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Statistics

Comparison of Means of Spatial Data in Unreplicated Field Trials

Dep. of Biological and Agricultural Engineering and Dep. of Plant Sciences, Univ. of California, Davis, CA 95616

^* Corresponding author (replant{at}ucdavis.edu)

Received for publication May 17, 2005. The measurement technologies of site-specific agriculture provide precision instruments at the landscape scale, permitting investigators and farmers to obtain data from experiments in commercial fields at previously unheard of spatial resolution. However, the statistical properties of data arising from these technologies are different from those of traditional small-plot trials data. These differences provide the opportunity to analyze data in different ways. The objective of this paper is to develop a method for estimating the effective sample size and P value of a significance test of the difference between two means in an unreplicated large-scale trial in a commercial field. The method is based on a modification of a well-known correction for spatial autocorrelation of the data when testing the significance of the correlation coefficient between two random variables. An example, the comparison of readings taken from a yield monitor on two different days, is given to demonstrate the properties of the method.

Abbreviations: NDVI, normalized difference vegetation index