PhD

An investigation entitled “Efficiency of vermiconversion and
decomposition of farm residues on soil health, yield and quality of banana (Musa
spp.)” was undertaken at College of Horticulture and Banana Research Station,
Kannara during 2013-2015. The objectives of the study were to compare the
efficiency of native and exotic earthworms on vermiconversion of farm residues
and the effects of different modes of vermicomposting on soil health, yield and
quality of banana and to evaluate the in situ decomposition of banana crop
residues
An experiment with seven treatments and three replications was laid out in
randomized block design to assess the composting efficiency of native and exotic
earthworms. Seven treatments included absolute control as soil (S), ex-situ
compost in silpaulin vermibed without earthworms (Ex-C), ex-situ vermicompost
in silpaulin vermibed using Perionyx excavatus (Ex-P), ex-situ vermicompost in
silpaulin vermibed using Eisenia foetida (Ex-E), in-situ vermicompost in banana
planting pits using Perionyx excavatus (In-P), in-situ vermicompost in banana
planting pits using Eisenia foetida (In-E), in-situ compost in banana planting pits
without earthworms (In-C). In the next study, the prepared composts were tested
along with recommended doses of fertilizers and FYM to assess their effects on
growth, yield and crop quality of banana var. Nendran in RBD with seven
treatments replicated thrice. The treatments were absolute control (S),
300:115:450g N:P2O5:K2O plant-1 + FYM at the rate of 20 kg plant-1 (POP) , exsitu
vermicompost in silpaulin vermibeds with Perionyx excavatus at the rate of
20 kg plant -1 (Ex–P), ex-situ vermicompost in silpaulin vermibeds with Eisenia
foetida at the rate of 20 kg plant -1 (Ex–E) , in-situ vermicompost in crop pits with
Perionyx excavatus at the rate of 20 kg plant -1 (In-P), in-situ vermicompost in
crop pits with Eisenia foetida at the rate of 20 kg plant -1 (In-E), in -situ compost
at the rate of 20 kg plant -1 (In-C). After the harvest of the crop, the entire
residues from each plant was incorporated in the respective crop pits and the insitu
degradation of the banana residues was monitored. The salient findings are
summarized as follows
In the first trial, the composting efficiency of native and exotic earthworms under
different modes of composting was compared. Chemical properties of compost
like pH, electrical conductivity, and content of primary nutrients were
significantly affected by modes of composting. Exotic earthworms like Eisenia
foetida produced higher auxin content in the compost whereas Perionyx excavatus
registered higher dehydrogenase activity under ex-situ mode of composting. The
total microbial load was recorded in the compost prepared without earthworms
under both modes of composting. Compost yield was more in ex-situ composting
methods and Eisenia foetida was more efficient in composting as compared to
Perionyx excavatus. Humic acid characterization by Fourier Transform Infra-Red
spectroscopy revealed a similar spectra from different treatments and were found
to be characterized by aromatic rings and triple bonded skeleton. Presence of
relatively higher quantity of polysaccharide like substances was observed in insitu
mode of composting. The spectra of humic acids for ex-situ composts
prepared using Perionyx excavatus revealed a nitrate band of characteristic shape
appearing prominently. Perionyx excavatus produced humic acids with high
aromaticity both under ex-situ and in-situ mode of composting. Scanning electron
microscopy revealed neo-formed CaCO3 nodules embedded in humic acids in the
ex-situ vermicompost produced by Eisenia foetida. Transmission Electron
Microscopy of humic acids indicated a globular structure for vermicompost
prepared by Perionyx excavatus and a lamellar structure with voids for
vermicompost prepared using Eisenia foetida.
On field experimentation with different treatments using Nendran banana as the
test crop, the highest yield was obtained for combined application of fertilizers
and farm yard manure as per POP. Number of fingers per hand and number of
functional leaves were found to influence the yield, irrespective of treatments. The
number of days to bunching and harvest was significantly reduced for banana
under in-situ composting. Higher content of total, reducing and non-reducing
sugars were observed for in-situ composting treatments. On the contrary, higher
titratable acidity was recorded for the control treatment. Both vitamin C content
and sensory parameters were complimentary for POP treatment. Increased
absorption and translocation of nutrients such as N, P, K and Mg in fruits were
observed under organic nutrition using Perionyx excavatus.
For the next study, the residues of banana were added to the respective pits for
monitoring the carbon and nitrogen mineralization. The carbon mineralization
with respect to time was fitted to single pool exponential model to derive the rate
of mineralization and half-life. It revealed crop residues pre-treated with
vermicompost using exotic earthworms had a higher rate of C cumulative
mineralization. Nitrogen addition by both exotic and native species of earthworms
were almost similar under in-situ conditions. The banana residue decomposition
by Eisenia foetida was about 3.5 times higher than that of Perionyx excavatus.
Calcium content of Perionyx excavatus pre-treated residues added the maximum
calcium to the soil.