Abstract: Aims Understanding the response of farmland weed community assembly to fertilization is important for designing better nutrient management strategies in integrated farmland ecological systems. Many studies have focused on weed characteristics, mainly crop–weed competition responses to fertilization or weed communities alone. However, weed community assembly in association with crop growth is poorly understood in the agroecosystems, but is important for the determination of integrated weed management. Biodiversity promotes ecosystem productivity in the grassland, but whether it applies to the agroecosystems is unclear. Based on an 11-year field experiment, the cumulative effects of different fertilization patterns on the floristic composition and species diversity of farmland weed communities along with wheat growth in a winter wheat–soybean rotation were investigated.
Methods The field trial included five fertilization patterns with different combinations of N, P and K fertilizers. Species composition and diversity of weed communities, aboveground plant biomass and nutrient accumulation of weeds and winter wheat, light penetration to the ground surface and wheat yield were measured at each plot in 2009 and 2010. Multivariate analysis, regression and analysis of variance were used to analyze the responses of these parameters to the different fertilization treatments.
Important findings Four dominant weeds (Galium aparine L., Veronica persica Poir., Vicia sativa L. and Geranium carolinianum L.) accounted for ~90% of the total weed density in the 2 years of experimental duration. The residual weed community assembly was influenced primarily by topsoil available nutrients in the order P> N> K. Competition for nutrients and solar radiation between crops and weeds was the main indirect effect of fertilization on the changes in weed community composition and species diversity. The indices of species diversity (species richness, Shannon–Wiener, Pielou and Simpson indices) showed significant linear relationships with wheat yield. The balanced fertilization treatment was more efficient at inhibiting the potential growth of weeds because of solar radiation being intercepted by wheat. These results support the conclusion that wheat yield is favored by balanced fertilization, whereas the weed community is favored by PK fertilization in terms of density and diversity. However, the negative effects on wheat yield may be compromised by simultaneous positive effects of weed communities in the fertilization treatments, for instance, the NP and NK treatments, which are intermediate in terms of increasing wheat production and to a level maintaining a diverse community.

Key words: species diversity, solar radiation, nutrient accumulation, weed communities, fertilization