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Simulating Winter Wheat Production in Three Tillage Systems Using the Nitrogen Tillage Residue Management Model

Dep. of Water Resources, Office of Water Conservation, Sacramento, CA 94236-0001
USDA-ARS, Dep. of Agronomy, Univ, of Nebraska,, Lincoln, NE 68583-0915.
Dep. of Agronomy, Univ. of Nebraska, Lincoln, NE 68583-0915.

^* Corresponding author.

Crop production system analysis is necessary to identify tillage and residue management practices that affect crop production. The objective of this study was to evaluate the potential of using the Nitrogen Tillage Residue Management (NTRM) model to evaluate the influence of tillage practices on winter wheat (Triticum aestivum L.) yield. Modifications of the NTRM model were required to simulate winter wheat production. The model was calibrated using site-specific information obtained from a tillage-nitrogen rate experiment conducted at the High Plains Agricultural Laboratory near Sidney, NE, on an Alliance silt loam (fine silty, mixed, mesic Aridic Argiustoll). Model output was compared to measured yields of winter wheat grown on three tillage treatments [moldboard plow, subsurface tillage (1.5 in-wide "V" blade), and no tillage] during three seasons. Simulations within the year of calibration agreed within ± 28% of measured yields for the moldboard plow and subsurface tillage treatments. Deviations were observed between predicted and measured yields when using data outside the year of calibration. Crop coefficients, determined in the calibration process, affected the yield predictions of NTRM. Grain yield predictions by NTRM were very sensitive to initial and stabilized soil bulk density values within the range of 1.2 to 1.3 Mg m^–3 (1% change in input value caused a five-fold change in predicted yield). Usefulness of the model could be enhanced through greater documentation on calibration procedures and explanation of calibration coefficients. Results obtained here should alert users to the need for care in application of results obtained from complex, highly interlinked models, such as NTRM.

Received for publication May 4, 1990.