Comparing Variety Trial and Commercial Data: Trends and Relationships for Practical Use in the South African Sugarcane Industry

The Variety Evaluation Project at SASRI involves conducting variety trials throughout the South African sugar industry. A general trend is that trial yields consistently exaggerate commercial yields obtained by growers under the same conditions. The objective of this study was to use historic variety trial and commercial yield data to evaluate the possibility of using correction factors and plot yield estimates to obtain more realistic and better estimates of commercial performance. Additionally, trial data were used to investigate the possibility of using destructive sampling to estimate trial plot yields. Trial yields consistently followed the same trends as commercial yields since initiation of the project. However, trial yields were on average 30 t/ha more than commercial yields. A correction factor of 0.7 was identified as being appropriate for adjusting trial yields to those of average commercial levels across the sugarcane industry. A suitable correction factor was subsequently calculated for each mill area in the industry (these ranged from 0.54 to 0.9). Offstation trial yields were more consistent with commercial trends than on-station trials. A significant exponential relationship (r=0.7) was found between actual plot yields and estimated yields from destructive sampling. Applying a correction factor to estimated yields adjusted the data to correspond with commercial levels. This indicated that destructive sampling, followed by the application of a correction factor, may be an acceptable way of determining realistic trial yields when actual harvesting of trials cannot be done. These results will assist in optimising recommendations derived from the Variety Evaluation Project.