Nitrogen Cycling in Seasonal Wetlands in Subtropical Cattle Pastures

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 (N min ) (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 N min 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 N min 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 NO 3 − and NH 4 + 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.