Field-scale calibration of crop-yield parameters in the Soil and Water Assessment Tool (SWAT)

Abstract: Accurate modeling of crop growth within watershed hydrological models is essential, yet most stud-ies pay little attention to parameterizing crop-growth sub-models or validating their performance. Thisstudy evaluated crop sub-model parameters of Soil and Water Assessment Tool (SWAT), a widely used,physically based, hydrological model. Baseline SWAT crop parameters were calibrated at the modelhydrologic-response-unit-scale using 10 years of replicated field-scale data at one site and validatedusing 5 years at a second site for corn and grain sorghum, and new parameters were developed andtested for sweet sorghum (bioenergy crop) using 4 years of unreplicated field data. Calibration of cropyields focused on four parameters: lower harvest index (WYSF), harvest index for optimal growing condi-tion (HVSTI), radiation use efficiency (BIO E), and maximum leaf area index (BLAI). Calibration improvedmodel performance and resulted in slight changes to SWAT default values for four parameters for cornand sorghum. These results provide important preliminary parameters for modeling sweet sorghum inSWAT; both BIO E and BLAI were greater than default values for grain sorghum. Calibrated parametersimproved model performance in validation of corn but not grain sorghum, which was heavily influencedby drought conditions and possibly other management differences at the validation site. Results of thisstudy support use of site-specific, rather than default or off-site, calibration of crop-model parametersto minimize effects on model performance of different soil, water, and nutrient management conditions.Watershed-specific, field-scale crop-yield calibration methods demonstrated in this study are recom-mended to reduce the plant-growth-related systematic error component of larger-scale hydrologicalprocesses (such as streamflow).

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