Predicting Soil Nitratenitrogen Losses From Incorporated Poultry Manure Using the Gleams Model

Proper calibration and validation of computer models can inexpensively and quickly assess the impacts of differentagricultural management practices on water quality. This study used Groundwater Loading Effects of AgriculturalManagement Systems (GLEAMS) version 2.1 to determine the effects of two nitrogen (N) application rates (168 kg N/ha(168PM) and 336 kg N/ha (336PM)) from poultry manure and one N application rate (168 kg N/ha (168UAN)) from ureaammonium nitrate (UAN) fertilizer on NO3N loss with subsurface drainage. The simulated NO3N losses by the GLEAMSmodel were compared with twoyear (1999 and 2000) monthly measured NO3N losses from six 2.1m 2 field lysimeters undercontinuous corn production. Results indicated that the twoyear average simulated subsurface drainage consistently followed the average measuredsubsurface drainage from 168UAN, 168PM, and 336PM treatments, with mean errors of 9%, 3%, and 2%, respectively. Themodel was capable of predicting overall NO3N concentration in subsurface drainage from lysimeters under 168UAN,168PM, and 336PM treatments reasonably well, giving mean errors of 19%, 29%, and 9%, respectively. The overalltwoyear results also show that there were no significant differences (p= 0.05) between average measured and simulatedNO3N losses with subsurface drainage from poultry manure treatments. The study concluded that the GLEAMS model canbe used as a viable management and decisionmaking tool to assess the impacts of longterm poultry manure applicationon water quality and agricultural production for Iowa soils.