WATER EFFECTS ON GUAYULE RUBBER PRODUCTION.

Guayule Parthenium argentatum Gray was transplanted in April and October 1980 near Litchfield Park, west of Phoenix, AZ. Four irrigation application depths were applied to plots in a randomized block design. Shrubs were harvested in June 1982, winter 1982-83, and January 1984. Dry matter produced, rubber content, and rubber yield were determined. Dry matter production increased with increasing water. Rubber content decreased with increasing water. Rubber yield showed a slight increase with increasing water. Estimated production costs show guayule is not economical to produce at current rubber prices. For the growing conditions at the site, 500 mm of irrigation water application annually would be most economical but more costly than guayule grown under better soil conditions.