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  Free living N 2 fixation: 60Kg N ha -1 y -1  SNF: 100 – 360 Kg N ha -1 y -1 = 30 – 80 Kg Fertilizer N ha -1  Pulses: Pea (105kg/ha), chickpea (75kg/ha), Faba bean (110kg/ha) (Various limiting factors)

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

 Pulses (other legumes) prefer to use Nitrogen in mineral forms (NO 3 , NH 4 ) 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

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 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 N 2 -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