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Soil-profile distribution of inorganic N during 6 years of integrated crop-livestock management

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Excessive accumulation of soil nitrate-N can threaten water and air quality. How integrated crop-livestock systems might influence soil-profile nitrate-N accumulation has not been investigated. Therefore, we determined soil nitrate-N accumulation during 6 years of evaluation of diverse cropping systems on a Typic Kanhapludult in Georgia, USA. Of the total change in soil nitrate-N content that occurred during 6 years (increase of 14 kg N ha-1/yr-1), an average of 60% occurred in the primary rooting zone (0-90-cm depth) and 40% occurred in the zone below typical rooting (90-150-cm depth). Soil nitrate-N accumulation was greater in cropping systems with greater N fertilizer input, while it was surprisingly insensitive to differences in harvested N output. Soil nitrate-N accumulation was greater under conventional tillage than under no tillage at all soil depths (5.1 ± 4.2 kg N ha-1 yr-1 greater at a depth of 90-150 cm), suggesting soil disturbance was a key factor in mobilizing N and keeping it more disassociated from the organic-inorganic cycling system. Grazing of cover crops had variable effects on soil nitrate-N content: greater soil nitrate-N content in the rooting zone at the end of 1 year(63 vs. 47 kg N ha-1), greater soil nitrate-N content in the zone below typical rooting at the end of 3 and 4 years (91 vs. 70 kg N ha-1), and lower soil nitrate-N content in the rooting zone at the end of 6 years (89 vs. 120 kg N ha-1). These results confirm the beneficial effect of no-tillage management on moderating nitrate-N accumulation in the soil profile and indicate a variable, but mostly neutral effect of cover crop grazing on soil nitrate-N accumulation.
Alan J. Franzluebbers , John A. Stuedemann
Kanhapludults , agricultural soils , conventional tillage , cover crops , cropping systems , disturbed soils , fertilizer application , grazing , livestock , nitrate nitrogen , nitrogen fertilizers , no-tillage , pastures , rhizosphere , soil depth , soil fertility , soil nutrients , soil profiles , Georgia
Soil & tillage research 2013 v.134
Journal Articles, USDA Authors, Peer-Reviewed
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