Soil Sampling Methods for Phosphorus – Spatial Concerns

Purpose of This Publication Knowledge of soil phosphorus (P) levels is an essential component of nutrient management planning for crop production and for tools that assess the risk of P loss from agricultural fields. Historically, soil P testing has been used to estimate P availability for crops and is now being used directly or as a component of P indices to assess the risk of P loss from fields to water resources. A basic assumption of soil testing for crop production is that the soil sample collected represents a certain area with an acceptable margin of error. Therefore, appropriate soil sampling methods are needed for effective agronomic P management and environmental P assessment. A recent SERA-17 position paper (Vadas et al., 2006) addressed the issue of soil sampling depth. This position paper summarizes important practical aspects of topsoil P variability (within 20 cm depth) across the landscape with an emphasis on within-field variability, and sampling methods that have been recommended or proposed to assess soil P and suggests practical soil sampling options for agronomic and environmental purposes.