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Potassium is a versatile vital nutrient for regular plant and animal growth and
development. It is regarded as a "quality nutrient" because of its multifunctional role in
metabolism. Kaolinite clay minerals prevalent in lateritic soils of Kerala, have lower
activity and prevent the retention of available forms of potassium. Potassic fertilisers
are often overlooked in fertiliser schedules due to their high unsubsidized cost. There
are some K rich organic sources that are ignored by the farmers and are left or burnt in
the soil. The utilisation of organic K resources like rice straw and plantain compost
made from banana wastes are regarded good alternatives for synthetic potassic
fertilisers. The present investigation consisted of three experiments viz., (i) assessment
of decomposition dynamics of rice straw and its K release, (ii) K adsorption study on
rice straw and prepared plantain compost and (iii) an incubation study in lateritic soil
with different sources of potassium.
The decomposition rate of rice straw has increased with the period of its incubation and
it showed only a partial decomposition of 51.9 % at 90 days due to the presence of more
amount of lignin, cellulose and hemicellulose content which takes more time for its
degradation. The potassium release rate increased to 84.28 % at 90 days of its
decomposition.
The adsorption study on rice straw with different levels of KCl solution at different
periods of decomposition revealed that as the solution concentration increased, the
quantity of K adsorbed on rice straw also increased along with the increase in incubation
period. Similarly, plantain compost that was prepared using vermi technology also
showed an increased trend in the value of quantity of K adsorbed on compost as the
KCl concentration increased. Because of its smaller particle size and larger surface area,
plantain compost has stronger adsorption and buffer power than rice straw.
Rice straw with potash (T1), plantain compost with potash (T2), wood ash, FYM with
potash (T3), rice straw with lime and potash (T4), plantain compost with lime and
potash (T5), wood ash, FYM with lime and potash (T6), lime and potash (T7), potash
alone (T8), and absolute control (T9) treatments were used in the incubation study. The
physico-chemical characteristics of soil such as pH, EC, organic carbon, available N,
P, Ca, Mg, S, Fe, Cu, Zn, and Mn were determined at initial and final days of incubation.
Data on the different fractions of soil K indicated that the treatment containing rice
straw with lime and Muriate of potash (T4) showed the higher value of total K,
exchangeable K and non-exchangeable K after 90 days of incubation. The reason might
be that the presence of more inter planar sites in rice straw has trapped the K+
ions in
fixed form since the material is not completely decomposed. At the same time
incorporation of rice straw has enhanced the CEC of the soil thus enhancing greater
adsorption of exchangeable K from unavailable forms by mass effect.
The current study showed that combining organic K resources with lime and K
fertilisers resulted in significant increases in soil K fractions. Integrated application of
rice straw with lime and K fertiliser can be considered as the best method for long-term
cultivation because it has the ability to retain and release more K, particularly nonexchangeable, exchangeable, and total K, allowing for continuous uptake of K by the
crops for normal growth and development. The usage of plantain compost in
combination with lime and Muriate of potash has resulted in increased availability of K
as well as micronutrients by maintaining favourable pH.