Type of Document Master's Thesis Author Ryan, Veronica A. URN etd-07112006-125540 Title Phytoremediation of a High Phosphorus Soil by Summer and Winter Hay Harvest Degree Master of Science (M.S.) Department Agronomy & Environmental Management Advisory Committee
Advisor Name Title Lewis Gaston Committee Chair Jim Wang Committee Member Maud Walsh Committee Member Keywords
- phytoremediation phosphorus
Date of Defense 2006-07-06 Availability unrestricted AbstractPhosphorus (P) loading into surface water from runoff and subsurface flow
leaving soils subjected to long-term applications of poultry litter (PL) will degrade water
quality. A practical way to reduce such loading is to remove soil P through plant uptake
and harvest removal. The primary field study presented here examined the
effectiveness of hay harvest utilizing a double-cropped system - perennial warm-season
forage grass, common bermudagrass (CB; Cynodon dactylon (L.) Pers.), overseeded
with annual ryegrass (ARG; Lolium multiflorum Lam.), a cool-season forage, in reducing
soil P from a Ruston fine-sandy loam impacted by PL amendments. A secondary field
study similarly examined CB, bahiagrass (BG; (Paspalum notatum Flugge.), crabgrass
(CG; Digitaria sanguinalis (L.) Scop.) and switchgrass (SG; Panicum virgatum L.).
The primary study was conducted as a randomized block design with three
replicate plots of four previous rates of PL (0, 5, 10 and 20 Mg ha-1) applied annually
(1996-2001) to CB sod, at the Calhoun Research Station in Calhoun, Louisiana.
Following the last PL application, plots were overseeded with ARG in Fall 2001, forage
harvested and analyzed for dry matter yield, tissue P concentration and P removal.
Double-cropped ARG and CB were harvested as hay and analyzed as above through
2005, giving four years of data. In Spring 2002, four small sub-plots BG, CB, CG and
SG were established in the upper end of the main plots used in the primary study and
corresponding data for these warm-season forages was collected for three years.
Over four years, ARG removed more soil P than did CB (112 vs. 76 kg P ha-1,
averaged across all rates of previous PL application and soil Bray2 P levels) because of
higher tissue P concentration. The double-cropped hay system, therefore, removed
nearly 200 kg P ha-1 or reduced soil P by about 100 mg kg-1. Despite low tissue P
concentration, high biomass production by SG extracted an average of 64 kg P ha-1
annually over three years. This rate was significantly greater than that for CB, BG or
CB, and perhaps equaled or exceeded the combined rate for ARG and CB in the
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