Storage‐Induced Changes in Phosphorus Solubility of Air‐Dried Soils

Soil is commonly stored in an air‐dried state for extended periods before chemical analysis. The effect of storage on P solubility was assessed by determining NaHCO 3 –extractable P concentrations in a range of pasture soils from England and Wales (total C = 28.9–80.4 g kg −1 , clay = 219–681 g kg −1 , pH = 4.4–6.8) immediately following air drying and after 3 yr of storage at ambient laboratory temperature. Following storage, NaHCO 3 –extractable inorganic P concentrations decreased by between 2 and 60% (mean decrease = 21%), while NaHCO 3 –extractable organic P concentrations increased by between 48 and 156% (mean increase = 95%). The greatest changes occurred in soils of pH < 5.3. The changes appear to result from the disruption of organic matter coatings on mineral surfaces, continuous solid‐phase diffusion of phosphate into soil particles, and decomposition of microbial cells. The results have important implications for the determination of NaHCO 3 –extractable P in stored soils and highlight the importance of working with fresh samples to derive information with relevance to field conditions.