The Estimation of the Yield Gap Between Achieved and Potential Winter Wheat Yield Across Ireland Using a Parsimonious Model.

Although Irish winter wheat growers achieve amongst the highest yields of winter wheat globally, annual increases in the average yield of the crop have plateaued in recent times.  However, further yield increases are required to meet demand and to ensure the economic viability of the crop. The aim of this study was to develop a parsimonious model to accurately estimate winter wheat yield potential, and to estimate the difference between potential and achieved yield at contrasting regions across the country. The model inputs are minimum and maximum temperatures, rainfall and total solar radiation on a daily basis for a single growing season.  Canopy size is initially estimated by relating thermal time (expressed in day degrees) to green area index (GAI) empirically, based on benchmark values for development previously recorded from 9 monitor crops across Ireland from 2013-2015. Subsequently, the proportion of light intercepted by the crop is determined based on the GAI estimation, with dry matter production calculated using a benchmark radiation-use-efficiency value (1.55 g DM/MJ solar radiation/m²). The proportion of dry matter available for partitioning to grain is then also determined based on previously observed benchmarks. The average recorded winter wheat grain yields on commercial farms for each of four analysed regions (Carlow, Dublin, Donegal and Westmeath), between 2010-2014, ranged between 9.0–9.4 t/ha at 15% moisture content, whilst the maximum recorded yield in these regions ranged between 10.9-13.0 t/ha, when averaged across 2010-2014. Output from the estimation model indicated that grain yield potential ranged between 15.5-17.5 t/ha during the same period. Therefore, on average, 41-47 % of yield potential is currently not achieved on commercial Irish farms. These results indicate that, based on the incident temperature and radiation levels, significant increases above the current average winter wheat yield are possible in Ireland if current limiting factors can be overcome.