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The Ability of Legumes

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Posted Sep. 30, 1997

The ability of legumes to fix nitrogen has long been a fascination to forage producers. The nitrogen released from nodules benefits plants and increases forage production. Due to the hot and dry summers we have, annual legumes perform best in the Ardmore area. The environment is too harsh for most perennial legumes to persist in grazing systems.

The application of high rates of nitrogen(N) to bermudagrass has a negative effect on legumes that are present. N applications stimulate dense stands of very competitive, efficient bermudagrass. When N rates exceed 100 pounds per acre of actual nitrogen, the density and competitiveness of the bermudagrass offers little opportunity for annual plants to grow.

For the intensive bermudagrass manager proper fertilization and grazing reduces weed problems. While reducing weeds, the opportunity for annual legumes to establish can also be reduced. To have consistent stands of annual legumes, certain conditions must exist:

  1. Good soil seed contact.
  2. Good water and light availability for seedlings.
  3. Soil reaction between pH 6.0 and 7.0.
  4. Adequate levels of phosphorus and potassium.
  5. Deferment of livestock grazing during establishment.

Vigorous bermudagrass and annual legume establishment is an oxymoron. Highly productive bermudagrass systems are not the place for legumes. Sometimes at lower stocking and N rates, annual legumes may be a significant part of the forage production system. Where climatic conditions are favorable, perennial legumes are more likely to persist in bermudagrass; thus, perennial mixtures become more practical.

Don't confuse the two systems. They have different management and production potentials. Bermudagrass can efficiently utilize several hundred pounds of actual N per acre. If legumes are desired, N rates must be limited. Then they can express themselves and generate up to 100 pounds of actual N per acre.

There can be tremendous differences in the amount of forage produced from the two systems. We would expect about 2 tons of forage per acre from legumes producing 100 pounds of N per acre. Whereas, six to eight tons of forage per acre would be anticipated when 3-400 pounds of actual N per acre is applied.

Both systems are practical. The high rates of N fertilizer have the potential to generate the largest gross returns per acre. To analyze your situation, ask an economist to assist you in compiling your costs and returns. See which production technique will best accomplish your goals. Neither system is without risk and both need management. Please, contact me or other agronomists for further discussion if you have questions.