Nitrogen release from roots of alfalfa and soybean grown in sand culture |
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Authors: | Laura S Brophy G H Heichel |
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Institution: | (1) Department of Agronomy and Plant Genetics and USDA-ARS, Department of Agronomy and Plant Genetics, University of Minnesota, 1991 Upper Buford Circle, 55108 St. Paul, MN, USA;(2) Present address: Department of Botany and Plant Pathology, Oregon State University, 97331-2902 Corvallis, OR, USA |
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Abstract: | An enclosed root chamber containing sterile sand medium was used to study net nitrogen (N) release from actively growing root
systems of ‘Saranac’ alfalfa (Medicago sativa L.) and ‘Fiskeby V’ soybean (Glycine max L. Merr.). Plants were inoculated with a rhizobial strain appropriate to each host, irrigated with N-free nutrient solution,
and grown either to 85 or to 173 d after germination (alfalfa) or to physiological maturity (soybean). Alfalfa released 4.5%
of symbiotically-fixed plant N into the root zone over its growth period; soybean released 10.4% of plant N. Root zone leachates
were analyzed for total N and for amino acid and ammonium content. Significant ammonium-N release occurred from the alfalfa
but not the soybean root system; little amino-N was released by root systems of either species. Shoot harvest and water deficit
caused increased release of N from alfalfa roots. The results provide evidence that alfalfa and soybean released significant
proportions of their N into the root zone, and indicate that while substantial ammonium-N was released from alfalfa roots,
passive leakage of amino-N was not a primary mechanism for N release from root systems of either species.
Cooperative investigation of USDA-ARS and the Minnesota Agric. Exp. Stn. (Scientific J. Series No. 16048). This research was
supported in part by a Graduate School Fellowship to LSB from the Univ. of Minnesota. |
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Keywords: | alfalfa amino acids ammonium Glycine max (L ) Merr leachates lucerne Medicago sativa L nitrogen rhizosphere root exudates soyabean |
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