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