Search Results

You are looking at 1 - 2 of 2 items for

  • Author or Editor: D. A. Martens x
Clear All Modify Search
Authors: and

The discovery in 1983 of deformities, reproductive failures, and high waterfowl mortality rates at Kesterson National Wildlife Refuge, western San Joaquin Valley, Calif., due to selenium (Se) -contaminated drainage water, raised concerns that these problems may be occurring in the >600 wetlands and National Wildlife Refuges being utilized to collect irrigation drainage waste water in 17 western states. The waterfowl problems were traced to ingestion of organic Se present as Se-amino acids. Plants assimilate soluble Se into Se-amino acids and release them upon decomposition. Aerobic plant residue decomposition studies showed that 50% of the assimilated Se was mineralized to soluble Se, while the remaining organic Se persisted. This means that each growth cycle results in a steady decrease of soluble Se and an increase in organic Se levels. To test the effect of plant growth on Se accumulation, two types of evaporation ponds were evaluated, one with prolific plant growth, and the second relatively devoid of plant growth. Soil Se analysis showed that plant growth dramatically increased Se accumulation in the surface layers. Evaluation of additional Se-contaminated sites showed that Se accumulation followed an exponential function and accumulated rapidly above a 2% soil organic C content. Without plant growth, the Se remains mobile and diffuses to low concentrations in the underlying soil, suggesting that plant residue cycling is an important factor in Se accumulation and toxicity.

Free access
Authors: and

Incorporation of specific vitamins such as thiamin to the rooting media has been reported to stimulate root and shoot growth. Thiamin is involved in the Kreps cycle decarboxylation of pyruvate to citrate as a coenzyme in the pyruvate decarboxylase enzyme complex. Axenic and soil glasshouse studies were conducted to determine the tissue nutrient concentrations (ICP analysis), especially Ca, in response to low application rates of thiamin. In a 50 d axenic “Grand Rapids” lettuce study, thiamin (5 mg mL-1 0.5 N Hoagland's) stimulated shoot length (25%), root length (23%), Ca (8%), K (14%), and P uptake (18%) compared with control values (no thiamin added). Soil glasshouse “Grand Rapids” lettuce studies showed that thiamin (6 mg kg-1 soil) stimulated N (72%), Ca (58%). K (12%), and P uptake (11%) compared with control values. Additional glasshouse-soil-thiamin form studies with “Black seeded Simpson” lettuce (20 mg each form kg-i soil) showed thiamin compounds increased Ca tissue levels from 3 to 10% and organic C content from 5 to 30%. The prospect of using these compounds to reduce tipburn in lettuce is being investigated in follow-up studies.

Free access