Submitted to: Journal of Environmental Quality
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/27/2006
Publication Date: 10/27/2006
Citation: Sigua, G.C., Kang, W., Coleman, S.W. 2006. Soil profile distribution of phosphorus and other nutrients following wetland conversion to beef cattle pasture. Journal of Environmental Quality. 35:2374- 2382. Interpretive Summary: With the staggering number of wetland loss and adopting the concept of restoration and creation of wetlands as the first line of defense to mitigate unavoidable wetland loss, there is a serious need to understand the historical condition and/or chemical/biological functions of the ecosystems following a conversion of wetlands to agricultural functions. The ecological impact of wetland conversion must be fully considered and there is a need for further research to evaluate and compare the cumulative impacts of wetland conversion as a part of the overall landscape with respect to changes in productivity and soil properties. We hypothesized that wetland conversion to improved beef cattle pasture may not increase levels of soil nutrients, especially P due to animal grazing. To verify our hypothesis we assessed the dynamics of P and other soil nutrients as a result of the conversion of natural wetland to improved beef cattle pasture in southwest Florida between 1940 and 2003. Conversion of wetland to beef cattle pastures had significant effects on soil P dynamics and soil organic carbon pool. The amount of TOC and SOM in the pasture were about 96% and 86%, respectively, and were lower than the concentrations in the reference wetland. It appeared that conversion of wetland was proceeding toward a soil condition/composition like that of mineral soils. These results are important in establishing useful baseline information on soil properties in pasture and adjoining reference wetland prior to restoring and converting pasture back to its original wetland conditions.
Technical Abstract: Largely influenced by the passage of the Swamp Land Act of 1849, many wetlands have been lost in the coastal plain region of southeastern United States primarily as a result of drainage for agricultural activities. This study examined changes in soil TOC, pH, Mehlich-extractable nutrients, and P dynamics following conversion of wetland to beef cattle pasture. To better understand the chemical response of soils during wetland conversion, soil core samples were collected from the converted beef cattle pastures and from the adjoining reference wetland at Plant City, FL in summer of 2002 and 2003. Data that were collected from the natural wetland sites were used as the reference data to detect potential changes in soil properties associated with the conversion of wetlands to beef cattle pastures from 1940 to 2003. The average concentration of TP in improved pasture (n = 88) soils (284 mg kg-1) was significantly (p ' 0.001) lower than its levels in natural wetland (n = 32) soils (688 mg kg-1) in 2003. Compared with the adjoining natural wetlands, the improved beef cattle pasture soils, 63 years after being drained exhibited: (1) a decrease in TOC (-172 g kg-1), TN (-10 g kg-1), K (-0.7 mg kg-1), and Al (-130 mg kg-1); (2) an increase in soil pH (+1.8), Ca (+88 mg kg-1), Mg (+7.5 mg kg-1), Mn (+0.3 mg kg-1) and Fe (+6.9 mg kg-1); and (3) no significant change in Na, Zn, and Cu. Wetland soils have higher concentrations (mg kg-1) of Al- bound P (435), CaMg-bound P (42), FeMn-bound P (43), and organic P (162) than their levels in pasture soils of 172, 11, 11, and 84 mg kg-1, respectively. The levels of WSP and KCl-bound P were comparable between wetland and pasture soil. Results suggest that conversion of wetland to beef cattle pasture was not environmentally detrimental because the levels of soil nutrients especially P and N in the improved pastures were both showing decreasing trends between 1940 and 2003.