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Quantifying Field Water Balance Components as Affected by Shifts in Land-Use Patterns: Implications for Minimizing Agricultural Impacts on Water Quality in Iowa
YEAR: 2012
INVESTIGATORS: Robert Horton, Matthew Helmers

Increasing energy demands, global warming and concerns about fossil fuel depletion has led to an increasing focus being placed on bioenergy crops in the US. Large scale land-use changes from a corn-soybean rotation to native perennial plants have the potential to significantly alter the regional water balance and nutrient dynamics in the Midwest region of the US. Since nutrient loads in the surface water bodies remain a major environmental problem in Iowa today, it is vital to understand how the shift in land-use patterns can affect the regional hydrological cycle and change nutrient transport processes. In earlier research carried out by the PI and collaborators at the Comparison of Biofuel Systems (COBS) research site near Ames, IA, significant differences were observed in the drainage volumes and drainage water quality parameters among different biofuel cropping systems. The mechanisms driving these differences remain largely unknown. Crop evapotranspiration (ET) is a dominant factor in water balance of any region, but data are not available for direct field measurements of ET for some field crops, especially for a mixed prairie stand. There is a need to quantify ET by direct field measurements to help quantify the regional hydrological cycles. It is also important to quantify how changes in cropping systems affect the regional patterns in order to improve the management of regional water quality problems. The goal of the proposed work is to quantify the field water balance components as affected by different biofuel cropping systems. Direct field measurements of ET by a chamber technique and by sap flow measurements coupled with soil moisture, drainage and water quality data will enable us to measure crop water use under different cropping systems. This will also help us to quantify the dominant components leading to differences in drainage volumes among different cropping systems. The data obtained will be used to evaluate a crop growth, hydrological, and water quality model (RZWQM) to provide a tool for investigating the implications of land-use changes on field, state, and regional hydrological scales under a variety of soil, climatic and cropping conditions.