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eturn to table of contents 90 80 A 80.8 A Yield (bu/acre) 70 60 50 B 58.8 75.7 B B B 63.9 61.6 63.9 B 62.6 C 52.8 B 60.2 B 62.6 C 52.2 2013 2014 2015 40 30 Late May Early June Late June Mid July Planting Date D 32.5 Figure 3. Planting date effects by year on soybean yield. 80 70 Oleic Acid (%) 60 50 40 2013 2014 2015 30 Late May Early June Late June Mid July Late May Early June Late June Mid July Pioneer ® Variety P32T80PR Variety X Planting Date Pioneer ® Variety 93Y42 Figure 4. Oleic acid content expressed as a percent of total soybean oil among planting dates and years. While there was an incremental increase in yield with later soybean maturity, there were no significant differences observed when averaged across years and planting dates. Therefore, mean separation was conducted on planting date by year (Figure 3). Yield of the mid-July planting or earlier maturing soybean varieties may have been impacted by Dectes stem borer (Dectes texanus) infestations later in the growing season. There were no significant differences in oleic acid expressed as a percent of total oil among planting dates for the two Plenish high oleic soybean varieties in the study (Figure 4). Oleic acid was maintained between 70 and 80% for both varieties over all planting dates. Average oleic acid content for non-Plenish high oleic soybean varieties was 23.3% (data not shown). MANAGEMENT IMPLICATIONS Growing environment (location and year) had a significant influence on soybean yield potential — average yield in 2014 was significantly lower than 2013 or 2015. Late May plantings had the highest yield in all three years of the trial. There was no difference between early and mid- June plantings, which indicates an opportunity to realize greater soybean yield when planted in a double-crop system. Mid-July plantings had the lowest yield of all planting dates, except for similar yield with late June planting in 2013. There was an incremental increase in yield with later maturing soybean varieties as planting was delayed; however, there was no significant difference in yield among varieties when averaged among planting dates and years (data not shown). It is recommended to plant later maturing soybeans, maturity group IV or greater, after the end of June to avoid late summer heat and drought risks, especially in dryland environments. Oleic acid levels trended slightly lower as planting was delayed; however, 70 to 80% levels were maintained among all planting dates and years, and differences among planting dates were not significant. The earlier maturing Plenish high oleic soybean varieties tested in this trial performed well in late May and June plantings. Newer, later maturing Plenish high oleic soybean varieties are better suited for July planting dates in the Mid-Atlantic Region. ACKNOWLEDGEMENTS Research conducted by R. Kratochvil, J. Draper, J. Street, D. Murphy, M. Sultenfuss, L. Thorne, and M. Islam of the University of Maryland in collaboration with Bill McCollum and Kirk Reese of DuPont Pioneer as a part of the DuPont Pioneer Crop Management Research Awards (CMRA) Program. This program provides funds for agronomic and precision farming studies by university and USDA cooperators throughout North America. The awards extend for up to four years and address crop management information needs of DuPont Pioneer agronomists and customers and Pioneer sales professionals. 140

eturn to table of contents IMPACT OF LATE PLANTING ON SOYBEAN YIELD IN SOUTHERN ILLINOIS by Eric Alinger, Field Agronomist, Kirk Reese, Agronomy Research Manager, Emerson Nafziger, Ph.D., Professor, Department of Crop Sciences, University of Illinois BACKGROUND AND OBJECTIVES • Many growers are sometimes faced with the decision to plant soybeans at very late dates during the growing season. • Yield of late-planted soybeans can be impacted by the shortened growing season, dry soil conditions, or freeze injury. • In 2015, a survey was taken of soybean fields planted from mid-July to mid-August to assess how yield is impacted by very late planting. 40 37.2 A 31.7 B LSD = 1.9 (bu/acre) Yield (bu/acre) 30 20 10 12.9 C 2.6 D 0 July 16-20 July 20-31 Aug 1-9 Aug 10-17 Late planted soybean showing freeze symptoms. STUDY DESCRIPTION • A survey was conducted of 158 soybean locations in southern Illinois planted between July 15 and August 17, 2015. • Grower location, soybean maturity, planting date, planting rate, and grain yield data were collected. • Yield results were analyzed using linear regression on planting date; grouped into planting date ranges for mean separation using Student’s t-test. RESULTS • Yield was significantly different among all planting date ranges (Figure 1). • Yield declined an average of 1.3 bu/acre per day when planted after July 15 (Figure 2). • Soybeans planted in August suffered freeze injury at several locations, which resulted in significantly reduced yield or no yield in some cases. Planting Date Figure 1. Soybean yield grouped by planting date range. Means with different letters were significantly different at P < 0.001. Yield (bu/acre) 60 50 40 30 20 10 0 7/15 7/20 7/25 7/30 8/4 8/9 8/14 8/19 Planting Date y = -1.3097x + 55310 R 2 = 0.7181 Figure 2. Linear regression of soybean yield on planting date among 158 grower fields in southern Illinois, 2015. 141