Spatial Analysis of Forage Grass Trials across Locations, Years, and Harvests
- K. F. Smitha and
- M. D. Casler *b
Spatial analyses of yield trials are a powerful method of adjusting treatment means for spatial variation and improving statistical precision of mean estimation. Because yield trials are typically repeated across multiple locations and years, spatial analysis methods must be adapted for combined analyses across locations and years. The objective of this study was to evaluate the relative efficiency of nearest neighbor analysis (NNA) across locations and years for several perennial forage grass trials. Three spatial adjustment methods were developed: preadjustment based on total forage yield, postadjustment based on total forage yield, and preadjustment based on forage yield of individual harvests. For cool-season grasses on a multiple-harvest management, NNA had relative efficiencies of 105 to 135% across locations, years, and trials. Within trials, there was some consistency across harvests, resulting in greater improvements in precision for adjustment based on total yield. Across locations and years, the three spatial adjustment methods always ranked the same in relative efficiency: preadjustment by harvest > preadjustment of total yield > postadjustment of total yield. The advantage of the preadjustment methods was likely due to fitting heterogeneous slopes (adjustment factors) across locations, years, and/or harvests. In contrast, trials with a single-harvest management for biomass production always had relatively low relative efficiency of NNA. Trial operators should assess the relative efficiency of NNA on early harvests from all locations within a trial and if the relative efficiencies are large, they should consider the use of NNA across locations and years to adjust entry means.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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