The impact of variation in grain number and individual grain weight on winter wheat yield in the high yield potential environment of Ireland

Previous studies from regions that produce high proportions of global winter wheat have highlighted that difference in sink size influences the majority of variations in winter wheat yield. However, the potential for source limitation due to environmental differences in regions that consistently produce a large sink capacity (i.e. >20,000 grains/m2), such as Ireland, have not been widely studied. The aim of this study was to characterise the variation in growth pattern and yield components that contribute to variations in grain yield in regions of high yield potential, and to identify the periods of development that are most likely to influence yield in these regions. Monitor crops of winter wheat were grown at three sites with contrasting latitudes on the island of Ireland, during three growing seasons (2013-2015). Crops were assessed regularly for measurements of crop growth and development, including biomass accumulation, canopy development and light interception. Grain yield ranged between 10.7-15.8 t/ha at 15% moisture content, with a grand mean of 12.7 t/ha. Results indicated that variations in grains/m2 had a larger effect on winter wheat yield than variations in individual grain weight. Variability in grains/m2 was influenced by changes in spikes/m2 more than the number of grains/spike. While spikes/m2 at harvest was significantly related to the number of shoots/m2 at GS59, no significant relationship was observed between the shoots/m2 at the time of maximum tillers/plant and spikes/m2 at harvest. Furthermore, a significantly negative linear relationship was observed between shoots/m2 at the time of maximum tillers/plant and grains/spike. Therefore, high rates of tillering were not beneficial to yield formation in the majority of crops monitored. A strong effect of individual grain weight was observed at one site of the nine evaluated in the study, indicating that a partial source limitation of yield is possible in certain Irish environmental conditions. However, variations in grain yield of crops of winter wheat grown at different locations in Ireland in different seasons were primarily driven by variations in grain number, and therefore were generally sink-limited.