Seed losses in commercial harvesting of oilseed rape

Significant seed losses occur in oilseed rape due to natural shedding and crop disturbance by harvesting machinery. Measurements were made in spring and winter sown rape to determine amounts lost by natural shedding from standing crop and ripening swaths and from the machine operations for a direct cut crop and a swathed crop. Combine threshing and separation losses were not measured. A randomized plot experiment compared losses from a direct cut and a swathed crop when harvested at the recommended agronomic stage of maturity and at a later date. Samples of losses occurring from ripening crop and as a result of the harvesting process were measured. Trays placed in the standing crop and beneath ripening swaths collected naturally occurring losses. Trays placed in the crop beneath working machines collected losses from direct cutting, swathing and picking up by swaths by undercutting or the use of a draper (tined conveyor) pick-up. During direct cutting and swathing, groups of trays in carefully selected locations collected seed shed by the side knife, cutterbar and central area of the headers where crop is brought together before entering the elevator or forming the swath. Overall losses in winter rape were around 11% for direct cutting at both recommended and late timings, of which 4.7% to 6.4% were from natural shedding. In the swathed crop, losses ranged from 10.7% to 24.8%, with much lower natural shedding losses of zero to 1.8%, the highest losses resulting from the late swathing operation. Overall losses in spring rape were 1.7% to 4.9% for direct cutting with natural shedding losses of 1.2% to 2.0% and overall losses of 2.6% to 4.6% for the swathed crop, with natural shedding losses of zero to 0.9%, the recommended timing giving the lowest losses. (C) 1996 Silsoe Research Institute