RA 00110.pdf - OAR@ICRISAT

Pearl Millet Microbiology
Potential of Associative Nitrogen Fixation in Rainfed Cereals
(Potentiel de la fixation de l'azote par l'association racine-microbes chez les cereals
pluviales)
P. Tauro
Professor & Head, Department of Microbiology, Haryana Agricultural University, Hisar, Haryana 12S 004,
India
Association between cereal plant roots and nitrogen-fixing bacteria has been well documented. Seed treatment
with bacteria such as Azospirillum has shown to be beneficial. The mechanism by which cereals derive
benefits from such association is, however, not very clear. In India, over 70% of the cropped area is rainfed
agriculture, with little or no nitrogen inputs, so yields are low and variable. Pearl millet is grown on sandy soils,
generally in rotation with chickpea. Average grain yields range between 200-300 kg ha -1 in Rajasthan, and
between 500-600 kg ha -1 in Haryana, with about twice as much straw as grain. Recovered nitrogen under these
conditions is 5-20 kg ha -1 . Any contribution from associative nitrogen fixation, however small, would have a
greater meaning in this system than in irrigated cereals.
Our studies over the past few years have revealed varying levels of nitrogenase activity which differ with
genotypes. Marginal yield increases have also been reported from seed treatment with bacteria.
Factors Affecting Nitrogen Fixation Associated with Cereals
(Facteurs influencant la fixation de l'azote chez les cereales)
S.P. Wani
Microbiologist, Cereals, 1CRISAT, Patancheru, Andhra Pradesh 502 324, India.
Nitrogen fixation is the result of interaction between the host plant, nitrogen fixing bacteria, and the
environment. Nitrogen fixation associated with cereals may be improved by manipulating factors that affect
the process either individually or in combination. Genotypic variation for stimulating nitrogen fixation has
been observed in lines or cultivars of sorghum, pearl millet, and minor millets. Large variability from plant to
plant in nitrogenase activity has been observed in the Ex-Bornu population of pearl millet. Work is underway
to stabilize high and low nitrogenase activity in this population.
Diurnal variation in nitrogenase activity of plants grown in field or greenhouse was observed. The highest
level of activity occurred toward the end of the photoperiod. However, such a variation was not observed with
plants placed under a constant temperature in the glasshouse. Seasonal variation in nitrogenase activity of
plants was also observed and coincided with the biomass development of the plant. Both were highest at
flowering.
Environmental factors such as temperature, radiation, soil moisture, oxygen partial pressure, and soil
factors (e.g., combined N and organic carbon levels) are known to affect nitrogen fixation. Significantly higher
nitrogenase activity and better growth of sorghum and millet plants occurred when plants were grown in a
mixture of sand and farmyard manure ( F Y M ) than when grown in vermiculite, soil, or a sand and soil
medium. Nitrogenase activity and plant growth were greater in a mixture of sand with 2 or 3% F Y M than with
0.5 or 1% F Y M . Activity was higher when the plants were incubated at 33°C or 40°C than at 27°C. Activity
also increased with increasing soil moisture. Nitrogenase activity in sorghum plants grown in tubes filled with
washed sand was drastically reduced when the plants were regularly fed with a solution of combined nitrogen
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