Phosphorus dynamics and movement in soil with long term manure application

The objective of this study was to examine the phosphorus (P) dynarnics (changes in soil P eithef in quantity or forrn) and P movement under field and laboratory conditions as irnpacted by 33 years of beef cattle manure application at rates equivalent to one, two and three times the normal recornmendation rates by Alberta Agriculture (1982), irrigation, and soil depth.Analysis of 33 years of soil total P data indicated increasing soil P concentration with increasing rate of ffranure application in the soil up to a depth of 60 cm, wliile depths between 60 to 150 cm did not show any significant difference in P concentration as at 2006 in comparison to soil total P (TP) in 1973.Soil TP decreased significantly with increasing depth as observed on the rrìanure plot as in 2006, and irrigation did not significantly (P > 0.05) affect soil total P. Leachatesamplescollectedatdepthsof 30,60and 120cn fromthemanuredplotsusing suction cup lysimeters showed a range of concentrations of dissolved phosphorus which can have negative impact on surface and groundwater quality.Total P concentration in unlrltered soil leachate samples ranged between 0 to 7 mg L-1, with a mean concentration of 4 mg L-1.Molybate reactive P concentrations are generally less than I mg L-l resulting in greater concentration of molybdate unreactive P.There is also a high possibility of P forms associated with colloidalparticles contributing to the observed high concentration of molybate unreactive P apart frorn the recalcitrant organic forms of P. Concentration of sulphate ion (83.8 -6313.9rng SOa2-L-r) and phosphate ions (0 to 7 mg L-r) in the leachate suggest possible anionic exclusion of phosphate ion from soil sorption sites with greater tendencies for the formation of calciurn sulphate minerals in the soil and Ca-P-colloidal cornplexes in soil solution.Movement of these forms of P that is attached to Ca and colloidal particles is a possible mechanism responsible for P leaching observed in the groundwater.Generally, P concentration varies with depths and the greatest volume of soil solution was sampled at 120cm depth.Irrigation events in summer 2006 did not have any significant effect on solution P concentrations.Sequential extraction of soil P suggests thatthe largestportion of P is associated with the NaHCOs and HCI extractable fractions of soil P. The NaOH extractable P fraction remains relatively constant by the rate of manure application, suggesting the limited impact of Fe and Al as P-retaining cations in calcareous system.Total extractable P (surn of P in the 5 extracts) increased with increasing rate of manure application at depths of 0 to l5 cm and significant irnpact of increasing rate of manure at 15 to 30 cm depth was only observed at rate of 120 Mg ha-lyr-I.Manure application significarrtly increased labile P fractions (form of P directly affecting P concentrations in soil solution) at all depth.ill The maximum, minimum and range of P concentrations observed in column leachates from soil samples at 0 to 15 and 15 to 30 cm layer increased with increasing rate of manure application.The inorganic P accounted for about 70 Yo of the P in the leachates.The maximum P concentrations were generally observed in these soils within the first 5 pore volumes, which is the same for both organic and inorganic forms of P.This confirmed that both organic and inorganic P forms are mobile.Analysis of the impact of column leaching of the clay loam soil with 20 pore volumes of 0.01M CaClz indicate that the HCI fraction was a source of P while the NaHCO3 fraction was a sink for P during the column leaching process.This is confirmed by drastic reduction in HCI extractable P and an increase in NaHCO: extractable P.This clearly indicates that the HCI fraction which has been classified as non-labile fraction significantly contributed to the P movement in this study.The water, bicarbonate and HCI fractions are the major extractable P fractions responsible for the leachate P concentration, as positive and signifìcant correlation was observed between these extractable P fractions and leachate P concentration.The highest rate of P movement was also observed at depth of 0 to 15 cm.These studies confirmed that the rates of ffranure application over a long period of time should be of concern from environmental point of view as long term manure loading increased soil P content, and rate of release of P into soil solution at favorable hydrologic IV condition.Excessive loading of P will eventually leads to possible negative impact on soil and water quality.Manure application in calcareous soil increased P forms associated with Ca.In the event of favorable hydrologic condition, the water, bicarbonate and HCI fractions, which constitute the largest fraction of extractable P, are the main P fractions that contribute to dissolved P in the soil.who gave me an opportunity to work with them as a graduate student.I will also want to acknowledge Dr. Xiying Hao forthe opportunity to use of one of the most important long term manure plots in Canada and the financial support that I received for my masters program.

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