Data rich yield gap analysis of wheat in Australia

- Data rich yield gap analysis was conducted for wheat in Australia during 1996-2010.
- Australian wheat growers are achieving 49% their water-limited yield potential.
- The yield gaps tended to be larger where water-limited yields were higher.
- The causes of spatial variability of relative yield gaps require further research.
- Results are remarkably similar to data-limited Global Yield Gap Atlas protocol results.

Closing the gap between yields currently achieved on farms and those that can be achieved with best practice and current technology in a given environment is a key strategy for increasing grain production on existing cropland. In this study, the yield gap of rainfed wheat in Australia was derived by a data rich (DR) analysis method made possible by the high density of data available in the Australian grain zone. At the national scale, the analysis revealed that Australia's 15 year (1996-2010) average actual wheat yield (Ya) was 1.7 t/ha, while the simulated water-limited yield potential (Yw) was 3.5 t/ha; thus the yield gap (Yg = Yw-Ya) was 1.8 t/ha; and the relative yield (Y% = 100 x Ya/Yw) was 49%. The fifteen year average Ya and Yw values for each of the 245 statistical local areas (SLAs) in Australia's wheat zone were strongly and positively correlated (Ya = 0.456 x Yw + 0.15; R2 = 0.65; RMSE = 0.291; p < 0.001) such that the yield gap (Yw-Ya) tended to be larger in SLAs with higher Yw values. Mean Y% values vary among SLAs from a low of 34% to a high of 69% (standard deviation = 7.7%). The extremely tight correlation, at the national scale (Ya = 0.488 x Yw + 0.021; R2 = 0.95; RMSE = 0.087; p < 0.001), between the methodologically independent estimates of Yw and Ya values points to the consistency of both estimates. It also indicates the potential for using updated Yw estimates to help derive more reliable national crop yield forecasts in real time. The results of this analysis were compared with those of two alternative analyses of Australia's wheat yield gaps using (1) EarthStat, a statistically based global yield gap analysis methodology and (2) the Global Yield Gap Atlas (GYGA) designed to achieve locally credible assessments of yield gaps for developing regions such as sub-Saharan Africa (SSA) and South Asia (SA) with the limited data typically available in such countries. At the national level all three methods gave similar results. However, at the sub-national level (based on agroecological zones) differences emerged between the water-limited yield potential values of EarthStat on the one hand and those of the DR and GYGA methods on the other. Given the high spatial environmental variability within the Australian wheat zone the remarkable level of agreement between results from these two methodologies provides evidence of the robustness of the GYGA protocols. The advantage of the DR method is in its higher resolution and the subsequent local relevance of results.