Subsoil Nitrate and Bromide Uptake by Contrasting Alfalfa Entries

Autor: JoAnn F. S. Lamb, Michael P. Russelle, Jürg M. Blumenthal
Rok vydání: 1999
Předmět:
Zdroj: Agronomy Journal. 91:269-275
ISSN: 1435-0645
0002-1962
DOI: 10.2134/agronj1999.00021962009100020015x
Popis: Alfalfa (Medicago sativa L.) is a deeply rooted perennial legume that can protect the environment by absorbing nitrate (NO 3 - ) both better than annual crops and from deeper in the soil. Our objectives were to characterize subsoil NO 3 - removal by eight alfalfa entries differing in symbiotic efficiency, root system architecture, forage quality, and leaf morphology, and to evaluate Br - as an alternative tracer to 15 N for monitoring NO 3 - uptake. Low (0.3 mM ) or high (20 mM ) NO 3 - -N concentrations were supplied through a subsoil irrigation system installed in a Hubbard loamy sand soil (sandy, mixed Udorthentic Haploboroll) at Becker, MN. Nitrate uptake and N 2 fixation were evaluated during two regrowth periods using 15 N. We also added small concentrations of Br - to the subsoil NO 3 - during three regrowth periods. Subsoil NO 3 - -N removal was similar for the seven N 2 -fixing entries, suggesting that selection for traits such as root system architecture, high forage quality, or multiple (>3) leaflets does not necessarily confer an advantage in NO 3 absorption. Even though 'Ineffective Agate' yielded less herbage than the N 2 -fixing entries, this non-N 2 -fixing cultivar removed about 38% more subsoil NO 3 - than N 2 -fixing entries over the growing season. These results confirm our earlier findings that non-N 2 -fixing alfalfa cultivars are likely to be more effective in phytoremediation of NO 3 - -contaminated sites than are standard cultivars. It also confirms our earlier conclusion that the simple difference technique may underestimate rates of symbiotic N 2 fixation when inorganic N supply is large. A strong correlation between 15 N and Br - uptake in the herbage (mg excess Br - = 25.2 x mg excess 15 N, r 2 = 0.97) led us to conclude that Br - can be used as a tracer of NO 3 - absorption by alfalfa in the field. This provides a new, dual-tracer approach for such studies.
Databáze: OpenAIRE
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