Soil productivity changes under selected exotic 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 carried out with four exotic tree species (Acacia auriculiformis, A. mangium, Casuarina equisetifolia and Swietenia macrophylla) planted at 2 m × 2 m spacing and of about 30 years age at Kerala Forest Research Institute sub-centre Nilambur during 2013-2014. The specific objective of the study was to examine the variations in soil productivity, with special reference to the beneficial microflora, due to long term occupancy of these trees. The rhizosphere soils were collected for isolation and enumeration of soil microflora like actinomycetes, bacteria, fungi, N-fixing bacteria, P-solubilises and Ksolubilising bacteria population at quarterly interval for a period of one year. The soil physico-chemical properties under the trees were also assessed. It was found that, over the years, the tree species influenced the soil physico-chemical properties. The lowest bulk density and pH were associated with tree plots compared to the treeless plots. However, the soil moisture content was not significantly different. The soil organic carbon, total nitrogen and exchangeable potassium were significantly higher (2.15%, 0.13% and 80.15 kg ha -1 respectively) in S. macrophylla and the lowest (1.38%, 0.07% and 52.34 kg ha -1 respectively) in treeless control plot. Available nitrogen and available phosphorus were significantly higher (71.6 kg ha -1 and 4.42 kg ha respectively) in A. mangium and the lowest (39.05 kg ha -1 and 4.08 kg ha -1 -1) in treeless plot. Tree species greatly influenced the soil microflora population. In general, microflora population was higher in tree plots than the treeless control. During the entire period of study, A. auriculiformis had highest mean bacteria, fungi and nitrogen fixing bacteria population while the highest population of phosphorus solubilizing microorganism and potash solubilizing bacteria was recorded in A. mangium. The highest mean population of actinomycetes was associated with C. equisetifolia. Seasonal variation in microflora population was obvious. Actinomycetes population was, generally, the lowest during rainy season and the peak population during early summer season and late summer-II. The bacterial population was the maximum during rainy season and the lowest during early summer season. The fungal population was more in both the late summer (2013 and 2014) seasons and the lowest in the winter season. Nitrogen fixing bacteria population was highest in the late summer-I and found to decrease through the rainy season and winter season. The populations of phosphate solubilizers and potash solubilizing bacteria were highest in late summer-I season and lowest in the rainy season (phosphate solubilizer) and winter season (potash solubilising bacteria). A. mangium had the maximum height (19.90 m) followed by C. equisetifolia, A. auriculiformis and the lowest was for S. macrophylla. Diameter at breast height was also highest in A. mangium (24.31 cm) followed by S. macrophylla, A. auriculiformis and C. equisetifolia The present study highlighted the influence of tree species on microflora
population. Microflora population was found to be significantly higher in tree species compared to nearby treeless control plot and was found to be varying according to seasons. All the tree species have shown higher soil nutrient content than treeless plot. These four exotic tree species in the present study is seen to take part actively in the improvement of soil quality and soil health which are the major determinants of sustainable soil productivity.
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