In Iran, currently about 23% of wheat farms have more than 5ton/ha yield, while the technology and the capacity of over 85% of the existing combine harvesters are low and not suitable for such yield. These combines are not able to work properly in a high-yield field, because of their extremely high harvest losses and the blockage of threshing unit mainly, due to high feed rate. Therefore, it is necessary to match them to the farms for a better performance through optimizing their feed rate either by changing the effective width of cutterbar or the ground speed. However, simply reducing the effective width of cutterbar, which is now the common method in some districts, may also affect the fuel consumption and field capacity of combine with more likely higher seed breakage. This paper develops a proper technical framework for wheat harvesting of high-yield fields using low-capacity combine harvesters based on multi-criteria decision making (MCDM) techniques. Several attributes mainly, seed breakage, total harvest losses, fuel consumption, and combine field capacity were considered as technical attributes. Nine different combinations of ground speed and effective width of cutterbar were defined as candidate alternatives. The experiments were conducted in Khorasan province of Iran in 2007 and the corresponding data related to the attributes were calculated. Based on these data the multi-criteria analysis was discussed and a decision assistant model developed. In general, the decision making process indicated that the common method which simply reduces the effective width of cutterbar is not the most suitable solution for harvesting high yield fields with old combines. Instead, this framework introduced the combination of 3.5km/hr ground speed and the entire use of platform as the best alternative for harvesting a field with average yield of 7.4 ton/ha wheat cultivar (Shiraz), while the seed moisture content and the ratio of Grain/MOG were 7.5% and 1.02% respectively.

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