Research Accomplishment Reports 2009

Weed Management Strategies for Sustainable Cropping Systems

L.J. Grabau
Department of Plant and Soil Sciences

 

Non-Technical Summary

Weed management is generally viewed as a major challenge in conventional, transitional and organic cropping systems. Control of weeds in agriculture costs the U.S. economy more than $15 billion annually, more than the cost of controlling insects and diseases combined. Although organic cropping systems are often highly profitable anyway, weed densities frequently boarder on or exceed tolerable levels, and surveys of organic growers and studies of organic farms indicate that weeds are a major production problem. Moreover, existing methods for controlling weeds on organic farms depend on excessive soil disturbance, resulting in loses in soil quality.

Currently, little research is directed toward the weed management needs of organic producers. New methods like organically certifiable herbicides and weed management with cover crops are needed. There is also a need to evaluate existing approaches like nutrient management for weed control and the mechanisms of cultivator action.

Conversations with growers indicate that fear of uncontrolled weeds is frequently a factor inhibiting adoption of organic practices. Development of new weed management methods and improvement of traditional methods will speed adoption of organic practices, thereby reducing use of both herbicides and other pesticides. This will improve environmental quality and reduce expenses for farmers. Better weed management options will also improve yield and profits, thereby strengthening local communities.

2009 Project Description

The primary output of this project in 2009 was the development of two outstanding USDA Sustainable Agriculture Interns, namely Josiah Frey and John McMaine. These two University of Kentucky students worked diligently on the projects described and developed remarkable levels of expertise in sustainable agriculture research methodologies. Both conducted their own independent research projects, and presented their results at the annual meetings of the American Society of Agronomy in Pittsburgh, PA in November of 2009.

2009 Impact

Perhaps the most important single outcome of the project for 2009 was the differential impact of tillage systems on weed control in organically produced soybean. Soybean planted into no-till rye (using the unique front-mounted crimper-roller system) produced much higher average yields than did soybean planted into a conventionally tilled seedbed on the same day. In addition, the critical weed-free period, generally shown to be about 4 weeks for most grain crops, was only 2 weeks for no-till soybean but was 6 weeks for conventionally-tilled soybean. We intend to repeat this study in 2010 in order to evaluate the repeatability of this result.

Organic grain cropping systems depend on a dramatically different set of crop production inputs than do conventional grain cropping systems. Fertility and weed control are two prime examples of the differences involved. There also may be subtle or sharp input differences required to effectively manage diverse organic grain cropping systems. The objective of this research was to compare corn (Zea mays L.) productivity under three divergent organic cropping systems, each including a two-year rotation, with each crop element of each rotation present each year. Systems tested in 2004-08 near Lexington, KY were as follows:

a) corn following 18 months of orchard grass/red clover mixed forage,

b) corn following hairy vetch, rotated with soybean following winter rye, and

c) corn following winter wheat and double crop soybean.

Corn was established in each system utilizing conventional tillage and 45 kg ha-1 N (as Nature SafeTM) applied at growth stage V4. At growth stage V8, additional N was applied at rates of 0, 45, 90, and 135 kg ha-1. Weed control measures included 1-2 mechanical cultivations plus hand-hoeing of any noxious weeds (johnsongrass, Canada thistle) which were noted. At physiological maturity, biomass samples were collected for corn and grass and broadleaf weeds. Yields and yield components will be reported. Organic grain cropping systems appear to result in differing corn productivity and to require different management strategies.

2009 Publications

Grabau, L. J., F. C. Oad, and L. C. Harris. 2009. Comparisons of organic grain cropping systems in Kentucky. American Society of Agronomy National meeting abstracts, available at www.agronomy.org, verified Jan. 5, 2010.

Suarez, A., and L. J. Grabau. 2009. No-till organic corn production. American Society of Agronomy National meeting abstracts, available at www.agronomy.org, verified Jan. 5, 2010.

Frey, J., A. Suarez, and L. J. Grabau. 2009. Weed control in no-till organic soybean. American Society of Agronomy National meeting abstracts, available at www.agronomy.org, verified Jan. 5, 2010.

McMaine, J., A. Suarez, and L. J. Grabau. 2009. Bokashi as an organic fertilizer alternative for winter wheat. American Society of Agronomy National meeting abstracts, available at www.agronomy.org, verified Jan. 5, 2010.