Estimating Rates of Soil Phosphorus Drawdown Using the Aple Model.

Many agricultural regions throughout the world have soils phosphorus (P) contents in excess of agronomic needs due to a long history of manure or fertilizer P applications. These regions often have surface water quality problems from P transfer from soils to local water bodies. Recent research has demonstrated that despite conservation efforts, water quality issues may continue well into the future because P enriched soils may continue to lose P at environmentally harmful rates for many years. It is helpful to policy makers to know how many years it may take to reduce soil P contents to agronomic levels though cessation of P applications and crop removal of P. Several long-term field trials have been conducted to provide time estimates, but these studies require 10-20 years to provide information that is needed much faster than that. Modeling tools that can reliably estimate rates of soil P drawdown and associated reductions in P loss can therefore be quite valuable. We demonstrate that the Annual P Loss Estimator (APLE), which is user-friendly, spreadsheet model, can be used to rapidly assess rates of soil P drawdown and P loss for a wide range of soil types and management scenarios.