Chemical Availability of Native and Applied Phosphorus in Soils and their Textural Fractions1
- R. L. Halstead2
In a study of several Canadian soils, the Al-P fraction (Chang and Jackson, 4) was correlated with the percent yield [(yield without P × 100)/yield with P] of oats grown in the greenhouse and with estimates of available P (NaHCO3-soluble). Although Fe-P was related to NaHCO3-soluble P and Ca-P to acid-soluble P (Troug, 20), neither the Fe- or Ca-P fraction was related to yield. NH4Cl-soluble P, however, was correlated with both percent yield and percent P uptake. The four P fractions (NH4Cl-soluble, Al, Fe, and Ca) comprised a major part (62 to 92%) of the total inorganic P in the soils. Ca-P was the main form in all but the Podzols, in which Fe-P predominated.
Organic P, Al-P, Fe-P, and NaHCO3-soluble P increased with decreasing particle size, whereas Ca-P, total inorganic P, and acid-soluble P (Truog) increased with decreasing particle size in the Podzols but not in the other soils. When the P in the total amount of a given particle-size fraction present in the soil (F value) was considered, it was found that the coarser fractions contributed a relatively large proportion of the P in some of the soils. In five out of seven comparisons a major part (>50%) of the total inorganic P, Ca-P, and Al-P was associated with the coarser silt and sand, whereas Fe-P and organic P were associated with the fine silt and clay. The significant relation of F values for Al-P of the clay to percent yield and percent P uptake provided further evidence of the importance of Al-P as a source of P for plants. Other relationships between yield parameters and F values for NH4Cl-soluble P and Ca-P of the clay indicate that the clay may be a primary source of plant P.
In incubation studies with soils and textural fractions, a major part of the added P was recovered in the Al- and Fe-P forms. Al-P was the primary form of recovery except in the fine silt and clay fractions of the Podzol soils where Fe-P predominated.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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