About Us | Help Videos | Contact Us | Subscriptions



This article in SSSAJ

  1. Vol. 56 No. 6, p. 1967-1973
    Received: July 29, 1991

    * Corresponding author(s):


Soil Test Phosphorus Availability as Affected by Time after Phosphorus Fertilization

  1. A. O. Esilaba,
  2. B. Eghball and
  3. D. H. Sander 
  1. Agricultural Research Dep, Kenya Agricultural Research Institute, Nairobi, Kenya
    Dep. of Agronomy, Keim Hall, Univ. of Nebraska, Lincoln, NE 68583



The availability of fertilizer P in the soil decreases with time after fertilization. Routine soil tests or other estimates of plant-available P should accurately reflect that change. The objective of this study was to determine the effect of the time fertilizer P is in contact with soil on the ability of commonly used soil tests to extract plant-available P. Experiments were conducted to determine the relationship between available P as determined by A value and Bray and Kurtz P1 (BK), sodium bicarbonate (SB), and Mehlich no. 2 (ME) P soil tests. The A value was assumed to be the best available method of determining plant-available P. Samples from an acidic Thurman loamy sand topsoil (sandy, mixed, mesic Udorthentic Haplustoll) and a calcareous Uly silt loam subsoil (fine-silty, mixed, mesic Typic Haplustoll) were incubated with 0, 10, 20, 40, and 80 mg P kg−1 for 4, 8, and 20 mo at field-capacity water content. After each incubation period, oat (Avena sativa L.) was planted and grown in the greenhouse with an additional 0, 10, and 20 mg P kg−1 labeled with 32P. The A value was determined for each incubation period and was correlated with the soil test results. Solubility products were also determined for each incubation P rate and period. After 4 and 8 mo of incubation, the BK, SB, and ME soil tests did not extract plant-available soil P very accurately using the A value as a standard. After 4 mo of incubation, the SB soil test underestimated available P by as much as 50% on the Uly soil, while the BK soil test overestimated available P on the Thurman soil by 40%. Although there was no improvement after 8 mo of incubation, all three soil tests accurately extracted available P after 20 mo when fertilizer P and soil P appeared to have reached an equilibrium. Solubility equilibria analysis lacked adequate sensitivity to show different soil P compounds as affected by time of incubation. The results indicate large potential P fertilizer recommendation errors when soil samples are taken and analyzed prior to achieving equilibrium between applied fertilizer P and soil P.

  Please view the pdf by using the Full Text (PDF) link under 'View' to the left.

Copyright © . Soil Science Society of America