Evaluation of growth of teak (Tectona grandis) managed as farmer woodlots in dry and intermediate zones of Sri Lanka with reference to selected soil physical and chemical properties
by
Thilina Jayarathne and Upul Subasinghe
by
Thilina Jayarathne and Upul Subasinghe
The replanting activities using new species were started in Sri Lanka as early as 1680s with the introduction of teak. Since then teak has become widely planted in dry and intermediate zones of the Island. One of the main methods of establishing teak plantations was by the farmer woodlots with a participatory approach.
However, the growth studies of those woodlots have not widely been conducted in Sri Lanka to identify the social issues and the management problems. Therefore this study was conducted to identify the growth of teak under diffferent soil parameters of farmer woodlots and to identify the possible relationships among growth parameters and soil properties. For this purpose, 17 teak plantations were selected for the data collection with age varying from 8 to 13 years. Those plantations were seleced from Anuradhapura and Polonnaruwa Forest Divisions to represent the dry zone and from Kurunegala Forest Division to represent the intermediate zone. Three farmer woodlots from each plantation were randomly selected and three sample plots were laid in each woodlot. Dbh and total height were measured for all trees in each sample plot. Bulk density, pH, mechanical properties, colour, soil nitrate, phosphorus, potassium, magnesium and calcium were measured using standard methods at the laboratory for the collected soil samples.
After statistical and graphical analysis of those variables, it was observed that both height and dbh indicated exponential relationship with plantation age. The sand% of the selected plantations varied from 68.6 to 96.4%. The clay% varied from 0.3 to 7.5%. Silt% changed from 3.2 to 27.2%. The observed soil types were belonged to sand, sandy loam and loamy sand. The heighest bulk density was 2.313 gcm-3 while the lowest was 0.896 gcm-3. The observed nitrate values varied from 2.133 to 7.466 ppm. The highest and lowest values of phosphorus concentration were 254 and 56 ppm respectively. Potassium varied from 4.126 to 8.326 ppm. However, calcium was not detected for most of the soil samples. It was important to note that the pH values were below 7.0 for all plantations.
When the sand% of soil increased, the growth of teak showed a decreasing trend and higher growth rates were observed with increasing clay%. Moreover, both height and a growth index developed for this study showed an increase with high amounts of nitrogen. Moreover, it was observed that soil nitrogen and phosphorus tend to increase with increasing clay% of soil. Growth of teak in most farmer woodlots are in between height classes II and III according to the yield tables published by Sri Lanka Forest Department.
However, the growth studies of those woodlots have not widely been conducted in Sri Lanka to identify the social issues and the management problems. Therefore this study was conducted to identify the growth of teak under diffferent soil parameters of farmer woodlots and to identify the possible relationships among growth parameters and soil properties. For this purpose, 17 teak plantations were selected for the data collection with age varying from 8 to 13 years. Those plantations were seleced from Anuradhapura and Polonnaruwa Forest Divisions to represent the dry zone and from Kurunegala Forest Division to represent the intermediate zone. Three farmer woodlots from each plantation were randomly selected and three sample plots were laid in each woodlot. Dbh and total height were measured for all trees in each sample plot. Bulk density, pH, mechanical properties, colour, soil nitrate, phosphorus, potassium, magnesium and calcium were measured using standard methods at the laboratory for the collected soil samples.
After statistical and graphical analysis of those variables, it was observed that both height and dbh indicated exponential relationship with plantation age. The sand% of the selected plantations varied from 68.6 to 96.4%. The clay% varied from 0.3 to 7.5%. Silt% changed from 3.2 to 27.2%. The observed soil types were belonged to sand, sandy loam and loamy sand. The heighest bulk density was 2.313 gcm-3 while the lowest was 0.896 gcm-3. The observed nitrate values varied from 2.133 to 7.466 ppm. The highest and lowest values of phosphorus concentration were 254 and 56 ppm respectively. Potassium varied from 4.126 to 8.326 ppm. However, calcium was not detected for most of the soil samples. It was important to note that the pH values were below 7.0 for all plantations.
When the sand% of soil increased, the growth of teak showed a decreasing trend and higher growth rates were observed with increasing clay%. Moreover, both height and a growth index developed for this study showed an increase with high amounts of nitrogen. Moreover, it was observed that soil nitrogen and phosphorus tend to increase with increasing clay% of soil. Growth of teak in most farmer woodlots are in between height classes II and III according to the yield tables published by Sri Lanka Forest Department.
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