Wednesday, November 7, 2007 - 1:30 PM
244-1

Modeling Bermuda Grass Yield and Quality in the Western San Joaquin Valley of California.

Maximo Alonso and Stephen R. Kaffka. Department of Plant Sciences, University of California at Davis, One Shields Avenue, Davis, CA 95616

We developed a simulation model to predict common Bermuda grass [Cynodon dactylon (L.) Pers.] yield and quality on the saline soils of the western San Joaquin Valley (WSJV), California. The model uses plant, soil and atmospheric variables to estimate crop growth to simulate hay or grazing management. Growth is described by a logistic equation function using potential (maximum) yield (Pot-Yield), the soil nitrogen level (N), and the intrinsic growth rate of the crop (r). Crop growth is restricted by soil salinity using a stress factor (Ks) specific for Bermuda grass: Ks = 1.375 - 0.0625 * ECe. The soil salinity level is estimated through the balance of total dissolved solids (TDS) in the soil, in the irrigation and drainage water, and in the leaching fraction. Crop quality is based on the leaf/stem ratio, which changes with time during each regrowth period and includes neutral-detergent fiber (NDF) and selected mineral contents of the harvested biomass throughout the growing season. The model reasonably simulated Bermuda grass yield and quality in the WSJV. Yield was reduced by salinity levels above 7 dS/m, which were not overcome by increasing soil or fertilizer N. Preliminary results indicate that soil salinity affected grass mineral content but other factors were better correlated with stage of growth that with soil salinity.