Weed Management Systems for Conventional and Glyphosate‐Resistant Soybean with and without Irrigation

Abstract

almost always made before the onset of drought and without knowledge of ensuing moisture status for subse-Management inputs that maximize economic return from the early quent crop and weed development. This presents a chalsoybean [Glycine max (L.) Merr.] production system have not been evaluated fully. The objective was to determine the effect of weed man-lenge, especially in NI production systems that often agement on yield and net return from early planted maturity group result in low yield in the midsouthern USA. (MG) IV and MG V glyphosate [N-(phosphonomethyl)-glycine]-resis-A majority of the soybean hectarage in the midsouthtant (GR) and conventional (CONV) soybean cultivars grown in the ern USA is NI even though past research has shown early soybean production system with (IRR) and without (NI) irrigathat yield and net return will increase from irrigation tion. Field studies were conducted from 1996 through 1999 on Sharkey (Heatherly, 1999a). The small profit margin and large clay (very-fine, smectitic, thermic Chromic Epiaquert) at Stoneville, start-up costs associated with land leveling to accommo-MS (33؇26 N lat). Weed management systems were (i) pre-emergent date furrow or flood irrigation, or the initial purchase (PRE) broadleaf followed by postemergent (POST) broadleaf and cost associated with overhead irrigation systems, can grass weed management (PRE ϩ POST) and (ii) POST broadleaf make capitalization of irrigation capability prohibitive. and grass weed management (POST). Use of POST-only weed management was cheaper, yielded more, and resulted in greater net returns Thus, most land used for soybean production in the than did use of PRE ϩ POST weed management with both CONV midsouthern USA presently is committed to either an and GR cultivars. Under the conditions of this study, use of GR vs. IRR (start-up costs absorbed in past) or NI production CONV cultivars in an NI or low-yield environment resulted in greater system. Management of NI and IRR plantings of soyprofit ($52 vs. Ϫ$17 ha Ϫ1 3-yr average, respectively). Use of CONV vs. bean in the midsouthern USA entails different sets of GR cultivars resulted in greater profit in an IRR or high yield environproduction practices, especially for weed management ment ($382 vs. $266 ha Ϫ1 3-yr average, respectively). These results (Heatherly et al., 2002), because the opportunity for indicate that use of GR cultivars with POST-only weed management profit is different between the two systems (Heatherly will result in greater profit in an NI environment while use of CONV and Spurlock, 1999). cultivars with POST-only weed management will result in greater Many weed management systems (WMSs) provide profit in an IRR environment.is a nonselective herbicide that kills both annual and

A Meta-Analysis for the Impact of Transgenic Crop Adoption on Corn and Soybean Yield

“…When infestation levels of insects and weeds are high, TCs would provide higher yield compared to the conventional varieties. These trends were observed by other field studies (Bertram and Pedersen, 2004;Bruns and Abbas, 2006;Dillehay et al, 2004;Heatherly et al, 2002;Heatherly et al, 2003;Lauer and Wedberg, 1999;Mungai et al, 2005;Shaw et al, 2001;Singer et al, 2000;Stanger and Lauer, 2006).…”

“…In the early adoption stage of TCs, transgenic crops with IR traits usually yielded similar to near-isolines (Baute et al, 2002;Cox and Cherney, 2001;Dillehay et al, 2004;Traore et al, 2000), suggesting that the insertion of an IR gene in the early IR crops did not provide higher yield. However, some of the first transgenic crops with GR traits provide the same or even lower yield on average than conventional varieties due to the introduction of the GR gene into varieties with lower yield potential (Elmore et al, 2001;Heatherly et al, 2002 andLoecker et al, 2010;Shaw et al, 2001). However, transgenic traits were later introduced into improved potential yield varieties and generally showed that transgenic hybrids produced similar or higher yields than conventional varieties.…”

“…For instance, Bertram and Pedersen (2004) found that no yield difference between transgenic and conventional soybean variety was observed in LYE caused by cool weather conditions, but transgenic soybean averaged 6% less yield than conventional varieties in normal temperature conditions. A field study also showed that GR soybean produced greater yield and net returns in LYE by drought stress, but conventional varieties generally produced greater yield and net return than transgenic soybeans in irrigated environment (Heatherly et al, 2002;Heatherly et al, 2003). The results are speculated that current conventional varieties have been bred to have high yield potentials under low to moderate infestation because of their great tolerance to infestation damage.…”

“…Soybean yield comparisons between GR hybrids and conventional varieties have also shown that soybean yield were dependent on growing conditions (Bertram and Pedersen, 2004;Elmore et al, 2001;Fernandez-Cornejo et al, 2002;Heatherly et al, 2002;Heatherly et al, 2003;Shaw et al, 2001). For instance, Bertram and Pedersen (2004) found that no yield difference between transgenic and conventional soybean variety was observed in LYE caused by cool weather conditions, but transgenic soybean averaged 6% less yield than conventional varieties in normal temperature conditions.…”

Influence of Early-Season Nitrogen and Weed Management on Irrigated and Nonirrigated Glyphosate-Resistant and Susceptible Soybean

“…Weed management systems were (i) pre-emergent fol-Cost of weed control using a postemergence managelowed by postemergent weed management using nonglyphosate herbiment program for GR cultivars should be less, even cides applied to both GR and non-GR cultivars (PRE ϩ POST) andwith the greater cost for seed of most GR cultivars (ii) postemergent weed management using glyphosate on GR cultivars (Reddy et al, 1999;Heatherly et al, 2002b). cultiflexibility to control a broad spectrum of weeds in soyvars using two weed management systems in irrigated and nonirrigated bean with no concern for crop safety (Reddy, 2001).…”