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