Developing and evaluating a phosphorus (P) module in RZWQM2 for phosphorus management in tile drained agricultural fields

Abstract. Phosphorus (P) applied in agricultural fields in terms of manure and fertilizer is lost through surface runoff and tile drainage while the tile drainage contributes more towards this loss in some regions of CANADA and USA. This lost phosphorus from the agricultural fields eventually reaches to water bodies causing widespread P pollution and eutrophication due to algal blooms. However, as of present day, there is lack of models which can simulate P loss from tile drained agricultural field. Therefore, in this research an effort is undertaken to develop a model-based P management tool in tile drained fields although it can be used naturally drained field. The developed P model is based on the most recent scientific findings regarding the fate and transport of P and uses the output of hydrology and crop growth from RZWQM2, an agricultural system model. The developed P model is designated in simulating both dissolved reactive phosphorus (DRP) and particulate phosphorus (PP) loss through surface runoff and tile drainage while special attention has been paid to simulation of P loss through tile drainage. The developed P model is tested in simulating P losses (DRP and PP) through surface runoff and tile drainage in a tile drained corn-soybean field located near Harrow, Ontario from June 2008 to May 2012. Measured DRP and PP loss through both runoff and tile drainage in regular drainage plots treated with inorganic P fertilizer is used to calibrate and validate the model. The test results reveal that the developed P model is capable of simulating DRP and PP losses through both surface runoff and tile drainage satisfactorily with Nash-Sutcliffe model efficiency (NSE) >0.5 ,percent bias (PBAIS) within ± 0.25 and Index of Agreement (IoA) > 0.75 in both calibration and validation period.