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Phosphorus dynamics under different nutrient management regimes in the Sumas Prairie, British Columbia, Canada

University of British Columbia

Phosphorus (P) is essential to life. Depletion of phosphate rock may occur within 50-400 years, yet P application to soils continues and has resulted in over-application of manure and fertilizer contributing to contamination of water systems. The Sumas Prairie in British Columbia demonstrates the convergence of P deficiency and excess in alluvial soils with high organic matter (SOM) content and serpentinitic contributions. The objective of this study was to evaluate how nutrient management at four sites (i.e. dairy farm, turf farm, mixed manure and fertilizer, and uncultivated) influence P compounds, their solubility, and (de)sorption reactions occurring in surface soils and adjacent ditch sediments. Samples were collected at 0-20 cm, 20-50 cm, 50+ cm depths in soil at each site, and in ditch sediments. P was vertically mobile from the surface to 20-50 cm depth in soil, and accumulation in ditch sediments was evident. P concentrations declined in the following order: mixed > dairy ~ uncultivated > turf. P fractionation indicated the following relative composition of total P (Aqua regia): 55-80% stable (acid ammonium oxalate), 12-46% labile (HCl), 2-5% Bray, 2-7% Mehlich, and 10-50% organic P (NaOH-EDTA). Mineral P sources were attributed to apatite, P adsorped on amorphous aluminum oxide as a stable source of P, and calcium phosphate precipitate as a labile source of P. ³¹P NMR analysis of organic extracts indicated that Pi,(orthophosphate and pyrophosphate fractions) accounted for 69-100% of extracted P, and Po (predominantly phosphate monoesters) accounted for 0-31%. SOM was the most important factor determining P concentrations and sorption sites for the retention of P. Clay content and SOM were positively associated with increased degrees of P saturation. P content in soils and ditch sediments were below maximum adsorption. Processes of adsorption and desorption in these soils are influenced by competition of Po and Pi forms particularly in the dairy, mixed, and uncultivated sites where SOM content is high. There is potential for P loss and subsequent environmental contamination from topsoil and ditch sediments at the mixed site according to DPSox, and from topsoil and ditch sediments at all sites according to M3-PSR I and M3-PSR II.

Text

2015-05-25

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/53418

Soil Science

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/