Download biological nitrogen fixation (bnf) in legumes: importance in

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: [email protected]
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 N2 fixation: 60Kg N ha-1y-1
 SNF: 100 – 360 Kg N ha-1y-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 (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