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Agronomy Day 2008

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Tour A

Pushing Soybean Yields

Emerson D. Nafziger
Emerson D. Nafziger
Department of Crop Sciences

In 2007, Kip Cullers of southwestern Missouri grew irrigated soybeans that yielded 154 bushel per acre. While yield records for soybean have gotten less attention than those for corn, there is no doubt that this is the highest yield ever recorded for soybean. I visited Mr. Cullers in August 2007 to observe his crop and to discuss with him his practices. Here are some things that he mentioned:

  • He is primarily a vegetable (green beans) grower, and first produced soybean in 2006. His soybean contest area in both 2006 and 2007 were fields where soybean had never before been grown. Unless he unexpectedly changes fields, his 2008 and subsequent “contest” soybeans will be in the same field where soybean grew before (after a year of corn), meaning that any “first time ever in the field” soybean advantage will be lost.
  • He uses a considerable amount of poultry litter in the fall, before thoroughly tilling the cornstalks from the previous crop. He uses some N through the irrigation system as well, but amounts are not known. He mentioned using a “stalk breakdown aid” that contains microbes, sugar, and N. Soybeans did have nodules, though number and activity were not assessed.
  • A number of products are applied to the crop, including fungicides, micronutrient mixtures, etc.
  • Water is applied frequently; Mr. Cullers said that he was applying 1/3rd of an inch per day in the morning, and that he runs the system again fast (at a lower water rate) in the afternoon to cool the canopy. Yields in that part of Missouri are generally below the state average. Irrigation is clearly the major reason for the high yields; Mr. Cullers says that he needs high amount and frequency of irrigation water to get flowers to form pods in green beans, and that he takes this same approach for soybeans.
  • He plants soybean with a Monosem twin-row (7.5+22.5” rows) planter using a seeding rate of about 300,000 per acre, or about 9 seed per foot of individual rows. He reported that stands were about 250,000 plants per acre.
  • He uses Pioneer® soybean seed, of late Maturity Group 4 maturity. This is typical for the area.
  • Plants were lodged somewhat in early August, and Mr. Cullers mentioned wanting to find a way to reduce plant height and to keep plants from lodging.

A group from the Agronomy Department of Iowa State University visited Mr. Cullers’ field in September, and in general they confirmed that the plants had very large numbers of pods, and that beans were filled out to at least normal size. The following photo taken during their visit was provided by Dr. Palle Pedersen.

At this stop we can see a first attempt at reproducing some of what Kip Cullers has been doing, in hopes of seeing how high yields will go, and also of seeing what if anything some of these practices contribute to yield. Treatments include irrigated versus unirrigated, untreated seed versus seed treated with Optimize® and Cruiser Maxx®, and combinations of N and micronutrients, as well as an experimental growth regulator that shortens stems. This research is funded by a special grant from the Illinois Soybean Association, whose support we acknowledge with great appreciation.

What does it take, in terms of plant and seed numbers, to produce high soybean yields? As an example, 100 bushels per acre at 2,800 seeds per lb means 16.8 million seeds per acre. At 200,000 plants per acre, this is 84 seeds per plant or 30 pods per plant if pods have an average of 2.8 seeds each. These numbers don’t seem too far out of the ordinary, but the fact that we often end up with yields of 40 to 60 bushels per acre tell us that it’s difficult to get all plants to perform up to the average. It’s clear that without enough pods and seeds, there is little chance for high yield. Will irrigation and other inputs help increase seed number and then to help these seeds to fill to normal size? Stay tuned.

Energizing Agriculture