Biochar
Biochar is charcoal that is produced by pyrolysis of
biomass viz., rice straw, in the absence/limited of oxygen, and is used as a
soil ameliorant for both carbon sequestration and soil health benefits. Controlled
pyrolysis of rice straw could produce biochar which not only reduces greenhouse
gas emissions but at the same time sequester carbon in soil for long time, when
added to soil as amendment. Biochar serves as a sink for atmospheric CO2 because
of its reactive surfaces and recalcitrant aromatic structure. During pyrolysis,
about 50% of the carbon content in the crop residues is immediately released as
gas or volatile compounds, which could be effectively used as energy sources;
the remaining carbon in biochar is highly recalcitrant and contributes to sequester
C once applied in soil.
Use of rice Straw-biochar.
After the harvest of rice crop, huge quantity of rice
straw is burnt in open fields leading to air pollution. Rice straw serves as
raw feed material for biochar production. There are various goals for
utilization of SDB. It has high potential to be used as soil amendment material
to improve soil quality and subsequent yield. However, other than soil
application biochar can be used for many other purposes.
Basic uses include drinking water
filtration, sanitation of human and kitchen wastes, and as a composting
agent. Other uses include as adsorber in functional clothing, insulation in the
building industry, as carbon electrodes in super-capacitors for energy storage,
food packaging, wastewater treatment, air cleaning, silage treatment agent
and/or feed supplement.
Preparation of biochar from rice straw (small
scale)
The biochar is produced by pyrolysis of husk at
350°C for 3-4 hours using indigenous furnace or kiln at controlled temperature
and restricted aeration.
Steps for biochar preparation
Step 1:
Collection of straw from field after rice harvest
Step 2:
Physical cleaning of straw by drying the straw and beating it to remove the
small mud clods.
Step 3:
Feeding the straw to biochar making furnace or kiln.
Step 4:
Igniting the straw and covering it suitably to restrict the flow of oxygen
Step 5:
Ensure that the temperature inside the furnace/ kiln is about 300-400oC
by regular monitoring with thermal sensor.
Step
6: Stable biochar is prepared in 3-4
hours. Take the biochar out from the furnace after the furnace is sufficiently
cool to handle.
Doses
of Rice straw biochar for Rice crop Production
Rice straw derived
biochar (SDB) application can be applied at a rate of 2 t/ha to 10 t/ha
depending on availability, feasibility and on soil need basis. Rice crop yield
improve with application rates of 2 t/ha and above. In soils with high acidity, the application
rates need to be higher to bring the soil to neutrality to achieve an optimum
soil condition for crop production. Application of 10 t/ha or more may be
required only in acid soil with pH<5.0. Earlier, long terms experiment
(>5 years) conducted with rice husk derived biochar suggest that higher
doses in neutral soils do not have any negative effect on grain yield or soil
properties.