AgInput: An Agricultural Nutrient and Pesticide Source Model Peng Wang & Arturo A. Keller Received: 13 June 2007 / Accepted: 21 November 2007 # Springer Science + Business Media B.V. 2007 Abstract Agriculture can be a major nonpoint source (NPS) of nutrient and pesticide contamination in the environment. Available databases do not provide accurate and dynamic data on fertilizer and pesticide application, which limits the ability of complex watershed models to simulate contami- nant loads into impaired water bodies. A model for estimating agricultural nutrient and pesticide input for watershed modeling has been developed. Climate, soils, and major agricultural operations are considered within the model, so that it can be adapted to any watershed or subregion within a watershed. The timing of the agricultural operations is a function of the weather data, providing realistic results at daily, monthly, or annual application rates. The model also predicts irrigation demand and biomass production, which can be used to calibrate the model. Model output can be used in any watershed model that considers agricultural land uses. Two case studies were evaluated, using grape vineyards in the Napa River and strawberry production in Newport Bay as examples. The predicted time to maturity corresponded well with actual data. Irrigation and fertilizer needs were very sensitive to weather input. Although the model can generate weather from long-term averages, the simulated results are best when at least observed precipitation and temperature are provided, to capture extreme events. The model has data for 98 crops and 126 pesticides, based on the California Department of Pesticide Regulation database. The databases are easily modifiable by the user to adapt them to local conditions. The output from AgInput is much needed for watershed modeling and for development of total maximum daily loads (TMDLs), based on realistic targets of irrigation, nutrient, and pesticide inputs. The model is available for free down- load at http://www2.bren.ucsb.edu/~keller/watershed.htm. Keywords TMDL . Nonpoint source . Agricultural source . Fertilizer . Pesticide 1 Background Nutrients are a major source of water quality impairments in the US. EPA reports that nutrient pollution is a leading cause of water quality impairment in lakes and estuaries and is also a significant issue in rivers [19]. Monitoring data from the National Water Quality Assessment Program (NWQAP) found that the highest concentrations of nutrients in streams occur in agricultural basins, and nutrient concentrations in agricultural streams are correlated with nutrient inputs from fertilizers and manure used for crops [20]. According to NWQAP, detection of pesticide com- pounds were widespread in shallow groundwater samples, with one or more pesticide compounds being detected in 54.4% of the 1,034 wells and springs sampled [10]. Although urban pesticide usage has increased significantly in these years, agriculture still remains the major source of pesticide in rivers and lakes. There were 1,238 pesticide- related impairments in the 2002 303(d) list [19]. Thus, agriculture is a major nonpoint source (NPS) of nutrient and pesticide contamination in the environment. Section 303(d) of the Clean Water Act (CWA) requires that “states, territories and authorized tribes are to list waters as impaired for which technological-based limits alone do not ensure attainment of water quality standards and to Environ Model Assess DOI 10.1007/s10666-007-9133-3 P. Wang : A. A. Keller (*) Bren School of Environmental Science and Management, University of California, Santa Barbara, CA 93106, USA e-mail: keller@bren.ucsb.edu