Ion interactions and rice nutrition in acid saline pokkali soils
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Date
2016
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Department of Soil Science and Agricultural Chemistry,College of Horticulture, Vellanikkara
Abstract
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.
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