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 ( ) MSc Arctic Plant Ecology/Remote Sensing, Univ. of Tromsø (1998) 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

0.5 m

Semi-variance analysis see e.g. Noel A.C. Cressie (1993)

Variogram models Exponential if h = 0 if h > 0

Akaike’s information criterion (AIC) (see e.g. Webster & Oliver 2001)

Prelimnary results distance semivariance WLS,exp,25m ML,exp,full (h) AÎC RpRp 27 21