PhD

A study entitled ‘Technology refinement for biochar production and
evaluation of its effect on soil health and crop productivity’ was carried out at the
Department of Soil science and Agricultural Chemistry, College of Agriculture,
Vellayani, during March 2015 to June 2016. The objective of the study was
refinement of technology for micro level biochar production from tender coconut
husk and evaluation of its effect on soil health, yield and quality of banana (Musa
spp.) in the field.
A modified design of micro biochar kiln for the pyrolysis of tender coconut
husk to biochar was developed. The micro kiln consists of a temperature monitoring
enabled, double barrel reactor unit with chimney and a cooling assembly for
condensation and cooling of syngas. The reactor unit had a biomass capacity of 30
kg. The pyrolytic conversion happened at temperature >350 oC and time required was
90 minutes. Characterization of biochar produced was done by standard procedures
and it had an alkaline pH (8.53), CEC (15.26 cmol kg-1), AEC (5.64 cmol kg-1), C: N
(46.11), C:P (175.25), C:S (259.62) and C:N:P:S (350:7.5:2:1) ratios. Electrical
Conductivity, total C, N, P, K, Ca, Mg, S, Fe, Mn and B were 1.70 dS m -1, 70.10 %,
1.52 %, 0.40 %, 2.26 %, 0.54 %, 0.46 %, 0.27 %, 89.9 mg kg-1, 2.84 mg kg-1 and 6.78
mg kg-1 respectively. The heavy metal contents (Pb, Cd, Ni, Cr, Zn and Cu) were
very low when compared to the maximum allowed threshold levels. The syngas
produced during pyrolysis was analyzed by gas chromatography and its composition
was carbon dioxide (67.70%), methane (22.89%), oxygen (8.74%), hydrogen (0.66%)
and n-Butane (0.001%) on normal mol % (dry) basis. Carbon monoxide and nitrogen
were absent. The biochar recovery percentage was 50 %, which was 17 % more than
the previous model of biochar kiln. The quantity of syngas produced was
comparatively less. The composition of syngas produced revealed that it can not be
used as a bioenergy source because the methane content is less. There was no

production of bio oil during pyrolysis. All these advantages qualifies this refined
technology as the most effective in carbon sequestration and safe waste management.
In order to find out the effect of biochar on soil health and crop productivity, a
field experiment was carried out with nendran banana as test crop in Loamy,
Kaolinitic, Isohyperthermic, Typic Kandiustults belonging to Vellayani series.
Treatment combinations were T1- Package of practices recommendation, T2- BC @ 5
kg plant-1 + NPK as per POP, T3- BC @ 10 kg plant-1 + NPK as per POP, T4- BC @ 5
kg plant-1 + 75% NPK as per POP, T5- BC @ 10 kg plant-1 + 75% NPK as per POP,
T6- FYM 10 kg plant-1 + (NPK + secondary and micronutrients as per Soil test based
recommendation), T7- BC @ 5 kg plant-1 + (NPK + secondary & micronutrients as
per STBR), T8- BC @ 10 kg plant-1 + (NPK + secondary & micronutrients as per
STBR), T9- BC @ 5 kg plant-1 + 75% (NPK + secondary & micronutrients as per
STBR), T10- BC @ 10 kg plant-1 + 75% (NPK + secondary & micronutrients as per
STBR) and T11- BC alone 10 kg plant-1.
Plant biometric characters like plant height at 2, 4, 6 and 8 months after
planting, number of leaves per plant at 2 and 6 MAP and pseudostem girth at 4 and 8
MAP were highest in the treatment (T10) where biochar @ 10 kg plant-1 + 75% (NPK
+ secondary & micronutrients as per STBR) was applied followed by 5 kg biochar +
75% of NPK as per POP (T4). The total dry matter production was significantly
higher with biochar @ 10 kg plant-1+ 75 % of STBR. Biochar @ 10 kg plant-1 added
with 75% of STBR resulted in the highest bunch weight, number of hands per bunch,
number of fingers per bunch and both length and girth of the index finger. 10 kg
biochar along with 75% STBR enhanced the physical properties of the soil by
imparting 57.11 % increase in the WHC, 35.32 % increase in porosity and 7.31 %
decrease in the bulk density than application with FYM + NPK as per POP. A
significant increase in soil pH was observed in the biochar based treatments as
compared to the FYM applied treatments with a 0.6 units increase in pH in the

treatment which received 10 kg biochar + 75% STBR. The highest OC content of
1.45 % and a 100 % increase in CEC of the soil was realized when biochar @ 10 kg
along with 75 % of STBR were applied instead of FYM based POP recommendation.
The biochar application @ 10 kg with 75 % of STBR significantly increased the soil
available N, K, Mg and B at the active growth and harvest stages of banana. Zn
content was highest in this treatment throughout all stages. The superiority of biochar
based treatments as compared to FYM based treatments in promoting the growth and
development of soil microorganisms in the rhizosphere was evident with a 55.9 %
enhancement in soil dehydrogenase activity in the treatment where biochar @ 10 kg
plant-1 + 75% STBR was applied.
Biochar @ 10 kg plant-1 with 75 % STBR (T10) recorded highest foliar N, K,
Mg, S, Fe, Mn, Zn content, as well as highest nutrient use efficiency of 50.4 %. Fruit
quality parameters like TSS, ascorbic acid content and shelf life of fruits were found
to be superior for the same treatment. The highest B:C ratio of 2.38 was also found in
T10 treatment. Based on this a biochar based nutrient mix was prepared by mixing 10
kg biochar with urea
260.21g,
MOP
528.75g
and MgSO4 23.44g for Typic Kandiustults of
Vellayani series.
Hence it may be concluded that the biochar produced by modified micro
biochar kiln had ideal physical and chemical properties that qualify it to be used as a
good soil amendment which is environmentally safe and contributing to the soil
carbon pool. Biochar application in general, and biochar (10 kg plant-1) along with 75
% soil test based recommendation in particular, enhanced the soil physical properties,
decreased soil acidity, promoted rhizospheric microorganisms, increased the soil
fertility status enabling efficient nutrient use and resulted in higher growth, profitable
yield and superior fruit quality of banana.