Tuesday, November 14, 2006

A Wheat Grazing Model for Simulating Grain and Beef Production in the US Southern Great Plains.

Xun-Chang Zhang1, W.A. Phillips2, J.D. Garbrecht2, J.L. Steiner2, and L.T. Hunt3. (1) USDA-ARS, USDA-ARS Grazinglands Res. Lab., 7207 W. Cheyenne St., El Reno, OK 73036, (2) USDA-ARS Grazinglands Res Lab, 7207 W. Cheyenne St, El Reno, OK 73036, (3) Univ. of Guelph, Dep of Plant Agr., Guelph, ON N1G 2w1, Canada

It is a common practice to raise winter wheat (Triticum aestivum L.) as a dual-purpose crop in the U.S. Southern Great Plains due to the added value by cattle production.  For example, nearly one million hectares of winter wheat were grazed in Oklahoma in 2000.  Management of the dual-purpose wheat is complex because of the complicated interactions and tradeoffs between grain and beef production.  A wheat grazing model will be of great use in optimizing management options.  The objectives are to develop a metabolizable energy-based cattle growth module and to incorporate it into the latest DSSAT model for simulating production of wheat grain and stocker cattle grazing on wheat during late fall and early spring for the U.S. Southern Great Plains.  The wheat grazing model has three components: wheat growth, cattle growth, and wheat-cattle interface.  Wheat growth is simulated by the wheat module of Decision Support Systems for Agrotechnology Transfer (DSSAT).  Cattle growth is based on metabolizable energy balance.  For wheat-cattle interface, individual leave areas, as well as leave, stem, and reserve weights and their corresponding N contents are adjusted for grazing on a daily basis.  The model will be evaluated using experimental data of wheat growth and cattle weight gain collected in El Reno, Oklahoma.