NUTRIENT REQUIREMENTS OF CHAMAEROPS HUMILIS L. AND WASHINGTONIA ROBUSTA H. WENDL PALM TREES AND THEIR LONG-TERM NUTRITIONAL RESPONSES TO SALINITY

The ornamental value of plants used in semiarid areas can be improved by knowledge of their required nutrients and of their nutritional responses under saline conditions. We present a long-term study concerning the nutritional status in Chamaerops humilis and Washingtonia robusta. Two-year-old plants were grown for two years outdoors in pots using water with electrical conductivity values of 2 (control) or 8 dS m^?1 (saline conditions). Nutrient specific absorption rates and leaf nutrient transport rates were estimated by fitting a Richards function regression. We suggest fertilizing C. humilis and W. robusta plants with nitrogen (N): phosphorus pentoxide (P₂O₅): dipotassium oxide (K₂O) ratios of 4:1:5 and 5:1:3, respectively. Diagnosis and Recommendation Integrated System (DRIS) and Plant Analysis with Standardized Scores (PASS) norms were also evaluated. PASS norms provided better nutritional diagnosis than DRIS norms. In saline conditions, PASS-INI (Independent nutrient index) pointed to a deficiency (C. humilis and of nitrogen in W. robusta.