Assessment of the AquaCrop-OSPy Model in Simulating Crop-water Productivity in a Corn Field (Sheridan-6 LEMA, Kansas)

Abstract

Unsustainable pumping of groundwater for irrigation purposes has led to aquifer depletion. Over the past decade, groundwater self-governance practices that seek to reduce water use have been established in Kansas and around the world. Simulating the impacts of these water conservation strategies on crop productivity and irrigation requirements may assist in evaluating their effectiveness and impacts. Here, we use the AquaCrop-OSPy model to predict corn yield and irrigation demands under different irrigation strategies over a 20 year period (2000-2020). The study field is located in the Sheridan-6 Local Enhancement Management Area (SD-6 LEMA) established in 2013 to lower groundwater pumping rates. We evaluated the AquaCropOSPy model for accuracy by comparing its results to readily available yield, water use and evapotranspiration (ET) data. Average reported irrigation values (420mm) were similar to AquaCropOSPy (360mm) when irrigation is triggered when soil moisture drops below 80%. Under the same strategy, AquaCropOSPy produced an ET trend similar to those of other reference ET models. However, AquaCropOSPy overestimated yield (13t/ha - 13.5t/ha) while we observed more variability in the USDA-NASS county level yield (10t/ha - 13.5t/ha). This could be due to AquaCropOSPy not accounting for stressors such as pesticides and severe water stress or differences between this field and the county average. Irrigation levels decreased at the onset of the LEMA which could indicate the LEMA’s effectiveness on lowering water use. Future work will calibrate the model to improve simulation performance and expand the domain to northwestern Kansas and south-central Colorado.