LeFebvre Paul

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LeFebvre
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Paul
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  • Preprint
    Conversion to soy on the Amazonian agricultural frontier increases streamflow without affecting stormflow dynamics
    ( 2011-01) Hayhoe, Shelby J. ; Neill, Christopher ; Porder, Stephen ; McHorney, Richard ; LeFebvre, Paul ; Coe, Michael T. ; Elsenbeer, Helmut ; Krusche, Alex V.
    Large-scale soy agriculture in the southern Brazilian Amazon now rivals deforestation for pasture as the region’s predominant form of land use change. Such landscape level change can have substantial consequences for local and regional hydrology, which remain relatively unstudied. We examined how the conversion to soy agriculture influences water balances and stormflows using stream discharge (water yields) and the timing of discharge (stream hydrographs) in small (2.5 to 13.5 km2) forested and soy headwater watersheds in the Upper Xingu Watershed in the state of Mato Grosso, Brazil. We monitored water yield for one year in three forested and four soy watersheds. Mean daily water yields were approximately four times higher in soy than forested watersheds, and soy watersheds showed greater seasonal variability in discharge. The contribution of stormflows to annual streamflow in all streams was low (< 13% of annual streamflow), and the contribution of stormflow to streamflow did not differ between land uses. If the increases in water yield observed in this study are typical, landscape-scale conversion to soy substantially alters water-balance, potentially altering the regional hydrology over large areas of the southern Amazon.
  • Article
    Deep soils modify environmental consequences of increased nitrogen fertilizer use in intensifying Amazon agriculture
    (Nature Publishing Group, 2018-09-07) Jankowski, KathiJo ; Neill, Christopher ; Davidson, Eric A. ; Macedo, Marcia N. ; Costa, Ciniro ; Galford, Gillian L. ; Maracahipes Santos, Leonardo ; LeFebvre, Paul ; Nunes, Darlisson ; Cerri, Carlos E. P. ; McHorney, Richard ; O’Connell, Christine ; Coe, Michael T.
    Agricultural intensification offers potential to grow more food while reducing the conversion of native ecosystems to croplands. However, intensification also risks environmental degradation through emissions of the greenhouse gas nitrous oxide (N2O) and nitrate leaching to ground and surface waters. Intensively-managed croplands and nitrogen (N) fertilizer use are expanding rapidly in tropical regions. We quantified fertilizer responses of maize yield, N2O emissions, and N leaching in an Amazon soybean-maize double-cropping system on deep, highly-weathered soils in Mato Grosso, Brazil. Application of N fertilizer above 80 kg N ha−1 yr−1 increased maize yield and N2O emissions only slightly. Unlike experiences in temperate regions, leached nitrate accumulated in deep soils with increased fertilizer and conversion to cropping at N fertilization rates >80 kg N ha−1, which exceeded maize demand. This raises new questions about the capacity of tropical agricultural soils to store nitrogen, which may determine when and how much nitrogen impacts surface waters.