De-inking paper sludge amendment affects weeds in the presence or absence of herbicide in a soybean-corn rotation
The application of de-inking paper sludge (DPS), a C-rich but N-poor soil amendment, can sometimes decrease plant growth. This property needs to be investigated to develop the knowledge and management methods necessary for potential weed control. Today, there is no information on the effectiveness of using DPS to control weeds within a soybean [Glycine max (L.) Merr.]-corn (Zea mays L.) rotation. The objective of this study was to determine the effects of 0, 25, or 50 Mg/ha DPS applied yearly, combined with the absence or the presence of herbicides, on weed abundance and biomass. The experimental sites were St. Augustin de Desmaures for a 4-yr rotation sequence (soybean-corn-soybean-corn) and St. Hyacinthe for a 3-yr rotation sequence (soybean-corn-soybean) in northeastern Canada. Without herbicide and averaged across years, when DPS was applied at 50 Mg/ha DPS, the abundance of annual broadleaf weeds decreased by 78 to 96%, and biomass by 82 to 93%, whereas with herbicide, the abundance decreased by 66 to 100%, and biomass by 80 to 100%, at St. Augustin and St. Hyacinthe, respectively, compared with the 0 Mg/ha DPS treatment. At St. Augustin, DPS applied at 50 Mg/ha without herbicide usually decreased the annual grass weed abundance and biomass. DPS had no obvious effect on the abundance and biomass of perennial weeds. DPS amendment alone or with herbicides suppressed mainly the annual broadleaf weeds, and, to a lower extent, the annual grass weeds.