Repeated Bray-2 extractions of an Inceptisol and an Andisol
Title:
Repeated Bray-2 extractions of an Inceptisol and an Andisol
Author:
Takahashi, Shigeru
Appeared in:
Communications in soil science and plant analysis
Paging:
Volume 30 (1999) nr. 3-4 pages 535-543
Year:
1999-02
Contents:
Bray-2 extractable phosphorus (Bray2-P) is commonly used to measure plant-available P in soil. The pool size of extractable P in the residual soil should be reduced after extraction. Phosphorus, once released with the Bray-2 solution, is resorbed by the soil during the extraction-filtration period. If P resorption is large, the Bray2-P concentration is underestimated. The P absorption coefficient and composition of inorganic P [calcium (Ca)-P, aluminum (Al)-P, and iron (Fe)-P] probably affect the Bray2-P concentration. We investigated the effect of repeated Bray-2 extractions on the Bray2-P concentrations in relation to the P absorption coefficient and Ca-P, Al-P, and Fe-P concentrations in two soils (an Inceptisol and an Andisol), which markedly differ in the P absorption coefficient. Test soil samples were the initial soil (S0) and soils after the 1st to 4th extractions (S1-S4) for the Inceptisol, and S0, S1-S4, and S7 for the Andisol. The Bray2-P, Ca-P, Al-P, and Fe-P concentrations in the S0 were 260, 75, 338, and 536 mg kg-1 in the Inceptisol, and 217, 31, 972, and 354 mg kg-1 in the Andisol, respectively. All of the extractable P concentrations in the Inceptisol decreased with increasing numbers of extractions, and the Bray2-P, Ca-P, Al-P, and Fe-P concentrations in the S4 were 5.3, 21, 5.7, and 30% of those in the S0, respectively. On the other hand in the Andisol, the Bray2-P, Ca-P, and Fe-P concentrations did not decrease in the S1 and S2 compared with those in the S0, although the Al-P concentration decreased with increasing numbers of extractions. The Bray2-P, Ca-P, Al-P, and Fe-P concentrations in the S7 were 23, 71, 16, and 79% of those in the S0, respectively. The P absorption coefficient in the S0 was higher in the Andisol (7,703 mg kg-1) than in the Inceptisol (1,582 mg kg-1), and it decreased with increasing numbers of extractions in both soils. The P absorption coefficient in the S7 Andisol was 51% of that in the S0, while the P absorption coefficient in the S4 Inceptisol was 24% of that in the S0. The results suggest that Presorption affects the efficiency of extraction with the Bray-2 solution, and the composition of Ca-P, Al-P, and Fe-P fractions. The Bray2-P concentration in soil with high P absorption coefficient is underestimated due to P resorption.
Journal description