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@ARTICLE{Rudolph:820901,
      author       = {Rudolph, S. and Wongleecharoen, C. and Lark, R. M. and
                      Marchant, B. P. and Garré, S. and Herbst, M. and Vereecken,
                      H. and Weihermüller, L.},
      title        = {{S}oil apparent conductivity measurements for planning and
                      analysis of agricultural experiments: {A} case study from
                      {W}estern-{T}hailand},
      journal      = {Geoderma},
      volume       = {267},
      issn         = {0016-7061},
      address      = {Amsterdam [u.a.]},
      publisher    = {Elsevier Science},
      reportid     = {FZJ-2016-06165},
      pages        = {220 - 229},
      year         = {2016},
      abstract     = {In experimental trials, the success or failure of
                      agricultural improvements is commonly evaluated on the
                      agronomic response of crops, using proper experimental
                      designs with sufficient statistical power. Since fine-scale
                      variability of the experimental site can reduce statistical
                      power, efficiency gains in the experimental design can be
                      achieved if this variation is known and used to design
                      blocking, or some proxy variable is used as a covariate.
                      Near-surface geophysical techniques such as electromagnetic
                      induction (EMI), which describes subsurface properties
                      non-invasively by measuring soil apparent conductivity
                      (ECa), may be one source of this information. The motivation
                      of our study was to investigate the effectiveness of
                      EMI-derived ECa measurements for planning and analysis of
                      agricultural experiments. ECa and plant height measurements
                      (the response variable) were taken from an agroforestry
                      experiment in Western Thailand, and their variability was
                      quantified to simulate multiple realizations of ECa and the
                      residuals of the response variable from treatment means.
                      These were combined to produce simulated data from different
                      experimental designs and treatment effects. The simulated
                      data were then used to evaluate the statistical power by
                      detecting three orthogonal contrasts among the treatments in
                      the original experiment. We considered three experimental
                      designs, a simple random design (SR), a complete randomized
                      block design (CRB), and a complete randomized block design
                      with spatially adjusted blocks on plot means of ECa
                      (CRBECa). Using analysis of variance (ANOVA), the smallest
                      effect sizes could be detected with the CRBECa design, which
                      indicates that ECa measurements could be used in the
                      planning phase of an experiment to achieve efficiencies by
                      improved blocking. In contrast, analysis of covariance
                      (ANCOVA) demonstrated that substantial power improvements
                      could be gained when ECa was considered as a covariate in
                      the analysis. We therefore recommend that ECa measurements
                      should be used to characterize subsurface variability of
                      experimental sites and to support the statistical analysis
                      of agricultural experiments.},
      cin          = {IBG-3},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IBG-3-20101118},
      pnm          = {255 - Terrestrial Systems: From Observation to Prediction
                      (POF3-255)},
      pid          = {G:(DE-HGF)POF3-255},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000369473100024},
      doi          = {10.1016/j.geoderma.2015.12.013},
      url          = {https://juser.fz-juelich.de/record/820901},
}