Phosphorus sorption by major agricultural soils of Alaska

Surface soils from ten soil series representing five great groups were collected from Alaska. These soils were selected from the important agricultural areas covering a wide geographic distribution. These soils can be divided into two distinct groups based on their parent material: loess and volcanic ash. Phosphorus sorption maxima were calculated based on the Langmuir isotherms. The volcanic ash soils (Cryandept and Cryorthods) showed an average P‐sorption maxima of 10,122 mg/kg and loess soils averaged 3,934 mg/kg. Both groups have similar portions of phosphorus in the organic form (19%) and occluded form (8 to 9%). The nonoccluded‐P in the volcanic ash soils and the loess soils was 68% and 43% respectively, and the Calcium‐P was 4% and 29% respectively. Regression analysis indicated that aluminum and iron are primarily responsible for P‐sorption. The dithionite extractable Al is responsible for P‐sorption in volcanic ash soils, while oxalate extractable Al is responsible for P‐sorption in loess soils. Dithionite and oxalate extractable Fe probably play a secondary role in P‐sorption. The sorption isotherm, regression analysis and the P‐fractionation data provide the agronomist with useful information to estimate P requirement of newly cleared soils.