On the pee! A mechanistic exploration of nitrogen and carbon cycling dynamics in the urine patch.

The project combines laboratory and field experimentation with data exploration and modelling to improve the understanding of factors controlling N and C dynamics within urine patches.

Mapping the dynamics of N and C cycling processes
Cattle urine will be applied to soil (upland and lowland) in the laboratory, and simultaneous changes in soil NO3, NH4, DOC, pH and redox concentrations in different (central, middle, outer and 'diffusive') zones of the patch will be determined through time. pH and O2 sensitive optodes will be used to vizualise and quantify changes in the soil environment. Microbial gene expression of N and C enzymes will be determined on soil samples.

Linking urine composition with N and C cycling
Urine will be collected from livestock grazing lowland and upland pastures and its composition determined before applying to soil and assessing effects on rates of N and C cycling and losses. 15N labelled urine will be used in a DENIS soil incubation (North Wyke) to determine effects of urine composition on the N2O:N2. 14C labelled purine derivatives, e.g. hippuric acid, will be applied at increasing rates to soil to determine their fate and effect on N cycling.

N and C cycling in urine patches deposited in different parts of a hillslope
Urine will be applied to different zones (hydrological) of a hillslope to test the hypothesis that differences in the soil's chemical, physical and biological properties, and climatic factors (e.g. wind speed - Redeker et al., 2015) affect N and C cycling and losses from urine patches.

Data exploration and modelling
The student will explore if new data from this project can be used to improve existing mechanistic N and C cycling models, e.g. DNDC, or if a statistical modelling approach can better reflect the changes in N and C cycling within different zones of the urine patch through time.

Redeker et al. (2015) Biogeosciences 12, 7423-7434.