Nutrient movement and removal in a switchgrass biomass-filter strip system treated with dairy manure.

Manure use on cropland has raised concern about nutrient contamination of surface and ground waters. Warm-season perennial grasses may be useful in filter strips to trap manure nutrients and as biomass feedstock for nutrient removal. We explored the use of 'Alamo' switchgrass (Panicum virgatum L.) in a biomass production-filter strip system treated with dairy manure. We measured changes in extractable P in the soil, NO3 -N in soil water, and changes in total reactive P and chemical oxygen demand (COD) of runoff water before and after a switchgrass filter strip. Five rates of dairy manure (target rates of 0, 50, 100, 150, and 200 kg N ha(-1) from solid manure in 1995; 0, 75, 150, 300, and 600 kg N ha(-1) from lagoon effluent in 1996 and 1997) were surface-applied to field plots of switchgrass (5.2 by 16.4 m) with a 5.2- by 16.4-m switchgrass filter strip below the manured area. Yield of switchgrass from the manured area increased linearly with increasing manure rate in each year. Soil water samples collected at 46 or 91 cm below the soil surface on 30 dates indicated < 3 mg L(-1) of NO3-N in all plots. Concentrations of total reactive P in surface runoff water were reduced an average of 47% for the 150 kg N rate and 76% for the 600 kg N rate in 1996 and 1997 after passing through the strip. Manure could effectively substitute for inorganic fertilizer in switchgrass biomass production with dual use of the switchgrass as a vegetative filter strip.

Antibiotic choices in surgical intensive care unit patients.

Antibiotics have dramatically changed the care of the critically ill patient over the last 60 years. Patients with complex physiological conditions present with infectious processes requiring the effective use of antimicrobial drugs. In many situations, the inability to eradicate the infectious process is complicated by the progressive development of resistance among the causative organisms. Systemic antibiotic prophylaxis is warranted only for the prevention of wound infections. Regimens in these cases should use large doses of nontoxic antibiotics covering the spectrum of organisms likely to contaminate the wound. The duration of wound prophylaxis should be short, essentially covering only the period of active wound closure; this is usually less than 24 hours. Prevention of most other infections in the ICU depends on the recognition and correction of the various disturbances of host defenses. Topical antibiotic therapy may reduce the level of colonization for a few specific types of infection. Initial empiric antibiotic therapy should be started for clear indications. The antibiotics chosen should be those most likely to be effective against the probable organisms, those which have the lowest toxicity, and those with the smallest likelihood of inducing multiresistance. They must be adjusted promptly based on the microbiologic sensitivities observed. The realization that the physiology of critical illness may alter the normal relations between drug dosages and the tissue antibiotic levels obtained mandates a different approach to the treatment of these patients. The drug volumes of distribution are generally markedly expanded in these patients. Furthermore, these patients require high tissue antibiotic concentrations to improve the chances for successful therapy. Thus, the antibiotics selected must be capable of providing these levels without significant toxicity to the host. Therapy should be continued based on the clinical response observed. Premature cessation of effective therapy often results in relapse.

Determination of Senecio alkaloids by thermospray liquid chromatography/mass spectrometry.

A series of Senecio alkaloid and alkaloid N-oxide standards has been analyzed using positive and negative ion thermospray liquid chromatography/mass spectrometry (LC/MS) with an ammonium acetate-containing mobile phase. On-line separations of pyrrolizidine alkaloids from extracts of Senecio jacobaea (tansy ragwort) and Senecio vulgaris (common groundsel) were done using an ammonium hydroxide-containing mobile phase. All of the alkaloids known to be present in the extracts were detected by ammonium hydroxide thermospray LC/MS, as well as many other components which may be as-yet-unidentified alkaloids.