MSC

A field investigation was conducted with four important indigenous tree
species viz. Hopea parviflora Bedd., Artocarpus hirsutus Lamk., Pterocarpus
marsupium Roxb, and Pterocarpus santalinus L.f. of about 30 years of age and
planted at 2 m×2 m spacing at Kerala Forest Research Institute sub-centre Nilambur,
India for a period of one year (May 2013 to May 2014). The specific objective of the
study was to monitor the soil productivity changes due to long term occupancy of
four indigenous trees with special reference to the beneficial soil microflora. The
rhizosphere soil samples were collected for the isolation and enumeration of
microbial population at quarterly interval for a period of one year. The population of
bacteria, fungi, actinomycetes, nitrogen fixing bacteria, phosphate solubilising
bacteria and potash solubilising bacteria were estimated by serial dilution method.
The soil physico-chemical properties and the growth of trees were also observed.
The highest microbial population, during the entire study period, was recorded
in Artocarpus hirsutus and the lowest in treeless control plot. Artocarpus hirsutus
recorded the maximum bacteria, fungi, actinomycetes, nitrogen fixing bacteria and
phosphate solubilising microorganism. Potash solubilizing bacteria were recorded
maximum in Hopea parviflora plots. The highest bacterial population observed in
late summer and rainy season and the lowest recorded during early summer season.
The highest fungal population recorded in late summer season and the lowest during
winter season. Early summer season recorded the highest actinomycetes population
and lowest in late summer season. The highest population of nitrogen fixing bacteria
and phosphate solubilising microorganism observed in the winter season and the
lowest population during early summer season. Potash solubilizing bacteria recorded
highest during the summer seasons (late summer-Ι and late summer-II seasons) and
lowest in the rainy season. In the final sampling (late summer) also, A. hirsutus was
found to harbour maximum bacteria, nitrogen fixing bacteria, phosphate solubilising bacteria and potash solubilising bacteria. However, the highest fungi and
actinomycetes associated with Pterocarpus santalinus.
The long term occupancy of the indigenous tree species was found to have
influenced the soil physico-chemical properties. The soil moisture and bulk density
was distinctively superior in the wooded lands as compared to the treeless open area.
The soil organic carbon (2.25%), available nitrogen (17.80 kg ha
-1
), total nitrogen
(0.16%) and exchangeable potassium (70.70 kg ha
-1
), were also significantly higher
in H. parviflora. The most acidic soil was also found in H. parviflora while the least
acidic was A. hirsutus plots. The maximum height (12.41m) and the dbh (16.25 cm)
were recorded in Pterocarpus santalinus The present study throws light into the intimate relation between the types and
nature of soil microflora populations and their positive influence on the microsite
enrichment aspects of promising indigenous tree species. The information will aid in
preferential selection of these tree species along with crops into different tree farming
systems where the ecosystem sustainability is of greater relevance. In general, all the
four indigenous tree species recorded significantly higher microflora population and
greatly improved physico-chemical properties than treeless plot due to long term
occupancy of trees.