Abstract: To understand the effects of long-term fertilization regimes on the growth of Beckmannia syzigachne, a dominant wheat-associated weed in wheat field of a rice (Oryza sativa) wheat (Triticum aestivum) rotation system, we carried out an experiment with four fertilization treatments \[no fertilization (CK), chemical fertilizer only (CF), replacement of a portion of chemical fertilizer with composted pig manure (PM), and straw return combined with chemical fertilizer (SF)\] for 10 consecutive years since October 2010. We examined the density of seedlings, tillers and ears during vegetative growth stage, plant height, stem base thickness, length and width of the upper three functional leaves, aboveground biomass, and seed yield during flowering and fruiting stage of B. syzigachne and wheat yield in wheat season in 2019 and 2020. The results showed that the average density of seedlings, tillers, and ears was 84.00 and 115.50, 172.75 and 181.00, 83.00 and 24.25 plants·m^-2 respectively in 2019 and 2020 in treatment CF, which was significantly higher than that in treatments SF and PM. The average plant height, the length and width of the upper three functional leaves were higher in treatment CF than those in treatments PM and SF. The average dry mass was 0.64 and 0.89 g·plant^-1 in 2019 and 2020 in treatment CF, which was significantly higher than that in treatments PM and SF. The average seed yield was 698.10 and 681.30 seeds·plant^-1 in 2019 and 2020 in treatment CF, which was significantly higher than that in treatments PM and SF. Long-term chemical fertilizer application was more beneficial to the growth and reproduction of B. syzigachne, while the combined application of pig manure compost and straw return with chemical fertilizer inhibited the growth and reproduction of B. syzigachne.

Key words: fertilization, dominant weed, density, leaf length, leaf width, shoot biomass, seed yield.