LOGANATHAN, P & BALAKRISHNAMURTI, TS 1980, 'EFFECTS OF NPK FERTILIZERS ON YOUNG COCONUT (COCOS-NUCIFERA) ON A SANDY SOIL IN SRI-LANKA', EXPERIMENTAL AGRICULTURE, vol. 16, no. 1, pp. 41-48.
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In a 4 × 4 × 4 NPK field experiment with coconut on a sandy soil, N increased girth, height and leaf production during the pre-bearing period, but phosphorus (up to 6½ years) and K (up to 3½ years) had no effect on any vegetative growth parameters. The rates of fertilizers for optimum copra and nut yield (13 to 16 years) were 0.35, 0.73 and 0.64 kg N, PO and KO/palm/ year respectively. The high P requirement was due to the low solubility of the saphos phosphate in these sandy soils. A positive N × P interaction was also observed. © 1980, Cambridge University Press. All rights reserved.
LOGANATHAN, P & FERNANDO, WT 1980, 'PHOSPHORUS SORPTION BY SOME COCONUT-GROWING ACID SOILS OF SRI-LANKA AND ITS RELATIONSHIP TO SELECTED SOIL PROPERTIES', JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, vol. 31, no. 7, pp. 709-717.
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Phosphorus (P) sorption in the presence of 10−2M calcium chloride by ten coconut‐growing acid soil samples of Sri Lanka belonging to the Ultisol, Alfisol and Entisol orders was evaluated using the Langmuir sorption isotherm. The data for all samples fitted the single‐site Langmuir sorption isotherm when equilibrium P was less than 1 μg ml−1, but showed some deviations at larger concentrations of P. A two‐site Langmuir sorption isotherm was successfully used to describe the sorption data of three samples at these high concentrations. The single‐site Langmuir sorption maxima were greater for Ultisols (349–825 μg g−1) than for the other soils (136–345 μg g−1). These sorption maxima were significantly correlated with %‐clay, %‐silt, dithionite‐extractable iron, and 1M ammonium acetate (pH 4.8)‐extractable aluminium. Regression analysis of P sorption on different forms of iron (Fe) and aluminium (Al) indicated that crystalline ‘free Fe oxides’ (dithionite‐extractable Fe minus 0.3M oxalate‐extractable Fe) and ‘active Al’ which consists of hydroxy Al monomers and polymers [1M ammonium acetates, (pH 4.8)‐extractable Al minus 1M potassium chloride extractable Al] were the important factors contributing towards P sorption. Copyright © 1980 John Wiley & Sons, Ltd