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This article in SSSAJ

  1. Vol. 56 No. 5, p. 1510-1515
     
    Received: Aug 8, 1990


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doi:10.2136/sssaj1992.03615995005600050029x

Phosphorus Fractions and Availability in Sri Lankan Alfisols

  1. R. R. Sattell and
  2. R. A. Morris 
  1. Dep. of Crop and Soil Science, Oregon State Univ., Corvallis, OR 97331-7306

Abstract

Abstract

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 NaHCO3) 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 (NaHCO3-Pi) and moderately labile organic (NaOH-Po) fractions. Double-acid P (extracted with 0.5 M HCl plus 0.0125 M H2SO4) 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.

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