Title page for ETD etd-07112006-125540

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
  • phytoremediation phosphorus
Date of Defense 2006-07-06
Availability unrestricted
Phosphorus (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

double-cropped system.

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