Soil productivity changes under selected indigenous forest tree species with special reference to beneficial microflora
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Date
2014
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Department of Silviculture and Agroforestry, College of Forestry, Vellanikkara
Abstract
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.
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