Weed dynamics as influenced by tillage system in temperate flooded rice

Purpose: In Europe rice is totally direct-seeded and rice fields are mostly conventionally ploughed. Taking into account the spreading interest of no-tillage in many field crops, in this study we evaluated the influence of this practice both on density and composition of weed community in rice. Approach and methods used: The following tillage systems were compared: conventional ploughing with water seeding (CPW), no-tillage with water seeding (NTW) and no-tillage with dry seeding (NTD). The study was carried out in 2012-2013 at Crescentino, north-west of Italy, in a rice field subdivided in nine plots (3 reps per system) of about 1600 m2 each. Weed assessments were performed in untreated areas within each plot four times during the growing seasons. The initial weed seed bank was determined by taking soil cores at 0-10 cm and 10-20 cm depth. Key results: Weed seed bank was comprised between 1137 seeds/m2 (CPW at 0-10 cm) and 1900 seeds/m2 (NTW at 0-10 cm). The major seed bank weeds were: Cyperus difformis, Lindernia dubia, Eleocharis spp., Echinochloa crus-galli and Ottelia alismoides. In both years, the highest weed density was recorded in CPW (120 plants/m2); NTW and NTD showed a similar density, ranging from 58 plant/m2 (2012) to 83 plant/m2 (2013). Overall, CPW showed a higher number of weed species compared to NTW and NTD. In this system Ottelia alismoides, Cyperus difformis and Heteranthera spp. were the most represented weeds. Echinochloa crus-galli was highly present in all the systems, even though it was more abundant in the no-till systems, particularly in 2013, with plant density often exceeding 80 plants/m2. Weedy rice (Oryza sativa) mainly infested the no-till systems, recording a plant density about two-fold higher in NTD than in NTW. Synthesis and Applications: Weed composition resulted more diversified in the conventional system (CPW), while a reduced number of weed species characterized the other systems (NTW and NTD).