BIOLOGICAL NITROGEN FIXATION (BNF) IN LEGUMES: IMPORTANCE IN - - PowerPoint PPT Presentation

BIOLOGICAL NITROGEN FIXATION (BNF) IN LEGUMES: IMPORTANCE IN SUSTAINABLE AGRICULTURE AND FOOD SECURITY

AI Hassen (PhD) ARC-Plant Protection Research

• P. Bag X134, Queenswood

Email: hassena@arc.agric.za

NSTF- Discussion Forum on Pulses and Food Security, 2-3 June 2016, Emperors Palace Convention Centre, Kempton Park

• Nitrogen fixation is an essential process for all organisms
• Biological Nitrogen Fixation (BNF):
• The Nitrogen Cycle in the tropics.
• Protein contents of human and animal foods
• Diets of resource poor communities
• Yield increase and income generation

• Synergistic biological interaction
• Plants: carbon and energy source
• Rhizobia/Bradyrhizobia: fixed nitrogen
• Pulses: Pea (105kg/ha), chickpea (75kg/ha), Faba bean

(110kg/ha) (Various limiting factors)

• Free living N2 fixation: 60Kg N ha-1y-1
• SNF: 100 – 360 Kg N ha-1y-1 = 30 – 80 Kg Fertilizer N ha-1

Schultze and Kondorosi, 1998. Ann Rev Gen; www.cilr.uq.edu.au

• Pulses (other legumes) prefer to use Nitrogen in mineral

forms (NO3, NH4) as this requires less energy than making their N from BNF ( to use ‘N’ from the soil) .

• If it is a question of adding fertilizer ‘N’, BNF is the best

alternative than adding inorganic fertilizer.

• Pulses high nitrogen requirement for protein synthesis
• Need to apply very large quantity of inorganic fertilizer

• Example: to obtain soybean yield of 2000kg ha-1
• Need to apply 600 – 900 Kg Urea ha-1
• 280 – 413 kg Nitrogen
• The same yield ( 2000 kg ha-1 can be obtained by BNF, no

addition of N-fertilizer; BNF is cost effective

• Necessary to inoculate pulses and other legumes with

Rhizobium, symbiotic nitrogen fixing bacteria

• Compete with indigenous rhizobium
• Effective in nodulating the target legume
• Fix atmospheric N with a wide range of host genotypes
• Increase yield to the desired level
• Persist in the soil
• Maintains genetic stability

• ARC-Plant Protection Research Institute
• South African Rhizobium Culture Collection (SARCC)
• Several hundreds of rhizobia (National Assets)
• Long term projects, field collections, client samples and

international institutions

• Rhizobium, Bradyrhizobium, Sinorhizobium, Mesorhizobium
• Routinely maintained (viability, purity, effectiveness)

• About 15 commercial strains of N-fixing bacteria
• Rhizobium sp. TJ14 (Peas)
• B. japonicum strain XS21 (Cow pea, ground nut)
• Rhizobium sp. Strain UD5 (Faba bean & broad beans)
• Bradyrhizobium sp. Strain VK10 (Lupin)
• Bradyrhizobium japonicum WB74 (Soybean)
• Sinorhizobium meliloti RF14 (Lucern)
• Currently Mesorhizobium sp (Rooibos)

• Nodulation occurs during early flowering
• Starts to emerge 14 days after crop emergence
• Nodule numbers and N-fixation maximum during early

to mid flowering

• Many, big size, mainly on the crown, red in color inside

Leghaemoglobin

A B C

• No indigenous strains of the required Rhizobium
• E.g. The case of soybean in South Africa
• Bradyrhizobium japonicum strain WB74

(Australian strain under the name CB1805)

• When the level of indigenous Rhizobium population is

extremely low (10 – 1000 cells/g soil).

• Adding small amount of fertilizer ‘N’ stimulates

nodulation and growth.

• Not always true for some legumes, jeopardizes the

process of nodulation and N- fixation

• Unutilized fertilizer N carried over from previous cereal

crops negatively influences BNF.

• Level of N-fixation commonly low in pulse crops grown

in a rotation with fertilized maize. (Crop rotation??)

• Recommended level of ‘N’ranges 15kg -30 kg/ha

• Biologically fixed ‘N’ bound in the soil OM
• Less susceptible to soil chemical transformations
• Volatilization of N2-oxide (greenhouse gas)
• Leaching of (NO-

3)

• Climate change
• Reduced contamination of water bodies
• Minimizes depletion of non renewable resources

• Pulses, major source of dietary proteins and important

component of subsistence and low input agriculture

• Global climate change posing threat
• Fluctuations in pulse yield and frequent crop failure
• Most pulses susceptible to abiotic & biotic factors
• Acidity, salinity, drought, Reactive Oxygen Species

ABIOTIC STRESS

• More focus be given to pulse BNF research
• Investment in Rhizobium inoculation technology
• Participation by public & private partnership
• Effective BNF dissemination strategy (farmers)
• Capacity building along BNF value chain
• Partnership with research and academic institutions

in the developed nations