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RESEARCH PRODUCT

Soil weed seedbank composition and structure in a long-term nutrient management experiment

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description

EAGESTAD; Weed communities can be influenced by nutrient availability, nutrient form (e.g. ammonium vs. nitrate), amendment timing, amendment type, and by immigration of seeds during amendment applications. New York ranks third in the United States in the number of dairy cows and thus dairy manure applications are prevalent throughout the state. The objective of this work was to compare the effect of dairy manure and inorganic fertilizer on soil weed seedbank composition and structure in a long-term nutrient management experiment. The field experiment was initiated in 2001 at the Cornell Musgrave Research Farm in Aurora, NY and compared ten treatments in a corn-alfalfa rotation using a randomized complete block design. We hypothesized that weed species, communities, and species traits would differ between amendment treatments. In 2015, we quantified the soil weed seedbank in five of the ten treatments: 1) liquid dairy manure (138 m3/ha); 2) composted separated dairy solids (84 T/ha); 3) inorganic N as starter fertilizer (22 kg N/ha); 4) inorganic N as starter fertilizer (22 kg N/ha) and sidedress fertilizer (146 kg/ha N); and 5) inorganic N as starter fertilizer (22 kg N/ha) and sidedress fertilizer (247 kg N/ha). A total of 30 soil cores were collected before spring weed germination and prior to corn planting at a depth of 20 cm in five replicates in each of the five treatments. Soil (1.2 kg) was placed on top of a thin layer of vermiculite in a black plastic tray (25 x 25 cm) and watered routinely in a greenhouse germination bioassay. Weed seedlings were identified, counted, and removed. After emergence ceased, the soil was dried, homogenized, and the process was repeated. No treatment differences in weed species richness or total weed abundance were observed. However, multivariate analyses of the weed community and species traits showed clear assemblages that varied by treatment. Plots with lower soil fertility favored nitrophilic, light-loving monocotyledons and basic-soil, moderate light-loving dicotyledons, whereas plots with higher soil fertility favored moderate shade-loving perennial hemicryptophytes. These results contribute to a body of literature on weed community assembly and could be useful for optimizing nutrient management for weed suppression and other goals such as conservation of biodiversity.