Progress 10/01/03 to 09/30/08
Outputs
OUTPUTS: Soil mineralogical and chemical properties control phosphorus availability for plant growth while retaining most of this macronutrient in the solid phase, which inhibits losses to surface and ground water. To estimate phosphorus retention characteristics of organic and mineral soils, we completed screening analyses of soil phosphorus in samples of surface horizons from an organic soil (Belhaven) and a mineral soil (Cecil) in North Carolina. These results were submitted to the Multi-State project committee for consideration in selecting soil samples for the overall collaborative project. The committee ultimately devised plans for analyzing a number of soil samples for pedological characterization at the USDA-CSREES Soil Characterization laboratory in Lincoln, Nebraska, x-ray diffraction and thermal analyses in Florida and Kentucky, extractable iron, aluminum, and phosphorus analyses in North Carolina and Texas. Oxalate-extractable iron, aluminum, and phosphorus analyses were completed on two soil samples from Florida and two samples from Kentucky, and reported to the committee. Related research conducted at NC State University addressed the dissolution of phosphate from organic and mineral soils in a Carolina Bay on the Coastal Plain of North Carolina. When agricultural land is converted to a wetland, reduction of the soil will potentially increase the mobility of phosphorus. This phenomenon is a concern at a wetland restoration site (Juniper Bay) in southeastern North Carolina. Our research objective was to measure reductive P dissolution in soil samples ranging from organic to mineral soils collected from this drained, 250 ha Carolina Bay that had been farmed for up to 30 years before wetland conditions were restored. Results from this project were disseminated to both national and state (North Carolina) soil science professionals through poster presentations on phosphorus dissolution in soils from the wetland restoration project, and through publication of an M.S. thesis. PARTICIPANTS: Dr. Dean Hesterberg (Professor - Soil Chemistry) is the member of this Multi-State research project committee representing NC State University. Mr. Christopher Brownfield (M.S. student) completed his thesis research on relating phosphorus dissolution at a wetland site to the soil mineralogical and organic-matter properties. Ms. Kimberly Hutchison, a Research Technician in Dr. Hesterberg's laboratory completed analyses for this project. TARGET AUDIENCES: This project is aimed at developing a fundamental understanding of how soil matrix properties - particularly soil mineralogy and chemical properties - affects phosphorus retention. As such, the project results contribute to a mechanistic understanding of soil phosphorus management that is being addressed by applied scientists throughout the United States. In addition, wetland scientists are becoming aware of the possibility that phosphorus might be an environmental issue related to wetland restoration. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Both soils for our initial screening analysis had similar concentrations of Mehlich-3 extractable P (120 and 130 mg P/kg for Belhaven and Cecil soils). However, the Belhaven soil contained twice as much total P as the Cecil soil (900 versus 431 mg P/kg, respectively). In addition, both water-soluble and dilute calcium-chloride soluble P tended to be greater in the Belhaven soil. These results suggest that the organic soil had either a greater overall P retention affinity or a disproportionately greater amount of organic P. Also, the organic soil likely has more pH buffering capacity than the mineral soil, which could make the strong-acid Mehlich-3 extracting solution less effective for dissolving P from this soil. Wetland restoration is essential to counteract loss of wetlands to development. Agricultural land and forests are the two main sources of land for creating new wetlands. Research on Juniper Bay was a component of a larger project aimed at creating (restoring) a wetland at a 250-hectare Carolina Bay that had historically been agricultural land. While hydrologists focused on raising the groundwater level in the parcel of land without flooding, and other soil scientists focused on changes in soil properties towards those of a natural wetland, our goal was to ensure these soil changes would not cause a pollution problem due to excessive phosphorus release into surrounding streams. Often when soils are flooded, phosphorus is released to the soil water and mobilized. Simulations of soil chemical changes associated with wetting were carried out under laboratory conditions. Total soil P concentrations ranged from 8 to 19 mmol P/kg (250 to 600 mg P/kg) in the whole soils. The silt + clay soil fraction used in reduction studies contained 19 to 90 mmol P/kg (602 to 2800 mg/kg), with 57% to 78 % being organic P. During 25 d of reduction, there was no change in DRP in five of the six soil samples, while DRP doubled in the suspension of silt + clay from a deep, organic soil (Ponzer A). Although the Ponzer B sample did not release phosphorus, reductive Fe(II) dissolution during reduction was twice as great in this samples as in the Ponzer A sample. This disconnect between phosphorus and iron dissolution indicates that release of phosphate bound with Fe(III) was not the major mechanism operating in these organic soil samples. Because results indicated that only one of six types of soil in the Carolina Bay released significant amounts of phosphorus when wetland conditions were simulated, we tentatively concluded that phosphorus release will not be a concern during restoration of this wetland. Analyses of the project soils from Florida and Kentucky showed oxalate-extractable Fe, Al, and P ranging from 13 to 200 mmol Fe/kg, less than 13 to 120 mmol Al/kg, and 13 to 193 mmol P/kg. Extractable Fe was greater than Al in the soils from Kentucky, and Al was greater than Fe in the soils from Florida. Oxalate-extractable P was greater in the soils from Kentucky, consistent with the greater sum of extractable Fe + Al.
Publications
- Brownfield, C. S. 2007. Phosphorus dissolution in soil material from a Carolina bay as affected by reducing conditions. M.S. Thesis. Dept. of Soil Science, NC State University.
- Brownfield, C.S., Hesterberg, D. and Vepraskas, M. J. 2006. Phosphorus dissolution from a restored wetland. Abstracts of ASA-CSSA-SSSA 2006 International Annual Meeting. Indianapolis, IN, U.S.A. (184-1).
- Brownfield, C.S., Hesterberg, D. and Vepraskas, M. J. 2006. Phosphorus dissolution from a restored wetland. Proceedings of the 2007 Annual Meetings of the Soil Science Society of North Carolina, Raleigh, NC, U.S.A..
|
Progress 10/01/06 to 09/30/07
Outputs
OUTPUTS: Members of this multi-state research project met in November during the 2006 Annual International Meeting of the Soil Science Society of America in Indianapolis, IN. Plans were made for a 2007 summer meeting to discuss project results in detail. However, that meeting was cancelled due to conflicts in travel schedules for many of the participants. Related results from project work in North Carolina were disseminated to both national and state (North Carolina) soil science professionals through presentations on phosphorus dissolution in soils from a wetland restoration project.
PARTICIPANTS: Dr. Dean Hesterberg (Professor - Soil Chemistry) is the member of this Multi-State research project committee representing NC State University. Mr. Christopher Brownfield (M.S. student) completed his thesis research on phosphorus dissolution at a wetland site in relation to soil mineralogical and chemical properties.
TARGET AUDIENCES: This project is aimed at developing a fundamental understanding of how soil matrix properties - particularly soil mineralogy and chemical properties - affect phosphorus retention. Project results would provide a mechanistic understanding of soil phosphorus management in agriculture and the environment, and issue being addressed by applied nutrient-management scientists throughout the United States. Wetland scientists are also becoming more aware of the possible impacts of enhanced phosphorus mobility following wetland restoration.
Impacts
Soil samples from a Carolina bay were characterized and analyzed for their susceptibility to phosphorus dissolution and potential mobility under reducing (wetland) conditions. The Carolina bay was originally a wetland site that was drained and used for agriculture for approximately 30 years. The site is presently being restored to a wetland for the NC-Department of Transportation to receive wetland credits under the US National Wetland Reserve Program. The concern addressed by our research is that residual soil phosphorus from agricultural production will deteriorate water quality following wetland restoration because of phosphorus discharged to surrounding surface waters. Surface soil samples at the Carolina bay contained greater than 350 mg P/kg. Laboratory incubation results showed that dissolved phosphorus increased by up to 3-fold (up to 2.2 mg/L) in an organic soil at the site, but sandy mineral soils did not show the same trends. Nevertheless, these results raise
the issue that wetland restoration in agricultural soils should recognize the potential negative environmental impacts of increased phosphorus dissolution and mobilization under reducing soil conditions. We are presently seeking external research funds to develop a way to predict the susceptibility of any given soil to increased phosphorus dissolution, and to determine whether water-quality impacts from phosphorus is a widespread issue in wetland restoration.
Publications
- Brownfield, C.S., Hesterberg, D. and Vepraskas, M. J. 2006. Phosphorus dissolution from a restored wetland. Abstracts of ASA-CSSA-SSSA 2006 International Annual Meeting. Indianapolis, IN, U.S.A. (184-1).
- Brownfield, C.S., Hesterberg, D. and Vepraskas, M. J. 2006. Phosphorus dissolution from a restored wetland. Proceedings of the 2007 Annual Meetings of the Soil Science Society of North Carolina, Raleigh, NC, U.S.A..
|
Progress 10/01/05 to 09/30/06
Outputs
When agricultural land is converted to a wetland, reduction of the soil will potentially increase the mobility of phosphorus. This phenomenon is a concern at a wetland restoration site (Juniper Bay) in southeastern North Carolina. Our research objective was to measure reductive P dissolution in soil samples ranging from organic to mineral soils collected from this drained, 250 ha Carolina Bay that had been farmed for up to 30 years before wetland conditions were restored. Total soil P concentrations ranged from 8 to 19 mmol P/kg (250 to 600 mg P/kg) in the whole soils. The silt + clay soil fraction used in reduction studies contained 19 to 90 mmol P/kg (602 to 2800 mg/kg), with 57% to 78 % being organic P. Aqueous suspensions of the silt + clay fractions of field moist, surface-soil samples were subjected to microbial reduction in a continuously-stirred reactor while monitoring pH, redox potential (Eh), dissolved reactive P (DRP), dissolved total P, dissolved organic
carbon (DOC), dissolved Fe, Al, and Mn, and evolved carbon dioxide as a measure of microbial activity. Eh decreased from an average of 510 mV to -20 mV (pH 4.5-6.4) within 20 d of reduction. During 25 d of reduction, there was no change in DRP in five of the six soil samples, while DRP doubled in the suspension of silt + clay from a deep, organic soil (Ponzer A). Although the Ponzer B sample did not release phosphorus, reductive Fe(II) dissolution during reduction was twice as great in this samples as in the Ponzer A sample. This disconnect between phosphorus and iron dissolution indicates that release of phosphate bound with Fe(III) was not the major mechanism operating in these organic soil samples. These short-term incubation results suggest that dissolution and off-site movement of P from this restored wetland will not be a problem, except perhaps from the area of the deep, organic soil, a <100 ha area located in the center of the wetland.
Impacts
Wetland restoration is essential to counteract loss of wetlands to development. Agricultural land and forests are the two main sources of land for creating new wetlands. This research was a component of a larger project aimed at creating (restoring) a wetland at a 250-hectare Carolina Bay that had historically been agricultural land. While hydrologists focused on raising the groundwater level in the parcel of land without flooding, and other soil scientists focused on changes in soil properties towards those of a natural wetland, our goal was to ensure these soil changes would not cause a pollution problem due to excessive phosphorus release into surrounding streams. Often when soils are flooded, phosphorus is released to the soil water and mobilized. Simulations of soil chemical changes associated with wetting were carried out under laboratory conditions. Results indicated that only one of six types of soil in the Carolina Bay released significant amounts of
phosphorus when wetland conditions were simulated. Based on these results, we tentatively concluded that phosphorus release will not be a concern during restoration of this wetland.
Publications
- No publications reported this period
|
Progress 10/01/04 to 09/30/05
Outputs
The goal of this multi-state research project is to apply mineralogical and chemical analyses to determine precise chemical species of phosphorus occurring in a range of soils from throughout the United States. We previously reported that phosphorus in a sample of an organic soil (Belhaven muck) was twice as great as that in a mineral soil (Cecil fine sandy loam) from North Carolina, despite both soils having the same concentration of Mehlich-3 extractable phosphorus. Mehlich-3 extraction is a method based in soil testing analysis for fertility that is now used extensively to predict phosphorus movement and potential environmental impacts. Data from mineral and organic soils in North Carolina published elsewhere show that both organic soils and organic-rich mineral soils contained greater concentrations of oxalate-extractable aluminum through most of the soil profile than mineral soils containing less organic matter. Because oxalate-extractable aluminum (and iron) has
been correlated with phosphate binding capacity of soils, these data indicate that the organic-rich soils have a disproportionately greater P retention capacity than the organic-poor soils. Cancellation of the multi-state committee meeting originally planned for summer 2005 has postponed selection of a subset of screened soils for more in-depth analyses.
Impacts
One of the most important parameters affecting phosphorus mobility in soils is P retention by soil particles. Soils vary widely in their properties, making it difficult to uniformly manage excessive quantities of soil-applied phosphorus such that negative impacts on water-quality are minimized. This research will provide an understanding of differences in phosphorus retention mechanisms between soils that are rich in organic matter versus those dominated by minerals. Organic-rich soils are often found in the Atlantic Coastal plain and along major waterways. Because organic matter appears to have a major role in phosphorus retention processes, organic-rich soils may require unique management practices to minimize undesirable movement from agricultural fields to surface waters.
Publications
- No publications reported this period
|
Progress 10/01/03 to 09/30/04
Outputs
To estimate phosphorus retention characteristics of organic and mineral soils, we completed screening analyses of soil phosphorus in samples of surface horizons from an organic soil (Belhaven) and a mineral soil (Cecil) in North Carolina. Both soils had similar concentrations of Mehlich-3 extractable P (120 and 130 mg P/kg for Belhaven and Cecil soils). However, the Belhaven soil contained twice as much total P as the Cecil soil (900 versus 431 mg P/kg, respectively). In addition, both water-soluble and dilute calcium-chloride soluble P tended to be greater in the Belhaven soil. These results suggest that the organic soil had either a greater overall P retention affinity or a disproportionately greater amount of organic P. Also, the organic soil likely has more pH buffering capacity than the mineral soil, which could make the strong-acid Mehlich-3 extracting solution less effective for dissolving P from this soil. Our results were submitted to the multi-state project
group to use in selecting a subset of soils from across the US for more detailed analyses.
Impacts
Basic research is needed to determine the fate of phosphorus from fields receiving high rates of applied phosphorus. In North Carolina, a phosphorus indexing tool was developed to estimate relative amounts of phosphorus leaving agricultural fields. Results from this tool will be used to mandate restrictions on land-applied phosphorus for some producers, particularly those in animal production. Although the indexing tool developed in North Carolina is science based, we lack knowledge on phosphorus movement from organic soils. The NC-Department of Agriculture routinely analyzes soil phosphorus for producers using a method (Mehlich-3 extraction) suited to crop fertilizer needs. Because so many samples are analyzed annually, results from this procedure are used in the indexing tool to estimate whether or not a given soil contains excessive amounts of phosphorus. Our screening results suggest that this procedure may be deficient for accurately predicting environmental
impacts of phosphorus from organic soils.
Publications
- No publications reported this period
|
|