REGULAR ARTICLE
Understanding the variability in soybean nitrogen
fixation across agroecosystems
M. E. Schipanski
&
L. E. Drinkwater
&
M. P. Russelle
Received: 21 April 2009 / Accepted: 2 September 2009 / Published online: 25 September 2009
#
Springer Science + Business Media B.V. 2009
Abstract Legume-based cropping systems have the
potential to internally regulate N cycling due to the
suppressive effect of soil N availability on biological
nitrogen fixation. We used a gradient of endogenous
soil N levels resulting from different management
legacies and soil textures to investigate the effects of
soil organic matter dynamics and N availability on
soybean (Glycine max)N
2
fixation. Soybean N
2
fixation was estimated on 13 grain farm fields in
central New York State by the
15
N natural abundance
method using a non-nodulating soybean reference. A
range of soil N fractions were measured to span the
continuum from labile to more recalcitrant N pools.
Soybean reliance on N
2
fixation ranged from 36% to
82% and total N
2
fixed in aboveground biomass
ranged from 40 to 224 kg N ha
−1
. Soil N pools were
consistently inversely correlated with % N from
fixation and the correlation was statistically signifi-
cant for inorganic N and occluded particulate organic
matter N. However, we also found that soil N uptake
by N
2
-fixing soybeans relative to the non-nodulating
isoline increased as soil N decreased, suggesting that
N
2
fixation increased soil N scavenging in low
fertility fields. We found weak evidence for internal
regulation of N
2
fixation, because the inhibitory
effects of soil N availability were secondary to the
environmental and site characteristics, such as soil
texture and corresponding soil characteristics that
vary with texture, which affected soybean biomass,
total N
2
fixation, and net N balance.
Keywords Legume nitrogen fixation
.
Soil organic matter
.
15
N natural abundance
.
Soybean
.
Nitrogen cycling
.
Agroecosystem
Introduction
Humans have more than doubled the global rate of
reactive nitrogen (N) input into terrestrial systems,
resulting in major direct and indirect effects on
ecosystems (Vitousek et al. 2002a;Gallowayetal.
2003). Haber-Bosch N (HBN) fertilizer is the primary
contributor to this increase and its application contrib-
utes to large environmental consequences, including
surface water eutrophication and the formation of the
annual hypoxic zone in the Gulf of Mexico (McIsaac et
al. 2001; Galloway and Cowling 2002). The advent of
Plant Soil (2010) 329:379–397
DOI 10.1007/s11104-009-0165-0
Responsible Editor: Euan K. James.
Electronic supplementary material The online version of this
article (doi:10.1007/s11104-009-0165-0) contains
supplementary material, which is available to authorized users.
M. E. Schipanski (*)
:
L. E. Drinkwater
Department of Horticulture, Cornell University,
134A Plant Science Building,
Ithaca, NY 14853, USA
e-mail: mec62@cornell.edu
M. P. Russelle
USDA-ARS-US Dairy Forage Research Center,
1991 Upper Buford Circle,
St. Paul, MN 55108, USA