A Bacterial Biosensor to Measure Early Season Nitrogen Bioavailability in Cereal Crops.

There is a need for improved tests for early-season plant-available soil nitrogen, to inform farmers whether or not to sidedress young corn plants with fertilizer.  However, current soil tests are unreliable, as they only report levels of nitrogen in the soil and not the actual nitrogen health of the plant.  In corn, nitrogen is assimilated into glutamine before and after transport throughout the plant.  Previously, a bacterial Escherichia coli strain, known as GlnLux was genetically engineered in our lab to emit light in the presence of exogenous glutamine.  Leaf punch extracts can be incubated with GlnLux to report relative concentrations of glutamine using photon detectors.

We hypothesized that GlnLux has potential as a biosensor for plant-available soil nitrogen in juvenile corn, in both the greenhouse and field.  In the greenhouse, we found high correlation between different levels of applied nitrogen and GlnLux light emission from leaf extracts, indicating that the test may potentially serve as a good indicator of plant nitrogen health in the field.  In the field, we found significant correlation between GlnLux output and pre-plant nitrogen application rate.  We also performed correlation analysis of GlnLux output from field grown plants and soil nitrogen, total plant nitrogen, harvest biomass, kernel rows, grain and stover nitrogen, and grain yield, as well as SPAD, Greenseeker®, and Greenindex® measurements.

Our results suggest that GlnLux shows promise in providing information regarding plant nitrogen health as compared to commercially available tests such as the pre-sidedress soil nitrate test (PSNT), SPAD, Greenseeker®, and Greenindex®.  We are now working to replicate our results and develop them into a model which might in the future be used by farmers for better management of nitrogen fertilization practices.