Validation of a Simple Rye Growth Model Against Published Field Studies and RZWQM.

The role of fall-planted winter cover crops in soil and water resource management is increasing, given current emphases of improving water quality, conserving soil, and producing biomass for energy without reducing food production.  Although numerous cover crop field studies have been published, estimating effectiveness of cover crops across a large region such as the U.S. corn-soybean belt is challenging given variability such as weather and soil.  Simulation modeling provides a method to assess cover cropping uncertainties within a shorter timeframe and with a fraction of resources required for field experimentation.  Our objective was to  test the winter cover crop simulation model RyeGro with published spring biomass accumulation from field studies. RyeGro is a simple radiation use efficiency model developed for use in the Northern Corn Belt.  We obtained input and output data for 44 site-years of model simulations from Midwest and Mid-Atlantic locations.  RyeGro’s original Minnesota calibration values were used.  RyeGro underpredicted spring biomass accumulation by 13% for Midwest locations (3.1 vs. 3.5 Mg/ha), with a mean absolute error (MAE) of 1.3 Mg/ha.  Results from Mid-Atlantic locations were poor, with RyeGro overpredicting biomass accumulation by 64% (8.5 vs. 5.2 Mg/ha), with an MAE of 4.4 Mg/ha.  In addition to comparing RyeGro performance with field studies, we will further compare outputs with the detailed, process-based Root Zone Water Quality Model.