Towards a Better Understanding of the Soil-Plant-Atmosphere-Water Continuum

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Our NSERC supported research is aimed at designing agricultural water management systems which conserve water and energy, while at the same time enhancing crop productivity. Studies are being undertaken to define crop water stress by developing models based on measurements of various plant canopy atmosphere parameters including vapour pressure deficit, canopy temperature, relative humidity, photosynthetic rate, and CO2 fluxes. However, preliminary work from our water management field studies has shown that NO2 fluxes are more environmentally significant than CO2. Nitrous oxide (N2O) is a significant greenhouse gas, influenced by the rate and timing of fertilizer application, irrigation and drainage practices, as well as by precipitation. High water tables contribute to soil anaerobic conditions, thereby promoting denitrification. We installed static Plexiglas chambers in the field, and manually collected gas samples in syringes, which we brought back to the lab for N2O analysis, using gas chromatography. This was a very time consuming and tedious method, and resulted in a backlog of samples in the lab, which took an inordinate amount of time to analyze. Furthermore, since we sampled manually, we often missed peak emissions, and were not able to accurately capture rainfall and fertilization effects. In addition, we often did not capture emissions due to increased microbiological activity under warmer soil temperatures during the spring thaw. There are two other complications with the collection of data manually. Firstly fluxes are not linear with time, so simple linear extrapolation between data points leads to erroneous estimates of N2O. Secondly, our data showed tremendous variability in N2O fluxes within sites. This leads us to believe that there are geospatially variable soil microbiological hotspots, influencing fluxes and we need to distinguish biological sources of N2O. We propose to use a PICARRO G5131-i N2O Concentration and Isotopes Analyzer, in order to overcome the above challenges, and to generate a better understanding of crop productivity under various soil-water conditions. It continuously and rapidly measures N2O gas concentration and isotopes (eg. δ15N). Through a Distribution Manifold we can simultaneously measure N2O concentrations and isotopomer ratios in up to 16 field-based chambers. The Small Sample Isotope Module 2 (SSIM2) of the Analyzer measures gas evolution from soils, vegetation, as well as the incorporation of stable labels into living organisms, which will completely modernize our method of evaluating N reactions in microbial-soil-plant environments. We will also be able to measure dissolved N2O evolution, an under-reported source of N2O. Approximately 25 graduate students will be trained in the use of the Analyzer. Through their training, they will become Canadian leaders in advanced environmental management for sustainable agriculture.