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Spatial biology of weed populations: Influence of abiotic, biotic, and anthropogenic processes
Abstract
Managing weed populations using spatial information is gaining interest because of expected reductions in herbicide use, input costs, and environmental contamination by placing weed control inputs where needed. For short-term decisions, a density distribution map of weed species across a field is required. For long-term strategic decisions, a basic understanding of weed ecology must provide information about the underlying causes for the spatial distribution. The extent to which abiotic, biotic, and anthropogenic processes interact resulting in patchiness of weed populations is unknown and was the focus of this research. Several significant associations were identified using canonical correlation analysis between field-site attributes and weed species abundance in three farmer-managed fields in Iowa and Nebraska. A topographic gradient separated annual grasses found on sand knolls from broadleaf species found in low-lying high organic carbon areas in the Nebraska fields. In Iowa, weed populations in a corn crop were associated with site attributes known to influence plant-available herbicide concentration. Out of this work, several hypotheses were proposed concerning the role of variation in soil fertility, available soil moisture, and herbicide activity as mechanisms causing patchiness. Logistic regression models predicted annual grass and eastern black nightshade occurrence across two Nebraska fields based on two site factors and weed presence in the preceding year. Predictive models for common sunflower and velvetleaf were largely dependent on previous year's presence. Model output has implications for gaining biologically meaningful information from multiple layers of spatial data. Visual patterns of naturally occurring velvetleaf seedling patches were comprised of focal points of high density that decreased with distance from the focal point. This pattern remained consistent before and after weed control and across years, and was attributed to a spatially patterned persistent seedbank, limited seed dispersal, and low seedling survivorship. It was hypothesized that velvetleaf density, per se, had an important role in the observed spatial pattern. Through a number of mechanistic studies, it was observed that a greater number of seedlings survived weed control at higher than lower velvetleaf densities even as weed control intensity increased. This response was a possible mechanism for persistence of patches characterized by patterned internal density distribution.
Subject Area
Agronomy|Ecology
Recommended Citation
Dieleman, Johanna Adriana (Anita), "Spatial biology of weed populations: Influence of abiotic, biotic, and anthropogenic processes" (1998). ETD collection for University of Nebraska-Lincoln. AAI9912684.
https://digitalcommons.unl.edu/dissertations/AAI9912684