SPECIATION OF PHOSPHORUS IN MANURE- AND INORGANIC FERTILIZER-AMENDED SASKATCHEWAN SOILS
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Concern over excess phosphorus (P) input and loading in some soils of the Canadian prairie region has led to a need for a better understanding of the fate of added manure and fertilizer P. Information on the effects of manure application over long term (i.e., years) and short term (i.e., weeks, months) as related to management practices and manure form is still lacking. Knowledge of the P forms and species present in soil following application of manure and inorganic P fertilizers, and linking this to potential P availability and mobility is needed to make sound P management recommendations. The objective of this thesis project was to assess the speciation of soil P in different manures and inorganic fertilizer-amended Saskatchewan soils as affected by time, presence and absence of plants, landscape position, soil type, and management practices including rate and placement. Three studies were conducted (growth chamber and field-based experiments) to study P behavior in soils. These studies closely followed a time scale, beginning with speciation and fate followed over the very short-term (i.e., days to weeks) to a short-term period (i.e., months to a year) following amendment application, and finally the effects of repeated annual manure additions made over the long term (i.e., 11 years). Soils used in this study were loamy textured Brown and Black Chernozems. Solid cattle manure (SCM) and liquid hog manure (LHM) were applied at low and high rates in the very short-term and long-term studies. The low rate of SCM and LHM application was 7.6 T ha-1 yr-1 (dry weight) and 37,000 L ha-1 yr-1, respectively which was equivalent to approximately 100 kg total N ha-1 yr-1 application (agronomic N rate). The high rate was four times this amount. Inorganic fertilizer (mono-ammonium phosphate blended with urea) at rate of 54 kg N ha-1 and 12 kg P ha-1 and SCM at rate of 60 T ha-1 were applied in the short-term study. A sequential chemical extraction procedure was used to fractionate P in very short-term and short-term studies and different soil test phosphorus (STP) methods were used to determine effects on the labile P in the long-term study. Changes in P speciation with time and their relative proportions in fertilizered soils were also assessed using the synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy in all studies. This study has revealed that manure, especially SCM elevates labile P over all time frames examined. Over the very short-term (i.e., weeks to a month), P was added as manure tends to remain in labile forms like brushite and adsorbed P that is accessible to plants for uptake. In the manure band (months to a year), manure P was relatively unchanged over a period of months while in the mono-ammonium phosphate (MAP) fertilizer band, adsorbed and Ca-P was readily formed from fertilizer P. Aging over several years (one to eleven years), along with high soil pH and high Ca:P ratio enhanced formation of more stable Ca-P minerals like apatite, especially in SCM amended soil. Overall, the unique combined use of wet chemical analysis and synchrotron-based techniques in this thesis research has improved our understanding of fate and transformation of P added to prairie soils. It is suggested that future studies of fate of applied P in soil also utilize a combination of wet chemical and spectroscopic techniques, as this was shown to be a rewarding approach.
DegreeDoctor of Philosophy (Ph.D.)
SupervisorPeak, Derek; Schoenau, Jeff J.
CommitteeKnight, Diane; Walley, Fran; Siciliano, Steven; Niu, Catherine; Goh, Tee B.
Copyright DateApril 2013