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Large-Scale Assessment of Symbiotic Dinitrogen Fixation by Crops

Soybean and Alfalfa in the Mississippi River Basin

^a USDA-ARS, U.S. Dairy Forage Res. Cent. (Minnesota Cluster), St. Paul, MN 55108
^b Dep. of Soil, Water, and Clim., Univ. of Minnesota, 1991 Upper Buford Circle, Rm. 439, St. Paul, MN 55108

View larger version (51K): [in a new window]   Fig. 1. Spatial patterns of (A) total N harvested, (B) rate of symbiotic N2 fixation, and (C) fraction of total harvested N derived from symbiotic N2 fixation in alfalfa hay and haylage in the Mississippi River Basin in 1997. Rates are expressed per hectare of harvested alfalfa and plotted for hydrologic units.

View larger version (49K): [in a new window]   Fig. 2. Spatial patterns of (A) total N harvested, (B) rate of symbiotic N2 fixation, and (C) fraction of total bean N derived from symbiotic N2 fixation in soybean in the Mississippi River Basin in 1997. Rates are expressed per hectare of harvested soybean and plotted for hydrologic units.

View larger version (53K): [in a new window]   Fig. 3. Fraction of harvested crop area, yield, and production for soybean and alfalfa compared with data from 1997, which were used to estimate symbiotic N2 fixation. Data were obtained from USDA-NASS (2003b) for statewide totals (area and production) and means (yield). Note that the legend differs between crops because data from different states were included.