Phaseolus coccineus is used as green manure or cover crop and is specifically suitable for high altitude, low fertile, high Al or salt containing soils under moisture stress. Close relationship of Phaseolus coccineus with Phaseolus vulgaris, Phaseolus dumosus Macfad. (Phaseolus polyanthus),  Phaseolus costaricensis Freytag and Debouck. had been reported. The amount of nitrogen fixed by Phaseolus vulgaris is lesser than other pulses such as groundnut, soya bean, cowpea etc. and estimated at about 125 kg/ha [Brink, M. And Belay, G. (Eds) Plant Resources of Tropical Africa 1. Cereals and Pulses, Prota Foundation, Wageningen, Netherlands/Backhuys Publishers, Leiden, Netherlands, 2006. P 148] .

The amount of nitrogen fixed by interspecific crosses with introgression from Phaseolus coccineus had been reported.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4998141/pdf/main.pdf

Going through the following link may provide further clue to the answer of the question:

http://link.springer.com/article/10.1007/BF02374821

Phaseolus coccineus fixes 50 Kg. of nitrogen per hectare per year.

 Biological nitrogen fixation can take many forms in nature, including blue-green algae (a bacterium), lichens, and free-living soil bacteria. These types of nitrogen fixation contribute significant quantities of NH3 to natural ecosystems but not to most cropping systems, with the exception of paddy rice. Their contributions are less than 5 lb of nitrogen per acre per year. However, nitrogen fixation by legumes can be in the range of 25–75 lb of nitrogen per acre per year in a natural ecosystem, and several hundred pounds in a cropping system (Frankow-Lindberg and Dahlin, 2013; Guldan et al., 1996; Burton, 1972).

Please see following publication for details:

http://aces.nmsu.edu/pubs/_a/A129/

Dear Suresh Malhotra, I think the assertion than cropping systems can or do not have ability to satisfy the cropping N requirements of competitive crop systems in a misnomer. If we have a Nitrogen demanding crop like maize or rice the use of legume cover crop or green manure can provide all the Nitrogen for top yields. In addition the yield of maize following a soybean crop for instance will produce about 18% higher crop yield based on rotation effect. When legume crop are used in hay forage mixture they not only reduce the Nitrogen required as amendment but also improve the Carbon content in soil rejuvenating the soil structure and biology in addition. When legumes are added to grass pastures the earthworm populations skyrocket 3 to 4 times the grass monoculture. Interestingly work in Australia has shown than when termites are restricted within two years up to 80 to 90% of the soil Nitrogen level is lost. The symbiotic microbial communities in the termite gut are very active sites of Nitrogen fixation. Recently in Guinea West Africa I witnessed the abundant prairie production and health where termite mounds were abundant at the concentrations of the termites I observed the rates of Biological Nitrogen fixation would be estimated at 300 to 400 kgN/ha/year enough for top tier grass production. The Nitrogen fixation concentrated on legumes is also not exhaustive as symbiotic Azolla in rice paddy can provide the total Nitrogen need for top rice production. This idea that Nitrogen in biological fixed forms is also being limited is being challenged by the association of Nitrogen fixing rhizobacterial in tropical grass in work done in Brazil. As a past research Director for Rodale Institute Farming System Trial showed through legume based cover cropping and rotation can produce all the cropping systems Nitrogen needs and increase crop yields while improving critical soil organic matter. The application of effective methodologies to do this are available but often the application has lagged from lack of knowledge desire and aptitude. 

Yes Dr Paul You are right and have detailed about many related aspects. Compliments to you for good response that legume based cover cropping and rotation can produce all the cropping systems Nitrogen needs and increase crop yields while improving critical soil organic matter. But what we need is application of effective methodologies  and lagged from lack of knowledge desire and aptitude. 

All well and good but let's get back to the question at hand. I have no doubts that nitrogen fixing cover crops can improve soil: https://www.youtube.com/watch?v=_ERXyjX0rHI

I'm looking for a very specific set of information an average rate of nitrogen fixation per hectare, to which there are 2 plausible answers 125 kg per acre and 50 kg per acre but no reference listed. Arvind where is the reference?

Given the prodigious amount of cover this crop can produce it seems a bit odd to me that no one had the wherewithal to record how much dry-matter per hectare it produces.

Though the grain yield had been reported, resources reporting the per hectare dry matter production of Phaseolus coccineus are not available. The following sources reported per square metre dry matter production:

http://scialert.net/qredirect.php?doi=ijar.2009.270.278&linkid=pdf

https://naldc.nal.usda.gov/naldc/download.xhtml?id=IND43759296&content=PDF

The following links may also be explored:

http://www.sciencedirect.com/science/article/pii/S0304423812005833

http://news.ari.gov.cy/publications/mr43-hadjichristodoulou.pdf

Thank you Nilay Borah!  

Good response to question Mr. Justin. You are looking for dry matter production per hectare. But literature available is meagre.

@ Paul, Excellent answer explaining the benefits of including legumes in cropping systems and their contribution to the long-term productivity and sustainability of agricultural systems by N fixation and other ‘rotation-effects’.

I agree, except for one point on the termites.  I have seen several references on the relationship between ‘termite infestation’ and ‘pasture degradation’ in Brazil.  Please see the references below for examples:

De Lima et al. (2011) Relationship between the presence of termite mounds and pasture degradation.

http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-204X2011001200016

Merten and Minella (2013) The expansion of Brazilian agriculture: Soil erosion scenarios. http://www.sciencedirect.com/science/article/pii/S2095633915300290

These and other Brazilian literature indicate that termite infestations and pasture degradation has some connection. I am not sure about the cause and effect relationship between the two (which one occurs first): ‘pasture degradation’ or ‘termite infestation’?  Pictures in the second publication above are impressive.

@ Justin, I am sorry taking the discussion in another direction, but relating to Phaseolus coccineus L., I have found this paper that provides data related to dry grain yield.  May be useful to you.

Stefan et al (2013) Seed inoculation with plant growth promoting rhizobacteria enhances photosynthesis and yield of runner bean (Phaseolus coccineus L.)

http://www.sciencedirect.com/science/article/pii/S0304423812005833

Regards.

Susantha.