See more from this Session: General Wetland Soils: I
Monday, November 1, 2010
Long Beach Convention Center, Exhibit Hall BC, Lower Level
Cultivated Histosols in the Everglades Agricultural Area (EAA) are being converted to wetlands as part of Everglades restoration projects. Elemental S is used in the EAA to decrease pH and to increase nutrient availability to crops. The microbial oxidation of elemental S to sulfate may alter the utilization patterns of electronic acceptors when soils become flooded. The objectives of this study were to determine short-term changes in P dynamics and greenhouse gas production under different hydrologic conditions: drained soil, flooded soil, flooded soil+SO4. The distribution of P in labile, Fe-Al bound, Ca bound, humic-fulvic acid, and residual pools under drained, flooded, and sulfate-reducing conditions were measured for fields under sugarcane cropping, vegetable cropping, and uncultivated soil. The land uses were differentiated by P storage in different pools as cultivation contributed to higher pH and increased P sequestration in Ca-bound fractions more for sugarcane (50%) and vegetable (49%) than uncultivated soils (17%). Uncultivated soils sequestered more P in organic pools, as storage in residual fractions (70%) was higher than for sugarcane (38%) and vegetable (43%) soils. But the distribution of P in all fractions did not differ in response to flooding. For all three land uses, mineralizable N ranged from 20-30 mg/(kg*d), while inorganic N consumption averaged 10-20 mg/(kg*d) under both flooding treatments since NO3 was used as an electronic acceptor. Microbial CO2 production rates under flooded conditions were 50%, 62, and 72% of the aerobic rate for sugarcane, vegetable, and uncultivated soils, respectively. Methane production was minimal in the short-term under flooded conditions due to predominance of denitrification resulting from prior soil oxidation and organic N mineralization, or N fertilization, which contributed to maintenance of high enough levels of NO3 over the 10 d period to support denitrification. Methane production was minimal in S-amended soils due to stimulation of SO4 reduction. Short-term responses to flooding showed that CO2 is the primary endproduct of organic matter decomposition, with pathways of decomposition and P dynamics similar among land uses.