DOI: 10.1111/j.1365-3180.2012.00929.x Seed losses at harvest and seed persistence of oilseed rape (Brassica napus) in different cultural conditions in Chinese farming systems Y M ZHU*, Y D LI  , N COLBACH à , K P MA*, W WEI* & X C MI* *State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, The Chinese Academy of Sciences, Xiangshan, Beijing, China,  Institute of Agricultural Engineering, Jiangxi Academy of Agricultural Sciences, Nanchang City, Jiangxi Province, China, and àINRA, UMR1347 Agroe ´cologie, ECOLDUR, Dijon, France Received 15 October 2011 Revised version accepted 10 April 2012 Subject Editor: Peter Lutman, UK Summary This article reports experiments that explore the critical factors for gene flow in oilseed rape (Brassica napus) via the soil seedbank under Chinese farming systems. Research was carried out on 16 farmerÕs fields to estimate harvest seed losses after different planting methods and harvest timings, during the four compo- nents of the harvest operations. An additional field experiment was set up to estimate the potential germi- nation proportion of seeds in flood-irrigated and un- irrigated fields, as a function of seed burial depth over time. Seed losses were largest during the sun-drying of harvested plants in the field, accounting for about three quarters of the total seed losses. The number of intact seeds declined quickly after they entered the soil, particularly in un-irrigated fields, and no volunteers germinated in the irrigated field after 3 months. Burial depth did not affect the potential for germination and emergence of volunteers in the flood-irrigated field. However, the potential germination declined with increasing burial depth in the un-irrigated field. No viable seeds remained in the soil after 16 months. Seed losses during harvest could be limited to 0.7–1.1% by weight of total seed production by placing a plastic membrane under the cut plants during drying and no rape seeds could germinate after 3 months in water- logged condition. Thus, the risk of gene flow via the soil seedbank is probably small in Chinese oilseed rape farming systems. Keywords: volunteers, seed losses, intact seeds, potential germination proportion, seed dormancy. ZHU YM, LI YD, COLBACH N, MA KP, WEI W&MI XC (2012). Seed losses at harvest and seed persistence of oilseed rape (Brassica napus) in different cultural conditions in Chinese farming systems. Weed Research. Introduction In farmland, seed losses of oilseed rape (Brassica napus L.) during harvest are the main source of soil seedbanks. In Europe, harvest seed losses range from 2% to 5% of the yield even in optimal conditions (Price et al., 1996) and can reach up to 50% if harvesting is delayed, or after bad harvesting conditions (Macleod & Green, 1981). These shed seeds can acquire secondary dormancy in the soil seedbank, if they experience unfavourable conditions for germination, such as water stress or ⁄ and oxygen defi- ciency (Pekrun et al., 1997a; Momoh et al., 2002). They can survive for up to 10 years (Schlink, 1998). Conse- quently, these seeds can give rise to volunteers in subsequent crops (Gruber & Claupein, 2007). For instance, volunteer plants have been found 5–9 years after harvest of the last oilseed rape crop, both in Europe (Pessel et al., 2001) and in North America (Simard et al., Correspondence: X Mi, State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, The Chinese Academy of Sciences, 20 Nanxingcun, Xiangshan, Beijing 100093, China. Tel: (+86) 10 62836507; Fax: (+86) 10 82596146; E-mail: mixiangcheng@ibcas.ac.cn Ó 2012 The Authors Weed Research Ó 2012 European Weed Research Society Weed Research