'N-sight' technique: a visual and quantitative analysis of urea hydrolysis and ammonia loss from soil.
Understanding individual and interconnected processes of nitrogen transformations in soil would benefit from recent developments in non-invasive, quantitative measurement technologies coupled with visualization techniques. ‘N-sight’ is a new technique under development that relies on the use of analyte-specific sensors impregnated into thin gels. The gels are inserted between the soil and glass wall of a rhizotron box and form a equilibrium with the soil solution. Specific optics excite and detect the chemical sensors to quantitatively measure the soil analyte of interest. Multiple single point measurements are arranged into a two-dimensional matrix and converted with software into intuitive visual images. The N-sight technique is demonstrated by following changes in soil pH caused by urea hydrolyzing to ammonium-N. Depending on soil type, the N-sight technique shows that soil pH begins increasing in less than one hour following application of granular urea and reaches a peak pH of approximately 9.5 directly under the point of application. Dynamic changes in soil pH with time and at different distances from the urea granule is clearly demonstrated. Ammonia volatilized into the headspace of the rhizotron box correlates with the magnitude of soil pH changes. Comparative analysis between urea and urea treated with the urease inhibitor Agrotain (N-(n-butyl) thiophosphoric triamide) shows the inhibitor slows the rate and magnitude of soil pH changes and correlates with a strong reduction in ammonia volatilization. The N-sight technique could be developed to quantify and visualize urea, ammonium-N, oxygen and potentially other analytes relevant for understanding or influencing the soil nitrogen cycle.