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ARS Home » Southeast Area » Stoneville, Mississippi » Crop Genetics Research » Research » Publications at this Location » Publication #136344
Title: INFLUENCE OF EARLY-SEASEON NITROGEN AND WEED MANAGEMENT ON IRRIGATED AND NONIRRIGATED GLYPHOSATE-RESISTANT AND SUSCEPTIBLE SOYBEAN.

Author
item Heatherly, Larry
item SPURLOCK, STAN - MISS. STATE UNIV.
item REDDY, KRISHNA - USDA-ARS

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2002
Publication Date: 4/1/2003
Citation: HEATHERLY, L.G., SPURLOCK, S.R., REDDY, K.N. 2003. INFLUENCE OF EARLY-SEASEON NITROGEN AND WEED MANAGEMENT ON IRRIGATED AND NONIRRIGATED GLYPHOSATE-RESISTANT AND SUSCEPTIBLE SOYBEAN.. AGRONOMY JOURNAL. Vol. 95:446-453.

Interpretive Summary: Low profits are common from soybean plantings in the midsouthern US. This is a result of high input costs associated with frequent low yields. Weed management costs can be manipulated by using either conventional cultivars with non-glyphosate herbicides or glyphosate-resistant cultivars with glyphosate. Other costs can be controlled by using only those inputs (such as fertilizers) that will result in a higher net return. In a non-irrigated or low-yield environment, use of glyphosate-resistant soybean cultivars and glyphosate resulted in a less negative net return than using conventional cultivars with non-glyphosate herbicides. In an irrigated or high yield environment, using conventional vs. glyphosate-resistant cultivars resulted in greater profit. Use of postemergent-only weed management vs. preemergent followed by postemergent weed management was as effective in controlling weeds, and resulted in higher net returns with glyphosate-resistant cultivars. Adding 30 lb. nitrogen per acre in the early growing season did not affect yield of either conventional or glyphosate-resistant cultivars, and resulted in lower net returns. These results will allow producers to decide on the best weed management system for soybean grown in nonirrigated and irrigated environments when using conventional and glyphosate-resistant soybean cultivars in the midsouthern US, and to forego the $15 to $20/acre cost associated with use of added nitrogen as an input.

Technical Abstract: Field studies were conducted from 1999 through 2001 on Sharkey clay at Stoneville, MS (lat. 33 26'N). The objective was to determine the effect of 35 kg N ha-1 applied early in the growing season to conventional (CONV) and glyphosate-resistant (GR) soybean cultivars grown under two weed management systems with irrigation (I) and without irrigation (NI). Weed management systems were: 1) preemergent (PRE) followed by postemergent (POST) non-glyphosate broadleaf and grass weed management (PRE + POST) applied to both CONV and GR cultivars; and 2) POST broadleaf and grass weed management (POST) using non-glyphosate herbicides on CONV cultivars and glyphosate on GR cultivars. Under the conditions of this study, use of GR vs. CONV cultivars in the NI or low-yield environment resulted in slightly higher yield, but all net returns were negative. In the I or high-yield environment, use of CONV vs. GR cultivars usually resulted in greater yield and profit only when PRE + POST was used. Use of PRE + POST compared to using only POST weed management was not necessary for achieving highest yield or net return with either CONV or GR cultivars. Nitrogen applied early in the season had no effect on weed management in or soybean yield from either CONV or GR cultivars, and lowered net return.