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Biological transformation of soil organic phosphorus in a long-term management trial

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Title: Biological transformation of soil organic phosphorus in a long-term management trial
Author: Fraser, Tandra
Department: School of Environmental Sciences
Program: Plant Agriculture
Advisor: Dunfield, KariLynch, Derek
Abstract: Biological transformations of phosphorus (P) in the soil are largely dependent on the functioning of the soil microbial community. The Glenlea Long-term Rotation Study site near Winnipeg, Canada was chosen to determine the effect of 20 years of no input organic (ORG), organic with composted manure (ORG+M), conventional (CONV) and restored prairie (PRA) management on alkaline phosphatase activity (ALP), bacterial phoD community composition, abundance and expression, and P availability. During a study at the site, soil chemical analysis revealed that NaHCO3-P was significantly lower in the ORG system, compared to CONV and PRA. Higher rates of ALP were reported in the ORG and ORG+M plots with a significant negative correlation to NaHCO3-P in 2011 (r2=0.71; P=0.03) and 2012 (r2=0.51; P=0.02). The significant correlation between phoD gene abundance and ALP activity suggests that it may be a better indicator of activity than phoD diversity. A greenhouse experiment using soil from the long-term management site examined the effect of form and rate of P amendment. For each soil, treatments of no P, composted cattle manure (low, medium and high), and mineral P as KH2PO4 (15, 40, 80 and 160 mg P kg-1 soil) were applied to pots containing 0.9 kg of each soil and planted to Italian ryegrass. Although ALP activity values at day 0 were similar among the ORG, CONV and PRA soils, by day 30 sampling the ALP was higher in response to P amendments in the ORG (5.38 to 6.23 μmol PNP g-1 hr-1) compared to the CONV (3.26 to 5.63 μmol PNP g-1 hr-1) and PRA (3.22 and 4.71 μmol PNP g-1hr-1) soils. As with the field trial, the higher ALP rates corresponded with higher phoD gene, but not transcript, abundance. Ryegrass plants harvested after 106 days showed a larger biomass response when amended with P compared to the control (no P) in the ORG and ORG+M than the CONV and PRA soils. These results suggest that management system may play a more significant role in influencing soil microbial and biochemical processes in soils than does the form and rate of P amendment.
URI: http://hdl.handle.net/10214/8807
Date: 2015-05
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