Alfalfa (Medicago sativa L.) survival is dependant on balanced P and K nutrition.  Reactive oxygen intermediates are elevated in plant tissues under abiotic stresses including temperature and nutrient deprivation.  Our objective was to determine how activities of enzymes associated with oxidative stress and lipid peroxidation in alfalfa taproots are altered by P and K nutrition.  Taproot samples were collected in May and early December from field plots receiving contrasting rates of P and K fertilizer.  Extensive plant death occurred in some plots fertilized with P but not K, while survival was excellent in plots fertilized with both K and P or in plants left unfertilized.  Specific activities of superoxide dismutase (SOD) and enzymes associated with the ascorbate-glutathione cycle and the glutathione peroxidase (GPX) cycle increase in taproots sampled in December when compared to those sampled in May.  Changes in SOD and GPX isozyme patterns will be examined using native PAGE to determine if activities of specific isozymes are associated with altered enzyme activation and plant survival.