Biological Nitrogen Fixation Management Program

Discuss edaphic, climatic and biotic factors limiting biological nitrogen fixation.3.

Figure 9. The various Factors that control nitrogen fixation.

The other limiting biotic factors could be:

excessive defoliation of host plant,
crop competition, and
insects and nematodes
Inoculation of LegumesIf specific and effective rhizobia are absent in a soil, or if they are present in low numbers, it is necessary to introduce the rhizobia in that soil to ensure proper nodulation and nitrogen fixation.

Any stress that reduces plant activity will reduce nitrogen fixation.

For example, Azospirillum species have been shown to fix nitrogen when growing in the root zone (rhizosphere) or tropical grasses, and even of maize plants in field conditions.

Lamb, J.F.S., D.K. Barnes, M.P. Russelle, C.P. Vance, G.H. Heichel, and K.I. Henjum. 1995. Ineffectively and effectively nodulated alfalfas demonstrate biological nitrogen fixation continues with high nitrogen fertilization. Crop Science, 35, 153–157.


in relation to the fixation of nitrogen

The occurrence of the symbiotic relationship is heavily dependent upon a variety of soil conditions. If your program incorporates nitrogen fixation, the following considerations can determine your success.

Symbiotic Nitrogen Fixation Technology.

The figure below gives examples of some common cross-inoculation groups that may assist you in selecting the proper rhizobial inoculant for a particular legume host. The proper combination of rhizobia and legume will result in the optimal nodulation and most nitrogen fixation. From this figure, we see that using soybean rhizobia with a soybean plant forms an effective symbiosis, while using a soybean rhizobia with a leucaena plant does not. However, cowpea rhizobia is capable of nodulating both mungbean and peanut.


Figure 8. Specificity of Rhizobia for successful nodulation of certain legumes.

Biological nitrogen fixation in forage and livestock systems.

But the major conversion of N2 into ammonia, and thence into proteins, is achieved by microorganisms in the process called nitrogen fixation (or dinitrogen fixation).

Dinitrogen fixation by plantassociationsexcludingle-gumes.

Legumes and Rhizobia are not the only species that can establish a mutual symbiotic relationship needed for nitrogen fixation to oocur.

In A treatise on dinitrogen fixation, R.

At the time of pod fill,nodules on annual legumes generally lose their ability to fix nitrogen because theplant feeds the developing seed rather than the nodule.

Energy used for nitrogen fixation cannot be used in repro-duction.

Nitrogen fertilizer isapplied at planting to these legumes when grown on sandy or low organic matter soilsto supply nitrogen to the plant before nitrogen fixation starts.