ■Differences in LAI and light interception were created by planting date and cultivar in the second year of the study. Plant
■Determine the feasibility of using vegetation indices derived from size generally declines as planting date is delayed from the normal period and cultivar maturity group declines. Our
digital photography to identify areas in a soybean field requiring purpose was to use these two factors to create a wide range of canopy sizes to determine the predictive use of NDVI,
insecticide application for defoliating insects. GNDVI, and SR.
Specific Objectives ■Experimental design was a randomized complete block in a split plot arrangement with four replications. Main plots were
■Determine the relative accuracy of three vegetation indices three planting dates: an optimal planting on 5 May 2005, a moderately late planting on 14 June 2005, and a late planting
CNDVI, SR, and GNDVI for predicting LAI and light interception on 25 July 2006. Splits plots were four cultivars: AG3905 (Maturity Group III), DP4331 (Maturity Group IV), P95M80
across canopies ranging from very low LAI to canopy cover. (MaturityGroup V), and AG5903 (Maturity Group V).
■If accuracy is verified, to develop a system for using vegetation ■Sampling for LAI and light interception occurred near to the mid to late seed filling period for cultivars planted in May, the
indices as economic thresholds based on the normal progression early seed filling period for those planted in June, and the early flowering period for the July planting date. Digital
of LAI and light interception during the seed filling period. photography was accomplished on 26 Aug 2005 near 1200 h using the same method as in 2004.
Figure 1 Figure 2
Data Analysis 4
2004
100 2004
Results
Light Interception (%)
90
y = 2.12 + 5.82x y = 55.0 + 121.0x
■Within both years, correlation and ■Regression relationships between LAI and light interception with NDVI, GNDVI, and SR varied from
R2 = 0.95 80
3 R2 = 0.93
F value: b1 = 159**** 70
F value: b1 = 112****
60
LAI
2 50
regression analyses between 1
40
30
20
linear to quadratic to cubic (Figs. 1-6).
vegetation indices (NDVI, GNDVI, ■Regression relationships between specific vegetation indices with either LAI or light interception were
10
0 0
-0.5 -0.3 -0.1 0.1 0.3 -0.5 -0.3 -0.1 0.1 0.3
NDVI NDVI
and SR) and canopy parameters (LAI 5
2005
100 2005
not homogenous across years, and therefore are presented separately by year.
■Simple linear relationships were shown for LAI and light interception regressed on NDVI in both years
Light Interception (%)
and light interception) were 4
3
y = 1.94 + 3.49x
R2 = 0.97
F value: b1 = 1123****
90
80
70
y = 49.0 + 68.0x
R2 = 0.96
F value: b1 = 937****
60
conducted. Analyses were done for (Figs. 1 and 2) (r2=0.93-0.97).
LAI
50
2
40
30
treatment combinations averaged 1
0
20
10
0
■Green NDVI showed linear relationships with LAI and light interception in 2004, but not 2005
-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8
across replications: defoliation x NDVI NDVI (relationships were quadratic) (Figs. 3 and 4).
Figure 3 Figure 4
cultivar treatment combinations in 4
2004 100
2004 ■The SR showed the most complicated relationships with LAI and light interception, having quadratic
Light Interception (%)
90
y = 0.65 + 8.64x
2004 and planting date x cultivar 3 R2 = 0.95
F value: b1 = 145****
80
70
60
y = 24.6 + 177.0x
R2 = 0.91
F value: b1 = 83****
and cubic relationships in 2004 and 2005, respectively (Figs. 5 and 6).
LAI
2
treatment combinations in 2005.
50
40
1 30
20
Regression analyses were done 0
-0.15 -0.05 0.05
GNDVI
0.15 0.25 0.35
10
0
-0.15 -0.05 0.05 0.15 0.25 0.35
using SAS PROC GLM in which 5
2005
GNDVI
Discussion
linear, quadratic, and cubic
4 y = 3.11 + 2.82x - 12.7x2
R2 = 0.85
100
2005
■For purposes of identifying canopies where light interception falls below 95% (indicating the need for
Light Interception (%)
90
F values: b1 = 174**** y = 71.0 + 71.0x - 208.0x2
3 80
R2 = 0.92
LAI
b2 = 7.2* 70
components were successively
2
1
60
50
40
F values: b1 = 383****
b2 = 10** insecticide), the NDVI was the most appropriate vegetation index to use. The strong linear regressions
of NDVI with LAI and light interception levels ranging from near-total defoliation to canopy closure (95%
30
tested for significance and included if
0
-0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 20
10
GNDVI 0
the residual sum of squares was
-0.5 -0.4 -0.3 -0.2
GNDVI
-0.1 0.0 0.1 0.2
light interception; LAI>4.3, Figs. 1 and 2) demonstrate that this reflectance ratio accurately predicts LAI
Figure 5 Figure 6
significantly reduced (p<0.05). 2004 100 2004
and light interception as these parameters fall from optimal to suboptimal levels. The GNDVI and SR
Light Interception (%)
4
did not maintain linear relationships up to canopy closure as shown by NDVI (Figs. 3-6). For both
90
y = - 70.4 + 158.0x - 42.0x2
2
y = - 3.72 + 7.14x- 1.84x 80
R2 = 0.77
3 R2 = 0.88 70
F values: b1 = 15.9**
F value: b1 = 41*** 60
b2 = 7.2*
■Homogeneity of regression equations
b2 = 12 ** 50
vegetation indices in 2004 and 2005, relationships with LAI and light interception were linear up to an
LAI
2 40
30
LAI of 3.0 and 70% light interception. However, above this level, both canopy parameters showed
20
1
across years for specific vegetation 0
10
0
0 1 2 3
plateau responses to further increases in either GNDVI or SR. Consequently, neither vegetation index
0 1 2 3
SR
index/canopy parameter SR
2005
2005
could distinguish between optimal LAI/light interception levels (3.5-4.0, 95%), and the suboptimal levels
100
Light Interception (%)
relationships was accomplished with
5
90
y = - 1.1 + 4.0x - 1.5x2 + 0.19x3 80
4 R2 = 0.95
70
F values: b1 = 549****
SAS PROC GLM. Homogenous 3 b2 = 10.6**
60
below this when insecticide application is warranted to prevent yield loss.
LAI
50
b3 = 14.5***
40 y = - 16.4 + 95.0x - 36.0x2+ 4.5x3
2
30 R2 = 0.94
regression equations were pooled
F values: b1 = 431****
Conclusion
20
1
b2 = 19****
10
b3 = 19****
0
0
0 1 2 3 4 5
across years. ■Because of its strong linear relationship with LAI and light interception across a broad range of canopy
0 1 2 3 4 5
SR SR
cover, NDVI demonstrated potential use as an economic threshold for identifying canopy parameters
(95% light interception; LAI 3.5-4.0) recognized as indicators for insecticide application during seed
filling.
Related docs
Other docs by 7P2P287
Experimental design was a randomized complete block with four replications in a
Views: 10 | Downloads: 0
