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Agronomy Journal Abstract -

Evaluation of the EPIC Simulation Model Using a Dryland Wheat-Sorghum-Fallow Crop Rotation1


This article in AJ

  1. Vol. 79 No. 4, p. 732-738
    Received: July 15, 1986

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  1. J. L. Steiner,
  2. J. R. Williams and
  3. O. R. Jones2



Dryland cropping is extremely variable, and stability over time is important. Analysis of soil-crop-climate interactions using simulation models can expand dryland cropping research through extrapolation of experimental results across a range of soils, climates, and management practices and over longer time periods. The Erosion-Productivity Impact Calculator (EPIC) simulates evapotranspiration (ET), runoff, plant growth, and related processes; but validation was needed for semiarid regions. Predicted ET, runoff, soil water, and crop yield were compared to data collected from 1958 to 1984 at Bushland, TX. Wheat (Triticum aestivum L.) and sorghum [Sorghum bicolor (L.) Moench] were grown on a Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll), with each crop grown each year. Predicted mean growing season ET, soil water depletion, and annual runoff were not significantly different from observed values. EPIC tended to underpredict high values of water balance components and overpredict low values, but predicted realistic distributions of values. Local calibration of the conversion factor of dry matter production from intercepted radiation was required for yield prediction of 1.3 and 2.7 Mg/ha for wheat and sorghum, respectively, which then did not significantly differ from observed values of 1.3 and 2.3 Mg/ha. EPIC was generally satisfactory in predicting the water balance over long periods of time, with means, standard errors, ranges, and probability distributions being similar for observed and predicted values. Satisfactory yield prediction required calibration to the location. Prediction of yield or water balance components for specific fields in specific years is not recommended.

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