Sasha B. Kramer*†, John P. Reganold‡,
Jerry D. Glover§, Brendan J. M. Bohannan*, and
Harold A. Mooney*†
Abstract
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 in other cropping systems.
Keywords: fertilized
soils, denitrification, nitrogen ,organic agriculture
,sustainable agriculture , integrated farming,
Organig farming.
