Biofertilizers for rice cultivation
BIO-FERTILIZERS ARE eco friendly and are environmentally safe.
They form not only part of integrated nutrientsbut are of low cost
which is of immense help to the farming community. Biofertilizers
are widely used in riceproduction. The biofertilizers used for rice
crop are Azospirillum, Phosphobacteria, Blue green algae azolla
andMycorhiza.
Methods of application of biofertilizers and their usage are
discussed below.
Azospirillum: is a symbiotic bacteria and it is an important
biofertilizers used in rice. Azospirillum treatment isrecommended
for seed, seedlings and in main field.
Seed treatment: 600 glha of Azospirillum culture are to be mixed
with water where the seeds are soaked one nightbefore sowing in the
nursery bed.
Seedling heatment: A slurry can be prepared by mixing
Azospirillum at 1000 glha in 40 litres of water and rootportion of
transplanted rice seedlings are dipped in bacterial suspension for
15-30 minutes and then they aretransplanted.
Main field: 2000 glha of Azospirillum with 25 kg farmyard mamure
and 25 kg of soil are mixed uniformly andbroadcasted in the main
field before transplanting.
Uses:
- Azospirillum bacteria thrives in root zones of rice and is
capable of fixing more atmospheric nitrogen which isabsorbed by the
plants. Root exudates of the crops provide nutrients for survival
and multiplication of the bacteria.
- Azospirillum also solubilizes phosphorus and silicon to some
extent required by rice.
- It renders plant drought tolerant when irrigation or rainfall
is delayed.
- By adopting Azospirillum application 30 per cent of the
inorganic nitrogen usage can be reduced.
Blue Green Algae (BGA) is another type of biofertilizer used as
an alga form. Important species are Cyanobacteria,Anabaena, Nostoc
and Tolypothrix. Blue green algal occurs naturally and comes up
well under moist conditions.This can also be artifially
cultured.
Beds of size 20 x 2 m are prepared in a ploughed land bunded on
all sides and water is let into the field to a heightof 10 cm and
maintained for 2-5 cm depth. 5 kg of Algal inoculum with 100g of
lime are sprinkled for one cent plot.
Ater 30 days, without drainage of water, plot is dried and hence
algal mat settles over the soil. Drying peel of likeflakes is
collected and distributed for rice field application at the rate of
10 Kg/ha, 10 days after transplanting.
Otherwise, algal flakes can be powdered, mixed with 25 kg of
farmyard manure and 25 kg of soil and can bebroadcasted. At the
time of application, a thin film of water is to be maintained.
Uses:
- The nitrogen fixed by BGA is about 15 kg/ha over a season.
- BGA elaborates vitamin Biz and growth factors that makes the
plant grow vigorously.
- It oxygenates the water impounded in the field.
- It excretes organic acids that renders phosphorus
solubilisation.
- The algal mat in paddy fields also protects loss of moisture
from the soil.
Azolla is a water fern having an algal symbiont Anabaena azolla
fixing atmospheric nitrogen.
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Azolla can be multiplied by constructing nurseries with 10 cm
deep standing water and adding superhphosphate at8 kg P2o5/ha in
small plots. Inoculation can be done at 8 kg/sq.m. Azolla can be
used immediately after harvest.
It can be applied as green manure prior to rice planting or can
be grown as dual crop with rice. About 10 tonnes offresh Azolla per
hectare is equivalent to 30 kgN/ha.
Uses:
- Azolla excretes organic nitrogen in water during its growth
and also immediately upon trampling.
-Fern fronds are soft and rapidly decomposed.
-It absorbs traces of potassium from irrigation water.
-Azolla provides nitrogen, potassium organic carbon etc.
-It prevents weed growth in rice field water.
Phosphobacteria: This type of biofertilizers solubilise
phosphates in the soil and render them in available form forcrop
plants. It can be applied for low land and upland rice.
This is applied as the same dose in same manner as Azospirillum.
Bacteria like Bacillus megatherium varphosphaticum, pseudomonas,
fluorscens, fungi like Pencillium digitatum Aspergillus niger were
found to have astrong phosphate dissolving ability.
Uses: 25 to 50 of the recommended Phosphorus can be reduced
depending upon the native phosphorus content ofthe soil.
Mycorrhiza: It occurs naturally in low land and upland rice. It
mobilizes the phosphorus required by rice. Mycorrhizainoculation
attempt in paddy nursery is still under study by Agricultural
Universities of India.
Since, biofertilizers are ecofriendly inputs and are safer to
the environment, farmers can adopt them and getbenefited.
G.Lawrence Amal Raj
Arul Anandar CollegeKarumathur, 625 514
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