Weed–Crop Competition: Which plants benefit more from mineral nitrogen?

Abstract A Mineral Ecological Cropping System (MECS) using mineral fertilizers but no synthetic pesticides has been tested in field trials in Germany over six years. Uncertainty persists regarding whether mineral nitrogen (N) favors crops or weeds under MECS, and this issue was examined in a greenhouse pot study. The study investigated how corn and spring barley, and selected weed species [common lambsquarters and barnyardgrass for corn; blackgrass and common chickweed for spring barley] responded to mineral N. The experiment included crop:weed combinations of 1:0, 1:2, 1:5 and 0:1 for corn, and 1:0, 1:5, 1:15 and 0:1 for spring barley, two representing monocultures, evaluated under four N doses (0N, ½N, 1N, 2N). Data on root and shoot development of weeds and crops were determined at harvest. Increasing N doses increased the biomass of both corn and weeds, while weeds benefited more from the increased N doses than corn. Competitiveness of spring barley against weeds varied with increasing N doses. Blackgrass benefited more from higher N levels than spring barley, while common chickweed was better suppressed by spring barley at increased N. Weed/crop biomass ratios confirmed the observed shifts in competitive balance. The results highlight the importance of effective multi-tactic weed control in MECS.