Date of Award

5-2011

Level of Access

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology and Environmental Sciences

Advisor

Zhongqi He

Second Committee Member

M. Susan Erich

Third Committee Member

Thanh Dao

Abstract

Phosphorus (P) solubility following soil application of poultry manure (PM) is influenced by manure composition, soil physicochemical properties, and rhizosphere processes. As more than 42% of P in PM is insoluble, high application rates may result in accumulation of P that is not plant available. Objectives were to (1) use sequential fractionation to characterize inorganic (Pi) and organic (Po) phosphorus from PM, and determine the effects of laboratory drying, (2) examine short-term changes in soil P fractions following PM application, and (3) identify changes in soil P fractions and soil phosphatase activities induced by both rhizosphere processes and PM in soil planted with ryegrass. Sequential fractionation of PM revealed that most Pi was in the labile (H2O + NaHCO3) and relatively stable HCl fractions, representing 46 and 48%, respectively. HCl-Po represented 53% of total manure organic P. Drying induced transformation of NaHCO3-Pi to H2O-Pi, increasing P solubility 42-97% in the order of 65°C>22°C>freeze-dry>undried; therefore, freeze-drying is recommended as the method least likely to overestimate H2O-Pi. Incubation of soil with PM at 100 and 200 mg P kg-1 of soil revealed that H2O- and HCl-Pi from PM increased Pi in corresponding fractions from soil. However, whereas H2O-Pi from PM was rapidly transformed to other fractions, HCl-Pi remained elevated when soil received the high rate of PM (200 mg kg-1). This was not observed in soil that received PM at 100 mg kg-1, suggesting that moderate application may not increase relatively stable P in soil, or may increase this fraction more slowly than high application rates. In a greenhouse study, when ryegrass was grown with PM at 112 mg P kg-1 of soil, labile-Pi in the rhizosphere was 30% higher than unamended soil, increasing root P concentrations by 37% and total P uptake by 59%. While PM initially increased NaOH- and HCl-Pi, these fractions did not differ between treatments after 16 weeks. In conclusion, chemical and biotic processes may readily transform H2O-extractable Pi from PM into more stable forms, and transform slowly available Pi and Po into labile-P; therefore, a single PM application does not necessarily lead to accumulation of recalcitrant P.

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