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ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Dairy Forage Research » Research » Publications at this Location » Publication #324063
Title: Field design factors affecting the precision of ryegrass forage yield estimation

Author
item SRIPATHI, RAGHUVEER - University Of Wisconsin
item CONAGHAN, PATRICK - Teagasc (AGRICULTURE AND FOOD DEVELOPMENT AUTHORITY)
item GROGAN, D - Teagasc (AGRICULTURE AND FOOD DEVELOPMENT AUTHORITY)
item Casler, Michael

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/17/2017
Publication Date: 5/5/2017
Citation: Sripathi, R., Conaghan, P., Grogan, D., Casler, M.D. 2017. Field design factors affecting the precision of ryegrass forage yield estimation. Agronomy Journal. 109:858-869.

Interpretive Summary: Field-based agronomic and genetic research relies heavily on the data generated from field evaluations. In turn, farmers rely heavily on university and government field evaluations to rank varieties for use in livestock agriculture. Therefore, it is imperative to optimize the field and statistical methods that are used to rank forage varieties. Using a total of 142 historical ryegrass field trials conducted in Ireland between 2001 and 2011, USDA and Irish scientists identified significant improvements that can be made to Irish ryegrass trials to improve the confidence that farmers have in the published ranking of ryegrass varieties. These improvements are to (1) use square instead of rectangular blocking patterns, (2) use small blocks with few varieties, (3) use smaller plot but employ more plots per variety, and (4) use incomplete block randomization designs in which varieties are grouped in a way to improve the accuracy of direct comparisons between them. These results will be employed by Irish researchers to increase the confidence that farmers have in the lists of variety rankings.

Technical Abstract: Field-based agronomic and genetic research relies heavily on the data generated from field evaluations. Therefore, it is imperative to optimize the precision and accuracy of yield estimates in cultivar evaluation trials to make reliable selections. Experimental error in yield trials is sensitive to several factors, some of which are classified as experimental design factors (i.e. plot size, block size and number of replicates). The objective of this experiment was to conduct a retrospective analysis of long-term perennial ryegrass (Lolium perenne L.) forage yield trials to quantify the effects of block size, block shape, plot size, and number of replicates on trial precision. A total of 142 perennial ryegrass forage yield trials sown between 2001 and 2011 across five locations by the Department of Agriculture, Food and the Marine (DAFM), Ireland, were considered for this analysis. Results from total sum of squares of residuals indicated a decreasing trend in the contribution of row and column sum of squares (SS) with increasing block size from 6 (71% of total SS) to 33 cultivars/block (51% of total SS). The least significance difference decreased with increasing number of replicates only for approximately square blocks indicating the significance of block shape in the DAFM trials. Mean relative efficiency response for increasing block size was significantly higher for square blocks compared to rectangular blocks. Coefficient of heterogeneity (b) was sensitive to increasing block size and number of replicates, but the responses were different between square and rectangular blocks. Results from this retrospective analysis of long-term perennial ryegrass trials indicate that decreasing plot size in conjunction with using incomplete block designs would significantly improve precision for the DAFM trials.