Should Roundup Ready soybeans be managed differently than conventional soybeans?

03/23/04

Research in Agronomy Journal suggests producers reduce seeding rates when planting Roundup Ready varieties



Cover: Seeds of white lupin produced in Virginia. See "White Lupin Performance and Nutritional Value as Affected by Planting Date and Row Spacing," by Bhardwaj et al., p. 580-583. Photo by WIlliam H. Porter III.

MADISON, WI, MARCH 23, 2004 -- Roundup Ready soybean acreage has drastically increased since their introduction in 1996. Approximately 84% of Wisconsin soybeans were planted to Roundup Ready in 2003 with similar trends cross the United States. While much research had been conducted with management of conventional soybeans, little had been conducted to see how Roundup Ready soybeans compare.

The study of the effect of adjusting management practices when using Roundup Ready soybean is published in the March-April issue of Agronomy Journal, published by the American Society of Agronomy. Authors are Michael Bertram, University of Wisconsin-Madison and Palle Pedersen, Iowa State University. The research was conducted under the direction of Dr. Edward Oplinger and was supported by the Wisconsin Soybean Marketing Board and Hatch Project 1890.

Soybeans have traditionally been grown in wide rows, but many producers in the northern Midwest plant in narrow rows to reduce disease severity and to increase yield. The research was conducted to test conventional and Roundup Ready soybean varieties from 1997 to 1999 at two locations in the southern, central, and the northern part of Wisconsin. These varieties were grown at three row spacings and three plant populations for each row spacing. Conventional varieties were grown with conventional herbicides while Roundup Ready varieties were grown with both conventional herbicides and Roundup.

Planting soybean in narrow (7.5 inches) or intermediate rows (15 inches) resulted in greater yield than wide rows (30 inches). Yields were similar with narrow rows and intermediate rows, suggesting this may be an alternative for producers with disease concerns.

In general, soybean yield increased when populations were raised from low to optimum, but did not increase from optimum to high. This would suggest that current seeding rate recommendations are adequate and similar for both conventional and Roundup Ready soybeans. However, Roundup Ready soybean yield was similar regardless of plant population in northern Wisconsin.

"The results indicate that management practices when using Roundup Ready varieties should be similar to conventional cultivars. However, when using Roundup Ready soybeans, it may be economically feasible to reduce seeding rates in parts of Wisconsin, as the results from northern Wisconsin demonstrated," says Bertram.

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