MSc

A study was conducted at College of Forestry, Vellanikkara, KAU,
during the period 1994-1996 to identify and assess the nutritional factors
limiting productivity of teak plantations, of different age groups belonging
to different site qualities, spread through out the State of Kerala. The study
was aimed to find out the influence of nutrient status of soil and leaf on the
growth as represented through volume and current annual increment in
basal area per tree. Another objective was to find out the influence of soil
characteristics like pH, organic carbon and nutrient contents on foliar
nutrient concentration of teak. The leaf samples were analysed for N, P,
K, Ca, Mg, Fe, Mn and Zn concentrations. The soil samples were analysed
for pH, organic carbon, available P, total N and exchangeable K, Ca, Mg, Fe
and Zn. The whole set of 300 trees was divided into three age groups as
< = 20 years, > 20 and < = 40 years and > 40 years and stepwise
regression was carried out by taking volume as dependent variable for each
group separately. The resultant equations in stepwise regression were
utilized to characterize the nature of response surface and to find the
optimum levels of soil attributes and foliar nutrient elements. For analysing
the relationship between soil attributes and foliar nutrient concentrations a
technique called canonical correlation analysis was used.
The relation between leaf nutrient status and tree volume was feeble
in all the three age groups. In all the three age groups, the critical nutrient
concentrations with respect to tree volume do not seem to be attained by
the levels of nutrients available in the present data set, indicating a increase
in tree volume by adequate supply of the appropriate nutrient elements.

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The relation between tree growth and nutrient status of soil was
stronger compared to the relation between the tree growth and nutrient
status of soil. For the first two age group selected, the models were linear
in nature. For the older plantations (Age > 40 years), almost 50 per cent
of the variation in tree volume was explained by the soil nutrient levels. For
this age group soil phosphorus had a quadratic term in the model and the
point of maximal response for phosphorus was predicted at P = 26.66 ppm.
The relationship between current annual increment in basal area per
tree and nutrient status of leaves and soil was also linear. Age related
change in current annual increment is positively modified by the level
of soil nitrogen.
To find out the relationship between the leaf attributes and soil
attributes canonical correlation analysis was used. For the younger age
group (age < = 20 years) soil organic carbon had a significant positive
influence on leaf nitrogen and leaf potassium concentrations while it had a
negative effect on leaf Fe and leaf Mg concentrations. Also significant
positive correlation was seen between leaf Ca and soil Ca for all the age
groups.
The canonical correlation analysis showed that as the age of the
plantations increases and the canopy closure occurs, the leaf nutrient
contents influence the soil fertility attributes to a greater extend due to the
effect of litter fall.