DRAINMOD-P: A MODEL FOR SIMULATING PHOSPHORUS DYNAMICS AND TRANSPORT IN DRAINED AGRICULTURAL LANDS: I. MODEL DEVELOPMENT

High phosphorus (P) loads to streams and lakes can promote harmful algae blooms and cause water quality deterioration. Recent research has identified subsurface drainage as an important pathway for the transport of dissolved P from drained croplands to receiving surface water bodies, particularly when macropore flow contributes a considerable portion of the subsurface drainage outflow. Currently, a few models are capable of simulating P dynamics in poorly drained soils with artificial drainage systems. The objective of this study was to develop DRAINMOD-P, a field-scale, process-based model that simulates P cycling and transport in drained croplands. Processes represented in the model include atmospheric deposition, organic and inorganic fertilizer applications, plant uptake, sediment-bound and dissolved P losses in both surface runoff and subsurface drainage, tillage practices, and P mineralization and immobilization. The model predicts P losses under different management practices, climatic conditions, drainage systems, and crop rotations. The model is an extension to the nitrogen model DRAINMOD-NII, with full integration of the nitrogen and P model components. DRAINMOD-P uses the recently modified hydrology component that simulates macropore flow. A soil erosion component, based on the RUSLE approach, has been incorporated into the model to estimate sediment loss and associated particulate P loss. Sediment deposition in tile drains is considered to quantify particulate P settling in the drainage system. In this article, we review the approaches used in DRAINMOD-P for simulating P-related processes. Model testing against field-measured data from a subsurface-drained field in northwest Ohio is presented in a companion article.

Automated summary

The study developed the DRAINMOD-P model to simulate phosphorus cycling and transport in drained croplands, predicting P losses under different management practices. The model includes processes such as atmospheric deposition, fertilizer application, plant uptake, and P losses in surface runoff and subsurface drainage.