TY - JOUR T1 - Predictors of feld-scale variation of soil phosphorus JF - Journal of Soil and Water Conservation SP - 153A LP - 153A VL - 62 IS - 6 AU - Sheilah C. Nolan AU - Joanne L. Little AU - Janna P. Casson AU - Frank J. Hecker AU - Barry M. Olson Y1 - 2007/11/01 UR - http://www.jswconline.org/content/62/6/153A.abstract N2 - Predictions of phosphorus loss from agricultural soils can be affected by field-scale variation in soil-test phosphorus (STP) and the degree of soil phosphorus saturation (DPS). Concentrations of soil phosphorus have been shown to vary significantly within farm fields due to factors such as differential management and redistribution by erosion. The relationship between phosphorus in soil and in runoff is further complicated by observations that different areas of a landscape contribute unequally to runoff. Since the zone of interaction with runoff is often limited to the top few centimeters of soil, variations in soil phosphorus by depth of soil layer may also affect predictions of runoff phosphorus. The use of traditional agronomic soil sampling methods may not adequately represent the soil phosphorus pool that is susceptible to runoff. The objectives of our study were to characterize field-scale variations of STP and DPS and relate these to topographic characteristics within eight small watersheds developed on glaciated landforms in Alberta, Canada. An ungrazed grassland site (2 ha [5 ac]) and seven cultivated sites (22 to 248 ha [54 to 613 ac]) represented a range of tillage and manured conditions. Soils were sampled by landform position (upper, mid, and lower) using … ER -