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Sampling strategy is important for producing weed maps: a case study using kriging

Published online by Cambridge University Press:  20 January 2017

Roger D. Cousens ,
Roderick W. Brown ,
Alex B. McBratney ,
Brett Whelan  and
Michael Moerkerk
Roderick W. Brown
Affiliation:
Department of Earth Sciences, The University of Melbourne, Victoria 3010, Australia
Alex B. McBratney
Affiliation:
Australian Centre for Precision Agriculture, Faculty of Agriculture, University of Sydney, New South Wales 2006, Australia
Brett Whelan
Affiliation:
Australian Centre for Precision Agriculture, Faculty of Agriculture, University of Sydney, New South Wales 2006, Australia
Michael Moerkerk
Affiliation:
Agriculture Victoria-Horsham, Victorian Institute of Dryland Agriculture, P.O. Box 260, Victoria 3401, Australia
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Abstract

Weed maps are typically produced from data sampled at discrete intervals on a regular grid. Errors are expected to occur as data are sampled at increasingly coarse scales. To demonstrate the potential effect of sampling strategy on the quality of weed maps, we analyzed a data set comprising the counts of capeweed in 225,000 quadrats completely covering a 0.9-ha area. The data were subsampled at different grid spacings, quadrat sizes, and starting points and were then used to produce maps by kriging. Spacings of 10 m were found to overestimate the geostatistical range by 100% and missed details apparently resulting from the spraying equipment. Some evidence was found supporting the rule of thumb that surveys should be conducted at a spacing of about half the scale of interest. Quadrat size had less effect than spacing on the map quality. At wider spacings the starting position of the sample grid had a considerable effect on the qualities of the maps but not on the estimated geostatistical range. Continued use of arbitrary survey designs is likely to miss the information of interest to biologists and may possibly produce maps inappropriate to spray application technology.

Keywords

Capeweed, Arctotheca calendula (L.) LevynsGeostatisticskrigingsamplingsurveyrangespacingextentspatial distribution
Type
Research Article
Information
Weed Science , Volume 50 , Issue 4 , August 2002 , pp. 542 - 546
Copyright
Copyright © Weed Science Society of America 

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