The Association of Weed Species Richness and Abundance with Field Margin Type in Crop Fields

Abstract

Natural vegetation on farms such as field margins, successional fallow fields, ditch systems, and neighboring forests provide increased biodiversity, structural diversity, habitat for wildlife and beneficial insects, and can act as protective buffers against agrochemical drift. Nevertheless, farmers frequently view these areas as potential sources of weeds, insect pests, and diseases. Objectives of this study were to examine weed species richness and abundance in cropland bordered by managed versus unmanaged field margins to determine if differences in weed infestation exist. Weed abundance and richness were measured in crop fields along permanent transects that extended from the field edge to the center of the crop fields. Presence/absence data for all plant species in the field margin were also recorded.

Transect data from fields with margins of natural vegetation were compared to transect data from fields with managed margins using analysis of variance. There were no differences between log total abundance of weeds in crop edges adjacent to managed and unmanaged field margins (P=0.44). For both margin types, more weeds were found near the field edge than in the center of the field (1.37±0.08 to 0.52±0.07 and 1.39±0.07 to 0.41±0.06, for managed and unmanaged field margins respectively). Species richness was slightly higher along crop edges of managed field margins (7.35±0.32) than crop edges along unmanaged field margins (6.55±0.31).

Across all sampling dates, a total of 105 plant species were identified in the field margins. Of these species, 42 (40% of all species) were found somewhere in a field when all sampling dates were pooled. Managed field margins had lower species richness than unmanaged field margins - less than half the mean number of species (5.8±0.28 versus 14.7±0.62 species, respectively).

No association was found between plant species occurring in the field margin and in the crop field by generating 2 x 2 contingency tables via PROC FREQ and testing the association with Fisher's exact two-sided test. Using logistic regression via PROC GENMOD, margin type and weed presence in the field margin were not effective predictors of weed occurrence in the crop field.

KEYWORDS: field margin, weed populations, crop edges, farm natural areas