PhD

An investigation was undertaken in three homegardens at Kalliyur
Panchayat, Thiruvananthapuram District during the period 1998 - 1999, to
analyse the structure, quantify the litter production and to assess the
decomposition characteristics of leaf litter of commonly grown multipurpose
trees. The six tree species selected for the study were mango, jack, cashew,
ailanthus, wild jack and mahogany. Decomposition studies were carried out in
the homegardens, beneath the respective tree species canopy and in an
exposed area, which served as the control plot. The standard litter bag
technique was adopted for the purpose. The changes in the soil properties
associated with the decomposition were monitored at both sites
The homegardens studied represented a multi-storied tree based
cropping system with coconut palms being the most dominant species. The
other tree species common to the three homegardens were mango, jack,
cashew, wild jack, morinda and mahogany. The farmers effectively utilized
the interspaces and theymostly relied on tuber, fodder and spice crops for
income. There was no definite pattern of arrangement but the cropping
intensities worked out for the homegardens were high.
The amount of litter accumulated in the homegardens annually by the
different tree components varied with the species, its density and prevailing
climatic conditions. Homegarden I recorded the highest amount of litter
addition followed by the homegardens 11 and III studied. The litter added

considerable amount of nutrients with nitrogen and potassium accretions
being comparatively more than that of phosphorus. The total amount of
nutrients added depended on the quantity of the litter produced and its nutrient
contents.
The fresh leaf and litter chemistry revealed comparatively lower
contents of nutrients in leaf litter in all the six species. Lignin content was
more in the litter than in fresh leaves.
Leaf litter decomposition was more rapid in the home garden compared
to that in the open plots. The dry matter loss in the leaf litter in the
homegarden followed the order jack> cashew> mango> ailanthus> wild
jack> mahogany. The linear equations best described the pattern of mass loss
from the decomposing litter. Mahogany litter exhibited the slowest decay and
recorded the lowest value for decay coefficient.
The nutrient release pattern for the different species was also worked
out. The rate of release of nutrients during decomposition differed markedly
between the different elements and most of the mobile nutrients revealed more
than 90 per cent release by the time decomposition was complete. Nitrogen,
phosphorus, potassium and magnesium were released from the litter on decay,
whereas, calcium and the micro nutrients showed trends of accumulation. The
release pattern of the' nutrients remained almost similar for each species at
both sites.

Significant improvements in the soil physical and chemical properties
were noticed due to the leaf litter decay at both sites. The soil faunal and floral
counts recorded higher populations during the rainy months and were
comparatively more in the home gardens.
The weight loss was found to be more soil moisture dependent than
soil temperature as the decay was mediated by the soil microbial biomass,
which was significantly more under the moist situations.
The initial litter quality was correlated with the rate of decomposition
and of the different chemical constituents, the lignin and lignin: N ratio had
significant influence on the rate of decomposition.
The decomposition models relating the residual mass and time elapsed
for the different species litter and nutrient equations for the different elements
at both sites were also worked out. The quadratic equation described best most
of the nutrient dynamics in the litter.