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This article in SSSAJ

  1. Vol. 71 No. 3, p. 1058-1065
     
    Received: July 7, 2005
    Published: May, 2007


    * Corresponding author(s): pbohlen@archbold-station.org
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doi:10.2136/sssaj2005.00217

Nitrogen Cycling in Seasonal Wetlands in Subtropical Cattle Pastures

  1. Patrick J. Bohlen * and
  2. Stanley M. Gathumbi
  1. MacArthur Agro-ecology Research Center, Archbold Biological Station, Lake Placid, FL 33852

Abstract

Understanding the effects of agricultural land use on wetland N cycling is critical in areas such as south-central Florida, where widespread agricultural activities intersect with extensive wetland systems. We examined annual net N mineralization (Nmin) (buried-core method) and denitrification rates (acetylene-block method) in 24 small seasonal wetlands on a cattle ranch in this region, 12 each in intensively managed improved pastures (IP) and less intensively managed semi-native pastures (SNP). Wetlands in IP had less detritus, higher N concentrations, lower C/N ratios (0–15 cm), and higher microbial biomass N than did wetlands in SNP. Cumulative annual net Nmin was lower in IP wetlands (98 ± 17 kg N ha−1) than in SNP wetlands (133 ± 18 kg N ha−1). Nitrification was much lower in IP than in SNP wetlands and dominated net Nmin during the dry season (December–June), but was negligible during the flooded period (July–October). Cumulative annual denitrification was lower in IP wetlands (17.7 ± 3.4 kg N ha−1) than in SNP wetlands (34.7 ± 6.3 kg N ha−1). Soil N cycling rates correlated with NO3 and NH4 + concentrations, which correlated with soil C content. Our results show that the more intensive management of improved pastures was associated with declines in wetland soil C content and lower rates of nitrification and denitrification.

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