|Magarian, D - UNIVERSITY OF MINNESOTA|
|Blumenthal, J - UNIVERSITY OF MINNESOTA|
Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: June 25, 1995
Publication Date: N/A
Technical Abstract: The 15N isotope method is a reliable way to measure NO3-N uptake in N2-fixing legumes but is too expensive for plant breeding programs. Bromide is used to mimic NO3 movement in soils and is inexpensive to analyze. We tested whether Br reflected actual NO3 uptake in nodulated alfalfa (Medicago sativa L.). The variety 'Webfoot' was grown in soil for 28 wk in the greenhouse. After clipping herbage to 5 cm, daily additions of solutions containing Br and 15N-labeled NO3 were made. Regrowth accumulated over 15, 25, and 35 d was analyzed for the two tracers. At a constant [NO3] (5 mmol N/L), but varying [Br] (0.04 to 50 mg/L), the ratio of the two tracers in the herbage reflected solution ratios. At constant nitrate:Br ratio, but varying concentrations, tracer ratios in the herbage were constant, except for the highest [NO3] (20 mmol N/L) and in 35-d-old tissue (full bloom). In 96 35-day-old individual plants, tracer ratio was normally distributed but had a CV of 20%. Our results support the idea that Br can be used to select N2-fixing plants for NO3 absorption until early reproductive growth stages.