What is a Bio-fertilizer?
Most fertilizers add nitrogen to the soil. This can
be done via chemical fertilizers, or through a process called biological
nitrogen fixation (BNF). On a worldwide basis it is estimated that about
175 million tons of nitrogen per year is added to soil through biological
nitrogen fixation (BNF). The term bio means living;
so bio-fertilizers refer to living, microbial inoculants that are added to
the soil. These bio-fertilizers are products consisting of selected and
beneficial microrganisims, which are known to improve plant growth through
supply of plant nutrients.
The soil microorganisims used in biofertilizers
are: Phosphate Solubilizing microbes, Mycorrhizae, Azospirillum,
Azotobacter, Rhizobium, Sesbania, Blue Green Algae, and Azolla. Let's go
through these groups in a little detail in order to understand their role
in bio-fertilizers, which can be used to make rich, living soil that is
suitable for coffee plants.
Phosphate Solubilizing Microbes:
Phosphorus is an important nutrient for plants.
There are several microorganisims which can solubilize the cheaper sources
of phosphorus, such as rock phosphate. Bacteria like Pseudomonas striata,
and Bacillus megaterium are also important phosphorus solubilizing soil
microorganisims. Many fungi like Aspergillus and Penicillium are potential
solubilizers of bound phosphates. They solubilise the bound phosphorus and
make it available to the plant, resulting in improved growth and yield of
crops. Soil phosphates are rendered available to plants by soil
microorganisims through secretion of organic acids. Therefore, phosphate
dissolving soil microorganisims play some part in correcting phosphorus
deficiency in plantation soils. They may also release soluble inorganic
phosphate into soil through decomposition of of phosphate rich organic
compounds. These microbial inoculants can substitute almost 20 to 25% of
the phosphorus requirement of plants.
Phosphate solubilising microbes can also be inoculated to coffee husk
along with rock phosphate while preparing compost to enrich the compost
with available phosphorus.
The term "mycorrhizae" refers to fungus
associated with plant roots. These fertilizers are divided into
ectotrophic and endotrophic or the vesicular arbuscular mycorrhiza (VAM)
categories. Most plants depend on their mycorrhizal association for
adequate uptake of nutrients (especially the immobile ions such as
phosphate, zinc and micronutrients) and survival in natural ecosystems.
Mycorrhixal association stimulates branching of the root and increases the
absorption surface of the root. Other benefits include tolerance to
drought, high soil temperature, soil toxins, and extreme Ph levels, as
well as protection against root pathogens. This is why, When trees are
introduced to new regions, inoculation of soil with mycorrhizal fungi is a
necessary prerequisite for the establishment of the trees.
Azospirillum are nitrogen-fixing bacteria that
lives in a symbiotic relationship in the root cortex of several tropical
crops. They stimulate plant growth through nitrogen fixation and
production of growth subustances like auxins, gibberellins and cytokinin.
It is estimated that almost 10 to 15% of the required nitrogen can be met
by Azospirillum biofertilizer.
Azotobacter are free-living, nitrogen-fixing
bacteria and are known to produce several plant growth promoting
subustances. In addition to nitrogen fixation by these bacteria, they are
also known to protect plants against pathogenic microorganisims either by
discouraging their growth or by destroying them. These inoculants need
more attention in view of their triple action of nitrogen fixation,
bio-control, and production of plant growth regulators.
Rhizobium bacteria, basically form root nodules in
leguminous plants and fix atmospheric nitrogen in a symbiotic association.
The Rhizobium bacteria gives nitrogen to the plant and the plant gives
protection to the bacteria from oxygen damage by harbouring it inside the
Many legumes are grown and then turned into the
soil while they are still green to enrich soil nitrogen. Sesbania is a
green manure plant which forms both root and stem nodules in association
with rhizobium and thereby fixes more atmospheric nitrogen. These legumes
produce ten times more nodules than other legumes and have a very high
capacity to fix atmospheric nitrogen. Apart from enrichment of soil
nitrogen, green manuring enriches the phosphorus, calcium, sulphur and
other micronutrient of the soil.
Blue Green Algae:
Blue Green Algae (BGA) or Cyanobacteria have the
ability to carry out both photosynthesis as well as nitrogen fixation.
They belong to the order Nostocales and Stigonematales. Algal flakes are
grown and then broadcasted.
Azolla is a floating fern which harbours a blue
green algae in its leaf cavities. The fern multiplies very fast with the
symbiotic association of the algae and this rapid multiplication creates a
huge amount of biomass on the surface of the water. It is then harvested,
dryed and used as biofertilizer.
Bio-fertilizers (also known as microbial
inoculants) improve soil fertility and enhance nutrient uptake and water
uptake in deficient soils, thereby aiding in better establishment of
plants. Bio-fertilizers also secrete growth subustances and antifungal
chemicals, as well as improve seed germination and root growth. The dual
effects of phosphorus mobilizing fungi and specific nitrogen-fixing
bacteria can cater to the needs of the current coffee plantation sector.
Thus, the use of bio-fertilizers will effectively
enrich the soil and will cost less than chemical fertilizers, which harm
the environment and deplete non-renewable energy sources