1. Soybean Yield, Management and Physiology: Comparison To Corn North Central Branch, ASA March 16-17, 2005 Emerson D. Nafziger Crop Sciences University of Illinois Emerson D. Nafziger Crop Sciences University of Illinois

2. Outline for Today Current status of soybean yields Yield physiology Weather interactions Management issues Summary and “proposal” Current status of soybean yields Yield physiology Weather interactions Management issues Summary and “proposal”

10. Corn and Soybean Acreage in Illinois, 1990-2004

11. For Soybean Yield, How High is “High”? R. Cooper (in IL and OH) reported over 100 bu in sub- irrigated semi-dwarf types 300K seeds/acre in 7-in rows The reported world record (Ray Rawson) is 118 in MI 100+ bu/acre in county strip test in NW Illinois in 1990 on a “virgin” field Highest county average yield was 57 bu/acre in 1998 in JoDaviess County and in 2002 and 2004 in Carroll County, both in NW Illinois Highest yield in the UI variety trials was 82 bu/acre at Perry in 2004 Highest Illinois state avg yield is 50.5 (2004) R. Cooper (in IL and OH) reported over 100 bu in sub- irrigated semi-dwarf types 300K seeds/acre in 7-in rows The reported world record (Ray Rawson) is 118 in MI 100+ bu/acre in county strip test in NW Illinois in 1990 on a “virgin” field Highest county average yield was 57 bu/acre in 1998 in JoDaviess County and in 2002 and 2004 in Carroll County, both in NW Illinois Highest yield in the UI variety trials was 82 bu/acre at Perry in 2004 Highest Illinois state avg yield is 50.5 (2004)

12. Why Not Higher Soybean Yields? A partial list, compared to corn: Soybean has ~50 percent higher energy content per lb of seed and 7% heavier bushels than corn It does photorespiration, losing up to 1/3 rd of photosynthesis to this “useless” process It fixes some of its own N It fills rapidly for ~30 days v 45-50 for corn More sensitive to air pollutants(?) A partial list, compared to corn: Soybean has ~50 percent higher energy content per lb of seed and 7% heavier bushels than corn It does photorespiration, losing up to 1/3 rd of photosynthesis to this “useless” process It fixes some of its own N It fills rapidly for ~30 days v 45-50 for corn More sensitive to air pollutants(?)

15. Yield v maturity date, Reg. 3, MG 3 RR, 2004

16. Yield v maturity date, Reg. 3, RR, 2000

17. Soybean Yield Physiology The ability to maintain high photosynthetic rates throughout seed filling stages defines high yield potential Among C3 crops, soybean has relatively high photosynthetic capacity The maximum sustained seed fill rate is ~3 bushels per day This fill rate sustains for ~30 days under normal temps; can be longer if cooler By far the largest reason for decreased Ps causing lower seed fill and yield is inadequate water The ability to maintain high photosynthetic rates throughout seed filling stages defines high yield potential Among C3 crops, soybean has relatively high photosynthetic capacity The maximum sustained seed fill rate is ~3 bushels per day This fill rate sustains for ~30 days under normal temps; can be longer if cooler By far the largest reason for decreased Ps causing lower seed fill and yield is inadequate water

18. A Mystery of Soybean Yield Physiology There is no clear indication whether soybean is “source-limited” (inadequate Ps) or “sink-limited” (not enough places to accept Ps products = sugars) This “confusion” may be of minimal importance as long as breeders can maintain progress, but it’s still of interest in the field There is no clear indication whether soybean is “source-limited” (inadequate Ps) or “sink-limited” (not enough places to accept Ps products = sugars) This “confusion” may be of minimal importance as long as breeders can maintain progress, but it’s still of interest in the field

19. Evidence for Source Limitation Increasing CO 2 in the atmosphere increases yields (SoyFACE & others) Ozone & other pollutants reduce yield Defoliation reduces yield, if it’s severe enough Drought reduces yield, often by reducing seed size Increasing CO 2 in the atmosphere increases yields (SoyFACE & others) Ozone & other pollutants reduce yield Defoliation reduces yield, if it’s severe enough Drought reduces yield, often by reducing seed size

20. Evidence for Sink Limitation Removing some leaves increases Ps rate in remaining leaves Pale green (low chlorophyll) mutants yield more than Ps rates would suggest Leaves accumulate starch during the day; inability to utilize sugar fast enough? Adding N fertilizer (low fixation) fails to increase yields Removing some leaves increases Ps rate in remaining leaves Pale green (low chlorophyll) mutants yield more than Ps rates would suggest Leaves accumulate starch during the day; inability to utilize sugar fast enough? Adding N fertilizer (low fixation) fails to increase yields

21. “Practical” Yield Physiology With exceptions, soybean plants initiate enough seeds for high yields, but may fail to adequately sustain pods or fill seeds due to reduced Ps during critical stages (R5-R6) Canopies and leaves are usually adequate, but root systems often fail to provide enough water to maintain Ps With potential seedfilling rates of 3 bu/day, reductions in Ps for even short stretches in August hurt yields Starting to fill seeds slightly earlier or extending seedfilling slightly longer can increase yields greatly With exceptions, soybean plants initiate enough seeds for high yields, but may fail to adequately sustain pods or fill seeds due to reduced Ps during critical stages (R5-R6) Canopies and leaves are usually adequate, but root systems often fail to provide enough water to maintain Ps With potential seedfilling rates of 3 bu/day, reductions in Ps for even short stretches in August hurt yields Starting to fill seeds slightly earlier or extending seedfilling slightly longer can increase yields greatly

22. Days after flowering 010203040506070 R1 R2 R3R4 R5 R6 R7 R8 Seed Filling Pod Development Flowering Vegetative Growth Soybean Reproductive Development Indeterminate Growth ©Palle Pedersen

23. Seed and Pod Development ©Palle Pedersen R5R6 R8 (all) R7 (1)

31. Soybean management goals: To enable to crop to take full advantage of good weather when it happens To protect the yield of the crop, at least partly, from disastrously low yields when the weather is poor In practical terms, we need to “position” the crop for maximum seedfilling rates To enable to crop to take full advantage of good weather when it happens To protect the yield of the crop, at least partly, from disastrously low yields when the weather is poor In practical terms, we need to “position” the crop for maximum seedfilling rates

32. Planted Apr. 5 Photo May 24

33. Planting Date & Rate ave. 9 No. IL sites, 2001-03, mid-maturity, 4 seeding rates

34. Effect of Planting Date on Maturity and Plant Height (response to day length) Planting Date Maturity Date Plant Height- in. April 11Sept. 1628.9 April 24Sept. 1730.5 May 11Sept. 2231.6 May 29Sept. 2833.2 Monmouth

35. Planting Date and Seeding Rate Data from J. Gander, Pioneer Hi-Bred

36. Planting Date and Seeding Rate University of Illinois

37. Planting Rate and Variety Data from J. Gander, Pioneer Hi-Bred

38. Seeding Rate and Row Spacing E. Adee, University of Illinois

39. Seeding Rate and Row Spacing P. Pedersen, Iowa State Univ.

40. Seeding Rate Economics University of Illinois ↑ Optimum

41. Variety Maturity & Planting Date, 2001-03

44. Planting Management 100,000 plants per acre is enough to maximize yield, if they’re all healthy and evenly distributed Variety, varietal maturity, row spacing, and planting date don’t seem to affect seeding rate/plant population response much Good quality soybean seed responds little if any to seed fungicidal seed treatment or inoculant Planting in the first half of May is appropriate for soybean, with little loss 1-2 weeks on either side of that period 100,000 plants per acre is enough to maximize yield, if they’re all healthy and evenly distributed Variety, varietal maturity, row spacing, and planting date don’t seem to affect seeding rate/plant population response much Good quality soybean seed responds little if any to seed fungicidal seed treatment or inoculant Planting in the first half of May is appropriate for soybean, with little loss 1-2 weeks on either side of that period

48. According to Some… High corn yields are an accomplishment While High soybean yields are an accident High corn yields are an accomplishment While High soybean yields are an accident

49. Now We Know Better! Still, it’s clear that managing soybean within our weather and soils will disappoint sometimes But, the US remains a good place to grow soybeans, and with continued attention to genetics and inputs, we can continue to compete Still, it’s clear that managing soybean within our weather and soils will disappoint sometimes But, the US remains a good place to grow soybeans, and with continued attention to genetics and inputs, we can continue to compete

50. Seedfill Monitoring in Soybean As a pilot in 2005, we are going to take weekly samples of soybean pods from 25-30 plants Dry and thresh to determine seed wt per plant Relate ΔDW to temperature, moisture, and solar radiation during past week Care to join us? ednaf@uiuc.edu As a pilot in 2005, we are going to take weekly samples of soybean pods from 25-30 plants Dry and thresh to determine seed wt per plant Relate ΔDW to temperature, moisture, and solar radiation during past week Care to join us? ednaf@uiuc.edu

51. Thank You