Modeling Fate and Transport of Nitrogen and Phosphorus in Crop Fields Under Tropical Conditions
Caiado, Marco Aurelio
MetadataShow full item record
Modeling is a very important tool for developing nonpoint source (NPS) pollution control plans. Current NPS models were developed for temperate conditions and, thus, do not appropriately represent tropical conditions. The objective of this research was to develop or adapt a nonpoint source pollution model to simulate transformations and losses of nitrogen (N) and phosphorus (P) in leachate and runoff from crop fields under humid tropical conditions. An extensive literature synthesis identified appropriate relationships for representing hydrologic and NPS processes in the tropics, as well as soil and climate conditions that differ from temperate conditions and impact NPS pollution. The GLEAMS model was selected for adaptation. Changes to the model included calculation of potential evapotranspiration (ET); changes in initial and default values of N and P pools, C:N ratio of soil organic matter, and soil P sorption; changes in simulation of transformations between N and P pools, along with the effect of temperature; and inclusion of a nitrate retardation factor (Ncrit) and pH in the calculation of N transformation and movement. The adapted model, called TROPGLEAMS, was evaluated through model verification, application, and sensitivity analysis. Model verification comprised a mass balance of nutrients and analysis of the variation of variable values in time. Model validation included application of the GLEAMS and TROPGLEAMS to three sites in Brazil: a set of lysimeters planted with sugarcane in Piracicaba, SP; a set of plots planted with sugarcane in Piracicaba; and a set of plots planted in a wheat-soybean rotation in Lages, SC. Model sensitivity to temperature, Ncrit and pH were evaluated in the sensitivity analysis. Model evaluation indicated that TROPGLEAMS is more accurate than GLEAMS in simulating fate and transport of nutrients under tropical conditions. Prediction of actual ET, effect of tillage on losses of N and P in runoff, and N and P kinetics was improved with TROPGLEAMS compared to GLEAMS. However, based on data from the Lages study, TROPGLEAMS did not simulate losses of nutrients in runoff well. Improvements in the model, especially related to losses in runoff, and application of TROPGLEAMS to different areas of the humid tropics are recommended.
- Doctoral Dissertations