Comparison of Experimental Designs Used to Detect Changes in Yields of Crops Exposed to Acidic Precipitation1
- Lance S. Evans and
- Keith H. Thompson2
A comparison of experimental designs used to detect changes in yield of crops exposed to simulated acidic rain was performed. Seed yields were determined from field-grown soybeans (Glycine max L.) exposed to simulated rainfalls in which all ambient rainfalls were excluded by automatically moveable rainfall exclusion shelters. When all eight, 4 ✕ 4 , latin squares were used, simulated rainfalls of pH 4.1,3.3, and 2.7 exhibited yields 10.6,16.8, and 23.9%, respectively, below yields of plants exposed to pH 5.6. The linear component of pH treatment differences showed a highly significant decrease in yield (p < 0.001). The eight latin squares analyzed as individual experiments yielded erratic conclusions. However, when all eight latin squares were combined a satisfactory evaluation can be made. The low probability value for differences among latin squares (p < 0.005) indicates that field locations are a legitimate source of stratification. Sources of variation are also highly significant for both pooled among rows within squares (p = 0.0028) and the pooled among columns within squares (p = 0.0168) indicating that the two stratifications within each latin square was doubly effective in reducing the residual error term. The relative efficiency of the latin square to a randomized complete block design, and a completely randomized design was 132-146 and 162%, respectively.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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