INFLUENCE OF CROP ROTATION, TILLAGE, AND MANAGEMENT INPUTS ON WEED SEED PRODUCTION

Authors: KEGODE, GEORGE - UNIVERSITY OF MINNESOTA; Forcella, Frank; CLAY, SHARON - SOUTH DAKOTA STATE UNIV

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: The number of seeds produced by weeds that escape control is one of the important factors that determine infestation levels in future years. However, little information is available for seed production by escaped weeds. Thus, the consequences of allowing weeds to go to seed are largely unknown. Consequently, a study was conducted from 1990-1994 to determine the effects of crop rotation, tillage, and intensity of weed management on weed density and seed production. The major grass weed was yellow foxtail and the major broadleaf weed was common lambsquarters. As weed density increased the number of seeds produced by individual weeds decreased dramatically, although total weed seed production per acre continued to increase with increasing weed density. Some management systems tended to decrease weed densities and seed production, especially permanent grass pasture. However, a complex rotation involving alfalfa, corn, soybean, and wheat also reduced weed seed production appreciably regardless of the use of various herbicides, especially under reduced tillage. In contrast, continuous corn or corn/soybean rotations that were tilled produced many weed seeds. Two conclusions of this research that are important to farmers are: (1) the consistent negative relationship between weed density and the number of seeds produced by each escaped weed permits easy calculation of the consequences of varying levels of weed control on future weed infestations. This enhances the ability to recommend best treatment during the current growing season. (2) Complex crop rotations under conservation tillage are useful in reducing the ability of weeds to reproduce. This allows farmers to choose rotations that are known to curtail weed seed production.

Technical Abstract: A long-term rotation study, initiated in 1990 and continued through 1994, was conducted to determine the interactions of crop rotation, tillage, and level of management inputs on annual grass and broadleaf weed density, fecundity, and seed production. In all years annual grasses, particularly green and yellow foxtail, were the major weed species and yielded the majority of collected seeds. Grass and broadleaf weed density increased from 1990 to 1994 whereas their fecundity decreased. Most grass seeds were produced in the conventional and ridge tillage systems where production was highest in 1992. Rotations under conservation tillage produced fewer grass and broadleaf weed seeds with no apparent trends. Whereas in conventional and ridge tillage rotations most grass seeds were consistently produced in low input plots, there was little difference in grass seed production among input levels for conservation tillage rotations. In the conservation tillage rotations (corn/soybean/wheat/alfalfa), allelochemicals from wheat and alfalfa residue in combination with reduced tillage and other crop rotation benefits may have caused few grass and broadleaf seeds to be produced in all years except in 1993. Crop rotations that include crops with known allelopathic and competitive activity toward weeds, in combination with reduced tillage, are an effective way of limiting grass and broadleaf weed seed production irrespective of level of management inputs applied.