Changes in extractable phosphorus in Alberta soils during the fall‐winter‐spring interlude

Abstract

Abstract Extractable P values have been assumed to be similar whether soil samples are taken in fall or spring. The objectives of the present study were to determine if extractable P values change over the fall‐winter‐spring interval and whether similar trends are observed using different extractants. Three sites in north‐central Alberta (one each of Black Chernozem, Dark Gray Chernozem and Gray Luvisol) were sampled several times in the period September to late April. Three extractants were: 0.03M. NH4F + 0.015M H2SO4 solution; 0.5M NaHCO3 solution (pH 8.5), and distilled water. The amount of extractable P varied with the sampling time and the extractant. Extractable P increased to a similar degree for all extradants from early to late fall sampling and through the frozen soil period, but the values decreased at the spring sampling after soil had thawed. These results have major implications for fertilizer P recommendations based on soil samples taken at different times.