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Issue No. 14, Article 4/June 26, 2009

Soybean Planting Delays Continue

Soybean planting delays continued this week, with statewide progress moving forward only 6% from June 14. The June 21 Crops and Weather report indicated 79% planted, in contrast with 88% by the same date in 2008 and 96% averaged over the last 5 years. Progress was hampered by several thunderstorms and heavy rainfall, while the high temperatures and humidity contributing to those storms have helped growth of planted corn acres. The East Southeast and Southeast reporting districts are farthest behind, with 45% and 64% planted. Several acres in those two regions are in double-crop cropping systems (winter wheat followed by soybean); 98% of the wheat crop is filled, 42% is ripe, and 6% is already harvested. By now, quite a few soybean acres intended to be full-season single crop will be planted at the same time as many double-cropped acres.

If you have both double-crop and single-crop soybean fields to be planted, scout to find the field offering the best planting conditions. Soybeans in the double-crop rotation (following winter wheat) could perhaps be planted even earlier than some single-season fields. Transpiration of water through the leaves of the winter wheat crop will have wicked water out of the ground at faster rates than soil surface evaporation prior to wheat maturity. However, the residue left following wheat harvest may create a dense mat of straw and slow the rate of surface evaporation if rainfall occurs between wheat harvest and soybean planting. These conflicting factors will create situations that are field-specific based on interactions between wheat maturity and harvest with rainfall timing.

As we approach very late single-crop planting, recommendations should start to follow those for double-cropped soybean:

  • Continue to plant a mid- to full-season soybean variety. I would not switch to a variety with an exceptionally early maturity group for your area. When soybeans are planted late, the length of time contributed to vegetative development by the plant is dramatically shortened, while the time for reproductive development is little shortened. The higher temperatures, and more importantly the increasing night length, that will soon start to occur will cause the plants to flower very small and early in development (potentially V2-V3). If you plant an early-maturity variety, it will not have time to grow much stem length, which reduces the available nodes to set flowers and form pods. In addition to fewer pods, the ability to get under the lowest pods with the combine header could be reduced, increasing harvest loss. The trade-off, of course, is the concern for an early frost. So switching to a late-adapted maturity group for your area to offset these changes shouldn't be done either.
  • The narrower the rows the better now. We are at the calendar date where I would suggest not planting soybeans in 30-inch rows if that is at all avoidable. Narrow (7- to 10-inch) rows from a no-till drill will consistently produce the highest yields when soybeans are planted in late June and early July.
  • Seeding rates should also now be adjusted to place 50% to 100% more plants per acre than recommended for soybeans planted in early May. For most growers, this means targeting a final plant stand between 150,000 and 200,000 plants per acre.
  • Timely July and August rainfall and a normal, or preferably later-than-normal, killing frost this fall would also be helpful. I know you can't control these, but with the right weather conditions through summer, good soybean yields could still be achieved.

--Vince M. Davis

Author:
Vince Davis

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