MSc

A study was done at the College of Agriculture, Vellayani during
1994-95 to quantify the different forms of potassium and to investigate
the inter-relationships of these forms with other soil fertility parameters.
Soil samples were collected from ten locations each, of the two major wet
land rice soils of Kerala selected for the study viz., lateritic alluvium of
Pattambi (brown hydromorphic) and Onattukara sandy soil (greyish
Onattukara) of Kayamkulam. Incubation studies were also carried in both
soil types, with and without applied potash, for a period of two months.
The study revealed that considerable variation existed in the
physico-chemical properties of the two soils. The lateritic alluvium of
Pattambi was clayey, high in chloride, organic matter, active iron, CEC,
ECEC, exchangeable Ca, Mg and sum of bases and was low with respect
to coarse sand and available phosphorus contents and was less acidic as
compared to the Onattukara sandy soils of Kayamkulam. The latter was
loamy sand in texture with a high content of coarse sand fraction, more
acidic, high in phosphorus content and low in clay, chloride, organic matter,
active iron, CEC, ECEC, exchangeable Ca, Mg and sum of bases in
comparison to the former.


Fractionation studies revealed that the Pattambi soils had a higher
content of total K, HN03K and fixed K as compared to that of Kayamkularn
soils.
The high positive correlation of exchangeable K with the available
K fraction in both the soil types justifies the existence of a dynamic
equilibrium between the two fractions.
The .negative correlation of exchangeable and available fractions
of K with active iron observed in Pattambi soils was contrary to earlier
observations in this regard.
Though comparatively high in organic matter, the effect of soil
reaction on the available K status was not considerable in Pattambi soils
as compared to Kayamkulam soils. This led to the conclusion that
management of organic matter in tropical soils is important to maintain
the available K status for sustainable farming.
The positive inter correlation obtained between lattice K and total
K indicated that the major portion of soil potassium existed in the lattice
form. The positive and significant association of other forms of potassium
was indicative of the existence of a dynamic equilibrium between these
forms of K.


Potassium fixation was found to be a constraint in Pattambi soils
especially with the addition of potassic fertilisers. Hence this should be
given due consideration while formulating cost-effective and efficient
potassium management strategies since the major chunk of potassic
fertilisers are imported in our country.