Proceedings of the Sixty-first Annual Meeting of the Northeastern ...

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ENHANCED TOLERANCE TO WEED COMPETITION: EFFECTS OF CROP AND
SOIL MANAGEMENT IN A LONG-TERM CROPPING SYSTEMS TRIAL. M.R. Ryan,
The Pennsylvania State Univ., University Park and The Rodale Institute, Kutztown, PA,
D.A. Mortensen, S.B. Mirsky, The Pennsylvania State Univ., University Park, D.O.
Wilson, R.M. Seidel, and P.R. Hepperly, The Rodale Institute, Kutztown, PA.
ABSTRACT
Long-term cropping systems trials systems provide unique opportunities to
explore the effect of crop and soil management on crop-weed competition. The
Farming Systems Trial (FST) was initiated in 1981 and compares a conventional
management system with a corn-soybean rotation to two organic management
systems. One organic system represents a dairy operation with a corn, soybean,
wheat, and hay rotation, and uses manure as a nitrogen source for corn. The other
organic management system represents a cash corn, soybean, wheat system without
livestock, and uses legumes as a nitrogen source.
Over the 26 year history of the FST, the conventional and organic-livestock
systems produced similar corn and soybean yields while the organic-legume system
averaged approximately 10% lower yield (corn yields: 7460, 6718, and 7439 kg ha -1 ;
soybean yields: 2332, 2213, 2434 kg ha -1 for the organic-livestock, organic-legume, and
conventional systems respectively). At the same time the two organic systems
averaged 4-5 times greater weed biomass than the conventional system.
To explore the apparent increased weed tolerance in the organic systems, an
experiment was conducted to determine if differences exist in crop-weed competition
relationships in corn and soybean across systems. Density of mixed weed species was
manipulated to achieve four levels ranging from weed free to a heavy infestation. Weed
density and biomass at peak accumulation was used as a measure of weed infestation.
The rectangular hyperbola model was fitted to data from each system. Crop yield loss
as a function of mixed weed density was higher in the conventional system.
Descriptive models of weed competition on crop yield were fit using best subsets
multiple regression to determine the competition effect of individual weed species to
corn and soybean yield across systems. The rectangular hyperbola model was
manipulated to explore the intensity of competition of individual weed species across
systems. Preliminary analysis indicates that crop and soil management system
differentially influences the competitive ability of weed species. Other mechanisms
responsible for overall difference in crop yield loss as a function of weed density are
perceived to be soil mediated crop production capacity.
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