Availability indices for stressed nutrients for coconut (Cocos nucifera L) in an ultisol
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Date
2003
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Department of Soil Science and Agricultural Chemistry, College of Horticulture, Vellanikkara
Abstract
The present study was conducted with an objective to analyse the soil-plant
system, the levels and interactions of nutrient ions in soil, soil solution and plant thereby
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finding out the contributing factors to yield. The importance of the term relative intensity
lies in the fact that the contribution of mineral elements to growth and yield of plants
depend much on the relative amount of one element with respect to the others rather than
the absolute content of individual elements. To study the ionic interactions and to
unravel the role of Net Ionic Equilibrium based on Ratio Law on soil plant system, a
sample of fifty phenotypically identical palms varying in yield from 14.4 to 84.4 nuts
palm" year"! grown under an Ultisol were selected.
Index leaf samples were collected during pre and post monsoon seasons from 25
palms each from high yielding and low yielding groups. Soil samples were also collected
from the basins of these palms during the same seasons at 30 cm (surface) arid 60 cm
(subsurface) depths. Soil solutions at saturation point were extracted from the surface
samples by centrifugation technique. These leaf, soil and solution samples were analysed
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for different nutrient ions, and the NIE ratios in these three phases were worked out with
respect to K and Na.
The soil samples were acidic in nature and the variation in rhizosphere pH must
have definitely influenced the solubility as well as absorption of different nutrient ions.
In the case of available nutrients, the micro nutrients showed significant direct
relation with yield both for high and low yielding populations. This might be due to their
restricted availability due to aerobic oxidised condition where Fe and Mn might have
been precipitated and got into unavailable forms.
The BaCh exchangeable ions and the CEC derived from summing up of these
exchangeable ions influenced yield directly.
Exchangeable K had got a significant dominance in deciding the NIE ratio in soil,
solution and in index leaves. Exchangeable K controlled the soil solution concentration
of K which in turn controlled the NIE ratio in solution and the ratios in plant.
Exchangeable K directly controlled the plant K content and plant K was positively
and significantly correlated with the NIE ratios in plant and these ratios were positively
and significantly correlated with yield.
The negative significant correlation of exchangeable K with plant Mn and Zn
revealed the antagonistic effect of exchangeable K in restricting the absorption of Mn and
Zn by plants.
Among the ionic concentrations in soil solution, Fe was positively and
significantly correlated with yield in both the seasons. Soil solution concentrations of Ca
and Mg were antagonistically and significantly related with plant Mn content. Potassium
content and the NIE ratio in index leaves were found to have a significant direct relation
with yield in the pre-monsoon season. Potassium, Ca and Mg were the dominant cations
in plant deciding the total cation concentration in index leaves.
The NIE ratios between the exchangeable ions, the ions in soil solution and the
ions in index leaf samples were mutually, .positively and significantly correlated among
themselves. This lead to the conclusion that there exists a constancy in the relative
proportion of nutrient ions in the entire soil-plant system which followed Ratio Law.
The study lead to the conclusion that the soil test values of the individual ions
alone or the plant content of individual ions alone can't give a clear picture of optimum
nutrient requirements for the plant. The relative concentration of K in soil through the
~ concentration in soil solution was found to govern the relative concentration in plant
which in turn influenced the yield.
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Citation
172150