Biosolids phosphorus forms, transformation and bioavailability in soil

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Recycling of phosphous (P) is exteremly important as the phosphate industry predicts exhaustion of available P reserves in next 100 to 250 years. Land application of biosolids on agricultural lands helps closing the rural-urban nutrient cycle. However, to effectively manage biosoilds P in agro-ecosystems, a better understanding of biosolids P forms, transformation and bioavailability is required. Improper application rates can result in either losses of crop yield or P accumulation in soil with increased environmental risks. Total concentrations of P in biosolids generally fall in range of 1 to 5% dry weight basis, 70 to 90% of which is in inorganic forms. Understanding the bioavailability of biosolids P after addition to soil requires an understanding of not only the forms and amounts of P in these materials, but also the forms and amounts of elements or materials that can modify P behaviour, kinetics of P transformation and its interactions with soil and plant roots. Traditional speciation methods provide limited insight into identification of biosolids P compounds. As an alternative to chemical extraction, advanced spectroscopic techniques have been recently offered for characterization of P species in soil and amendments. The X-ray Absorption Near-Edge Structure technique is one of the latest spectroscopic tools for solid phase speciation of P. This technique can distinguish between precipitated and adsorbed phases of P. Different P compounds in biosolids have also been identified using P-31 Nuclear Magnetic Resonance spectroscopy, a technique that provides direct molecular and structural characterization of organic P. Through greenhouse and field study, biosolids P forms will be characterized using advanced analytical techniques. Effects of soil properties, moisture and temperature on biosolid P transformation over the study period will be evaluated. As well, biosolids P transformation in soil and rhizosphere, its bioavailability and mobility in the soil will be investigated. Finally, the residual effect of applied biosolid P in the soil will be quantified.