1997 Crops Day Report

INTERPRETING STATISTICAL ANALYSIS

Field research involves the testing of one or more variables such as crop varieties, fertilizers, tillage methods, etc. Field testing of such variables are conducted in order to determine which variety, tillage method, or fertilizer etc. is best for the particular area of production. The main objectives of crop production research are to determine the best means of producing the crop and how to maximize yield and economic return from farming.

Agricultural researchers use statistics as a tool to help differentiate production variables so that real and meaningful conclusions can be drawn from a relatively large amount of data.

One of these tools is the Coefficient of Variability (C.V.). This statistic gives an indication of the amount of variation in an experimental trial. Trials conducted at Hettinger use four replications or repetitions of the variable in question. For example, the variety Amidon HRSW appeared four times (four replications) in the HRSW variety trial. In this case, the C.V. for yield of the Hettinger HRSW variety trial on fallow was 8.1%. This C.V. is a relative measure of how much the yield of all HRSW varieties varied between replications. In other words, C.V. is a measure of the precision or effectiveness of the trial and procedures used in conducting the trial. More can be said about a field trial with a relatively low C.V. (10 or less) than one with a C.V. greater than 10. Attempts are made to control human error and some environmental conditions such as conducting field studies on a uniform soil so that variability between replicates is minimized with a resulting low C.V. value (10 or less). In summation, a trial with a C.V. of 8 is more precise and more can be concluded from it than a trial with a C.V. of 18.

Another important statistical tool is the Least Significant Difference or LSD. If the yield of variety A exceeds variety B by more than the LSD 5% value you can conclude that under like environmental conditions, variety A will significantly out-yield variety B 95% of the time. The LSD value allows you to separate varieties, tillage practices, or any other variable and determine whether or not they are actually different. The LSD 1% value is always larger than the value for LSD 5% and is used in the same manner. If the yield of variety A exceeds variety B by more than the LSD 1% value you can conclude that under like environmental conditions, variety A will significantly out-yield variety B 99% of the time. Little confidence can be placed in variety or treatment differences unless the results differ by more than the LSD value.

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