Weed-Crop Competition

Nitrogen levels and weed competition in soybean

Why study weeds?
Organic farmers have indicated that weed competition is a major concern. Although spraying and tillage are two methods of managing weeds, we wanted to explore reducing weeds’ competitive ability through an ecological framework. Previous research suggests that crops are more competitive against weeds (ie. more able to “tolerate” weeds) in organically managed compared with conventional growing systems. Many factors may contribute to this pattern, including plant resource-partitioning abilities, plant-microbe associations, and other ecological relationships.

The experiment
We conducted field experiments to quantify soil nitrogen pools and weed competition with soybean across varying soil management systems within the Cornell Organic Grain Cropping System Experiment at the Musgrave Research Farm in NY. We investigated the effects of soil management and Nitrogen pool diversity on weed-crop competition. By describing poorly understood ecological mechanisms and feedbacks, our research aimed to assist the development of new integrated weed management strategies that reduce the need for herbicides and mechanical cultivation.

We compared four organic management systems in terms of weed suppression, weed community composition, and weed-crop competition in soybean. The four systems approaches were High Fertility (“maximize yield with more inputs”), Low Fertility (“maximize profit with fewer inputs”), Enhanced Weed Management (“improve long-term results with fewer weeds”), and Reduced Tillage (“improve long-term results with improved soil”).

The Reduced Tillage system had the highest weed biomass (~1200 kg/ha). Low Fertility and Enhanced Weed Management systems had lower weed biomass (~200 kg/ha). Across all systems there was an average 9% soybean yield loss due to weeds. We concluded that the Low Fertility system was the most favorable for soybean, due to its competitive yield, good weed suppression, and low input costs.

View our presentation on weed competition in soybean for the Northeast Weed Science Society of America January 2015 meeting

Read Margaret Ball’s thesis on weed-crop competition


Soil-mediated cropping diversity effects on crop-weed competition

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