Wheat yield gaps across smallholder farming systems in Ethiopia

Table 1 Concepts and definitions of the yield levels and yield gaps estimated in this manuscript

Notation	Concept	Definition and reference
Yield levels
Ya	Actual yield	Yield observed in farmers’ fields as a result of growth-limiting and -reducing factors (van Ittersum et al. 2013a);
Y_TEx	Technical efficient yield	Maximum yield that can be achieved for a given input level (Silva et al. 2017);
Y_HF	Highest farmers’ yield	Average yield across top 10^th percentile of actual yields (van Ittersum et al. 2013a);
Ye	Economic yield	Maximum yield with available technology and best-practice management in which marginal costs equal marginal revenue (van Dijk et al. 2017);
Yf	Feasible yield	Maximum yield with available technology and best-practice management but no economic constraints (van Dijk et al. 2017);
Yw	Water-limited yield	Maximum yield of a given genotype when crop growth is limited by water supply (van Ittersum et al. 2013a).
Yield gaps
Yg	Total yield gap	Difference between water-limited yield (Yw) and actual yield (Ya);
Eff. Yg	Efficiency yield gap	Difference between technical efficient yield (Y_TEx) and actual yield (Ya);
Res. Yg	Resource yield gap	Difference between highest farmers’ (Y_HF) or feasible yield (Yf) and technical efficient yield (Y_TEx);
Alloc. Yg	Allocative yield gap	Difference between economic yield (Ye) and technical efficient yield (Y_TEx);
Econ. Yg	Economic yield gap	Difference between feasible yield (Yf) and economic yield (Ye);
Tech. Yg	Technology yield gap	Difference between water-limited yield (Yw) and highest farmers’ (Y_HF) or feasible yield (Yf).

We note these yield levels and yield gaps are only meaningful, and therefore also defined, for a given genotype × environment combination