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Spatial variation of weed density in a small cereal field
Therese With Berge
PhD student, Herbology, Plant Protection Centre, The Norwegian Crop Research Institute (3.5 yrs)
Research Assistant, sub Arctic vegetation/remote sensing, N Sweden (1998-2000)
MSc Arctic Plant Ecology/Remote Sensing, Univ. of Tromsø (1998)
www.planteforsk.no
My background
PhD work
• Defining/improvement of broadleaf weed damage threshold models in spring cereals
• Competition experiments at field scale
• Weed position mapping – geostatistical analysis
Spatial variation of weed density in a small cereal field
Why?
• Weeds are often heterogenously distributed
• Herbicides should be applied only where needed
• Detection and spraying at same time
Specific questions:
• How close should measurements of weeds be taken in the driving direction?
• How wide can a presicion spray boom be?
Methods
• Counting within frames
• Geostatistical analysis
Mapped site
2 m
1
.5
3 m
0.5 m
0.5 m
Semi-variance analysis
)()(
2)()()(2
1)(ˆ
hNssji
ji
sZsZhN
h
see e.g. Noel A.C. Cressie (1993)
Variogram models
Rhecch
/10 1
0)(
Exponential
if h = 0
if h > 0
Akaike’s information criterion (AIC)
(see e.g. Webster & Oliver 2001)
pMnnn
nAÎC 2ln22
ln
Prelimnary results
0 10 20 30 40
0.0
0.2
0.4
0.6
0.8
distance
semivariance
WLS,exp,25m
ML,exp,full
(h)
AÎC
-30.7
-68.8
Rp
27
21