The link between soil microbial biomass phosphorus and movement of phosphorus to watercourses

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Our approach is to investigate soil microbial P dynamics, the relationships between these processes and their individual risks of causing P loss from soil to water through microbial processes. The project is therefore designed to take a mechanistic approach to confirm the interaction of microbial P and hydrology on P movement to watercourses. We will investigate interactions in two contrasting systems, grassland, which has continuous plant cover and arable, where there are extended periods of sparse, or absent, plant cover. We will do this at a range of scales, firstly on a microscale in a series of microcosms representing the two systems and subjected to a range of hydrological stresses (ie. wetting & drying/rewetting or flooding). The small scale of these studies will enable us to utilise radio- (33-P) isotope tracers to link biomass P dynamics with P loss to watercourses. Secondly, on a larger scale, isolated soil monoliths (1 x 1 x 1m) of the two systems will be established and subjected to hydrological events simulating natural rainfall, including storms. Continuous on-line monitoring of microbial activity (by measuring carbon dioxide evolution from respiration) and determination of P in leachates will allow us to confirm the link between microbial activity and P transfer to water, and the importance of organic matter incorporation into the soils. Thirdly, the findings from the smaller scale studies will be verified at a larger, field scale using the unique facilities of IGER¿s Rowden Research Platform with its 1 ha lysimeters, and the long-term Broadbalk plants at Rothamsted. (Joint with BB/C505059/1).