Reduced nitrate leaching and enhanced denitrifier activity and efficiency in organically fertilized soils

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.denitrification ͉ nitrogen ͉ organic agriculture ͉ sustainable agriculture ͉ integrated farming

Water controls on nitrogen transformations and stocks in an arid ecosystem

“…The rate of inorganic N accumulation in the resin represents the rate of N leaching below 25 cm. Giving the porous nature of soils at the study site, we assumed that flow paths were basically vertical and that the intercepting area ranged from a minimum of 3.14 cm 2 , which is the resin capsule top area, to a maximum of 31.4 cm 2 as suggested by Kramer et al (2006). The average of minimum and maximum leaching rates results in a conservative estimate to compare with N mineralization and uptake rates, because it assumes an area up to 10 times greater than the resin surface area.…”

Environmental impacts of organic agriculture in temperate regions.

“…In orchard systems in Washington State, Kramer et al [114] found 4.4-5.6 times greater annual nitrate leaching in conventional compared with organic plots. In irrigated processing tomato and maize production systems in California's Sacramento Valley, Poudel et al [115] found similar crop yields across organic, low-input and conventional farming systems over 5 years, but a lower potential risk of N leaching in the low-input and organic systems.…”

“…With a few exceptions [114,137], there is a scarcity of studies in N. America which have examined the impact of rotations characteristic of organic management on temporal variability of N 2 O emissions and overall GHG budget. Differences in the synchrony of N supply and crop demand between inorganic N and organic N (legume, compost) fertilized regimes will affect N 2 O emissions.…”

Temperature and Relative Humidity Affect Weed Response to Vinegar and Clove Oil

“…The authors speculated that similar reductions in nitrate loss might be found in non-perennial cropping systems as well. (Kramer et al, 2006) A summary of research results from a 22-year experiment comparing conventional and organic cropping systems at the Rodale Institute in Pennsylvania was published in the journal BioScience in 2005. Authors concluded that a number of environmental benefits-reduced chemical inputs, less soil erosion, water and energy conservation, and improved soil organic matter (higher soil carbon) and biodiversity-were superior in the organic systems.…”