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[SANET-MG] reduced nitrate leaching on organic soils
Published online before print March 13, 2006
Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0600359103
Reduced nitrate leaching and enhanced denitrifier activity and
efficiency in organically fertilized soils
( denitrification | nitrogen | organic agriculture | sustainable
agriculture | integrated farming )
Sasha B. Kramer *, John P. Reganold , Jerry D. Glover , Brendan J. M.
Bohannan *, and Harold A. Mooney *
*Department of Biological Sciences, Stanford University, Stanford, CA
94305; Department of Crop and Soil Sciences, Washington State
University, Pullman, WA 99164; and The Land Institute, 2440 East Water
Well Road, Salina, KS 67401
Conventional agriculture has improved in crop yield but at large costs
to the environment, particularly off-site pollution from mineral N
fertilizers. In response to environmental concerns, organic agriculture
has become an increasingly popular option. One component of organic
agriculture that remains in question is whether it can reduce
agricultural N losses to groundwater and the atmosphere relative to
conventional agriculture. Here we report reduced N pollution from
organic and integrated farming systems compared with a conventional
farming system. We evaluated differences in denitrification potential
and a suite of other soil biological and chemical properties in soil
samples taken from organic, integrated, and conventional treatments in
an experimental apple orchard. Organically farmed soils exhibited higher
potential denitrification rates, greater denitrification efficiency,
higher organic matter, and greater microbial activity than
conventionally farmed soils. The observed differences in denitrifier
function were then assessed under field conditions after fertilization.
N2O emissions were not significantly different among treatments;
however, N2 emissions were highest in organic plots. Annual nitrate
leaching was 4.4-5.6 times higher in conventional plots than in organic
plots, with the integrated plots in between. This study demonstrates
that organic and integrated fertilization practices support more active
and efficient denitrifier communities, shift the balance of N2 emissions
and nitrate losses, and reduce environmentally damaging nitrate losses.
Although this study specifically examines a perennial orchard system,
the ecological and biogeochemical processes we evaluated are present in
all agroecosystems, and the reductions in nitrate loss in this study
could also be achievable
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