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The present study entitled ‘Ion interactions and rice nutrition in acid saline
Pokkali soils’ has been carried out to assess the ion interactions in acid saline Pokkali
soil, to identify the chemical constraints in plant nutrition and emerging deficiencies
or toxicities of nutrients in Pokkali soils. For this purpose, soil samples and plant
samples were collected from eight Pokkali locations of Kottuvally panchayath and
one from RRS, Vyttila. The eight locations included Mundothuruth, Kalappumpadi,
Muppathezhukettu, Periyali, Diamond, Kaitharam, Padinjare Kaitharam and
Thathapilli. The soil samples were collected during three stages of cultivation namely
mound preparation, mound dismantling and harvest. Two growth stages namely
maximum tillering and harvest were selected for the collection of plant samples.
The soil samples were characterized for physical (soil texture), chemical
(pH, EC, CEC, exchangeable cations, ESP, SAR, percent cation saturation, anions,
available N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, B, Al and Na) and biological attributes
(MBC, DHA and organic carbon) and the plant samples were analyzed for nutrient
contents and uptake. The measured attributes were analysed by two- way analysis of
variance using statistical package operational statistics. Canonical analysis was done
to find out the decisive ions in Pokkali soils. The t-test was carried out to identify the
toxicity and deficiency of nutrients in Pokkali soils and rice. The correlation of Net
Ionic Equilibrium (NIE) ratios of K, Mg, Cu and Na with various soil parameters
were carried out to identify ion interactions in soil.
Analysis of variance revealed that, among various measured attributes, pH,
EC, redox potential, available nutrients (N, P, K, Ca, Mg, S, Al and Na), anions
(chloride, bicarbonate, sulphate and phosphate), exchangeable cations ( Mg, Na, K,
Al, Fe and Mn), percent cation saturation (Ca, Mg, Na and K) and dehydrogenase
activity varied significantly among the three stages of cultivation. The decisivecations identified in the exchange complex of Pokkali soils were potassium and
magnesium, copper and sodium. Sulphate and phosphate were the predominant
anions existing in the soil. Step down regression identified ‘potassium’ having
predictive ability towards the presence of sulphate ion. Higher concentrations of P, K,
Ca, S, Fe, Mn, Zn, Cu, Al and SO42− were observed in the soil. Magnesium was found
to be deficient in the available pool of Pokkali soils. . The plant nutrients namely P,
K, Ca, Mg, Fe, Mn, Cu, Zn, B and Na were significantly varying among three stages
of cultivation. Magnesium was present in higher concentration in plant despite the
deficient concentration of magnesium in soil. The variation in Pokkali rice yield (45
per cent) can be mainly accounted for potassium, calcium, zinc and copper content in
soil at the mound preparation stage. During the harvest stage, yield was correlated
only with available P. Zinc, boron and aluminium were present in toxic
concentrations in plant.
The NIE ratios K/ [(Ca+ Mg+ Fe+ Mn) 1/2 + (Al) 1/3 ] and Na/ [(Ca+ Mg+ Fe+
Mn) 1/2 + (Al) 1/3 ] showed significant positive correlations only with CEC and sodium.
Phosphate showed a strong negative correlation with both the ratios. The other NIE
ratio Mg/ [(Ca+ Mg+ Fe+ Mn) + (Al) 2/3 ] showed significant negative correlation with
pH and phosphate. The ratio Cu/ [(Ca+ Mg+ Fe+ Mn) 1/2 + (Al) 1/3 ] showed a negative
correlation with electrical conductivity, Na and K. The availability of cations namely
K, Mg, Cu and Na was significantly influenced by various soil parameters.
The present investigation identified high concentrations of micronutrients, Al
and B in Pokkali soils, toxic concentrations of Zinc, boron and aluminium in plant
and influence of different soil parameters on availability of K, Mg, Cu and Na. The
rice yield mainly depended on available K, Ca, Zn, P and Zn contents in soil.