tTo increase wheat productivity from current levels, the yield gap, the difference between actual andpotential yield, should be analyzed. A crop model was calibrated for three winter wheat cultivars andvalidated for a major wheat growing area to evaluate yield gaps in Khorasan province in northeasternIran. The validated model was used to simulate long-term yield for 14 locations under three man-agement conditions (potential, water-limited, nitrogen-limited). The results showed that the averagesimulated potential yield of 7.8 Mg ha−1has not yet been realized by farmers and there is a large gapbetween the actual and potential production levels (about 5.2 Mg ha−1). The simulation showed consid-erable difference between cultivars for yield gap. When averaged over locations and seasons, the totalyield gap obtained for Chamran wheat was 4.4 Mg ha−1, for Sionz was 6 Mg ha−1, and for Gascozhen was6.1 Mg ha−1. Across locations, the proportion of yield gap from water-limitation was 1.7% to 19.5% and fornitrogen- limitation was 40% to 47%. The gap caused by other limiting and reducing factors was 33–57%.The highest yield gap was observed in Ghaen for Gascozhen (7.6 Mg ha−1) and the lowest was observed inSarakhs for Chamran (3.1 Mg ha−1). The results of the study suggest that the average farm yield of about2.6 Mg ha−1in irrigated fields in Khorasan province is not limited by low genetic yield potential. Thisindicates that farmers should emphasize more on management factors such as water availability, timingof nitrogen application, and selection of cultivars adapted for each environment to reduce yield gap.

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