Influence of crop height on harvesting losses in windrowed wheat

Harvesting losses in windrower/combine and direct combine harvesting systems were measured in four spring wheat (Triticum aestivum L.) genotypes during 5 yr. Two of the cultivars were of conventional height and two were semidwarfs. Crop height varied among years due to precipitation differences, and ranged from 49 to 90 cm in the conventional-height genotypes HY355 and Neepawa and from 39 to 70 cm in the semidwarfs HY320 and HY912. Total harvesting losses for the windrower/combine system were greater for the semidwarf than for the conventional-height genotypes because of higher combine pick-up losses in the semidwarfs. Pick-up losses increased as crop height decreased (pick-up loss = 17.01 − 0.42 × height + 0.003 × height 2 , R 2 = 0.86) in both the conventional-height and semidwarf genotypes. Pick-up losses increased markedly below a threshold height of approximately 60 cm. Total losses for the direct-combine system were lower than those of the windrower/combine system; in very short crops this advantage was maintained even when direct combining was delayed for 2 wk beyond combine ripeness. Direct combining is recommended in crops less than 60 cm in height. Semidwarf genotypes are shorter than this threshold more frequently than conventional-height genotypes.Key words: Direct combining, Semidwarf, Combine pick-up loss, natural shattering loss