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Phosphorus Fractions and Availability in Sri Lankan Alfisols
Author(s) -
Sattell R. R.,
Morris R. A.
Publication year - 1992
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1992.03615995005600050029x
Subject(s) - chemistry , phosphorus , alfisol , fraction (chemistry) , setaria , soil water , limiting , environmental chemistry , agronomy , zoology , biology , chromatography , organic chemistry , mechanical engineering , ecology , engineering
Phosphorus is the second most limiting element in the Alfisols of tropical Asia and Africa. The relationships between P fractions in 12 Sri Lankan Alfisols and P taken up by plants in a greenhouse experiment and P removed by five chemical extractants were examined. Soils were selected to represent different land uses and catena positions. Sufficient P to elevate soil solution concentrations to 0.2 µg P g −1 was applied to one set of samples. A second set received 75% of the P applied to the first and a third received no P. Phosphorus uptake by foxtail millet [ Setaria italica (L.)] was determined after 25 d of growth in a Neubauer experiment. Soil P was fractionated sequentially into labile (removed by 0.5 M NaHCO 3 ) and moderately labile (removed by 0.1 M NaOH) inorganic and organic P as well as more stable soil P components. On average, 45% of total soil P was in the NaOH fraction and, of this, 72% was in an organic form. Plant P was significantly related to labile inorganic (NaHCO 3 ‐P i ) and moderately labile organic (NaOH‐P o ) fractions. Double‐acid P (extracted with 0.5 M HCl plus 0.0125 M H 2 SO 4 ) was significantly related to the same fractions. Moreover, double‐acid P was better correlated with plant P than was P removed by those extractants highly correlated only with labile inorganic P. The study suggested that the moderately labile organic P fraction as well as the labile inorganic P fraction contributed significantly to P uptake from tropical Alfisols and that the double‐acid extractant was superior to soil P extractants that are uncorrelated to the moderately labile organic P fraction.