Simulating grass productivity on diverse range sites in Texas

ABSTRACT:

Simulation models addressing soil erosion and water quality issues on range sites should realistically simulate grass dry matter yields across a wide diversity of soils and climate regimes. This study was designed to evaluate the ability of the ALMANAC (Agricultural Land Management Alternatives with Numerical Assessment Criteria) model to simulate annual range grass biomass production under diverse climatic conditions and soils in Texas. The objective was to compare range grass production at rangeland ecological sites, as reported in the U.S. Department of Agriculture Natural Resources Conservation Service ((USDA NRCS) soil surveys, with production simulated by ALMANAC using the most common grasses for each site. The model was run with 60 years of daily weather data on 20 different soils from a diverse set of sites in Texas. The weather data was from seven sites. Model inputs included parameters for the soil series, grass species characteristics, and locally measured climate data. After allowing 10 years for the model to equilibrate, means for simulated production for the sites for the next 50 years were similar to reported means. Simulated production in high rainfall years and low rainfall years were also similar to reported values. The soils, climate, and grass parameter data sets developed here can be useful starting points for deriving data for additional range sites, giving model users examples of realistic input data. The model shows promise as a tool for realistically simulating grass production on a diverse group of soils and in diverse climatic conditions.