AGRONOMIC NEWS ITEMS
From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335
Summer 1998, No. 8
DON'T LET NUTRITION LIMIT SOYBEAN YIELDS
Soybeans require high levels of available nutrients from planting to harvest. Adequate fertility will not guarantee top profit soybeans, but top profit yields cannot be obtained without these vital inputs. The soybean plant, just like a factory, requires a minimum level of raw materials to generate grain as the finished product. The goal is to supply the amounts needed and on a schedule tuned to soybean plant and seed development.
Stimulate rapid seedling development. How? Auburn scientists used starter fertilizer (45 pounds per acre nitrogen) to boost grain yield. For the determinate variety, Cook, starter boosted seed yield (from 32 to 37 bushels per acre), vegetative growth, plant height and the nitrogen content in plant tissue. Phosphorus and potassium can be included with band placed starter nitrogen.
Up-front feeding benefits soybeans. Fertilizing wheat for both crops should work...and it does much of the time. However, several conditions exist which increase soybean response to split applications and late season fertilization.
Direct soybean fertilization deserves consideration. An Illinois consulting firm's research tells why. The same reasons hold true for the Southeast.
- Fertilizer nutrients applied to wheat can be temporarily tied up in straw residue and microbes unavailable to soybean seedlings.
- Fertilizer placed for best wheat use is not likely to be in the right place for easy access by soybean seedling roots. Fertilizer placed about two inches to the side and below the seed is usually best for seedling growth.
- Availability of phosphorus to next crop soybeans will decline with time due to being changed into less available forms by soil constituents.
- On sandy soils the heavy rains last fall and this spring have leached some potassium, magnesium, sulfur, and boron out of the plant root zone. Also, when soybean fertilizer is applied to wheat, nearly eight months will pass before soybeans are planted and seedlings have a chance to use it.
Program soybean fertilization to supply crop needs throughout the growing season. The period of greatest potassium uptake is during the 15 days between full bloom and early pod fill. For phosphorus, uptake intensifies from full bloom to seed maturity. For some soils, fertilizer applied to wheat can do the job. For many sandy Coastal Plain soils, high yield, high profit soybeans will likely respond best to a well fertilized wheat crop plus fertilizer directly applied to the soybeans.
- Nutrient availability will be highest when fertilizer is applied just prior to soybean needs.
- Small grains and soybeans have different nutrient requirements and grow under different soil conditions.
- A good small grain crop can take up more nutrients than expected, leaving soybeans short of nutrients.
For more information, contact Dr. Noble R. Usherwood, Southeast Director, PPI, 655 Engineering Drive, Suite 110, Norcross, GA 30092-2837. Phone (770) 825-8070.
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