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An energy based indicator of plant health

Principal Investigator

Clarence Swanton & Roydon Fraser

Research Institution

University of Guelph / University of Waterloo

External Funding Partners

This project was funded in part through Growing Forward 2 (GF2), a federal-provincial-territorial initiative. The Agricultural Adaptation Council assists in the delivery of GF2 in Ontario.

Project Start

April 2014

Project End

October 2017


  • Determine if surface canopy-air temperature differential will increase as early emerging weeds are controlled.
  • Determine if surface canopy-air temperature differential will increase as the amount of nitrogen applied to corn is increased to an optimum level.
  • Determine if, as crop plants mature, the surface canopy-air temperature differential will decline, i.e. become more similar to air temperature.
  • Develop a commercial prototype sensor based on the results of above objectives.


  • The development of new crop stress detection technology with direct application to precision agriculture, including precision applications of nitrogen or herbicides.
  • The enhancement of on-farm profitability while reducing the potential impact of agricultural practices on the environment.

Scientific Summary

Crop surface temperature is extremely important when it comes to crop health because of the amount of exergy received by the plant from the sun. “Exergy” is a term used in thermodynamics to label the maximum work that a system can perform on moving from a given state (i.e., crop is stressed) to a state of equilibrium (i.e., crop is healthy) within its environmental surroundings. Applying this thermodynamic theory, it is hypothesized that healthier plants should have a lower surface temperature during the day in order to gain access to more exergy from the sun. This research was focused on developing new technology that is capable of detecting physiological stress in crop plants caused by a nitrogen deficiency or by weed competition.

Using existing technologies, it is possible to detect differences in leaf surface temperatures based on high and low rates of applied nitrogen. A new method was investigated through this research project to detect physiological stress in crop plants using the the exergy destruction principle and thermal remote sensing of surface temperature to investigate its corresponding relationship to crop plant stress and yield. Evidence form this study has shown that exergy may be a novel approach to the development of new technology for precision agriculture. Mid-day and midnight relative surface temperature reversal was observed in the greenhouse (less stressed plants are cooler in the day and warmer at night relative to more stressed plants) consistent with the exergy destruction principle. Unfortunately, the time-related characteristics of surface temperature were beyond the scope of this current work due to a lack of suitable equipment for associated outdoor experiments. By adding time-related temperature information in future work it should be possible to increase the sensitivity of connecting plant stress with nitrogen needs and ultimately with plant yield. After conducting statistical analysis on the experimental data collected, it became clear that the variability will need to be better understood and accounted for in order to determine accurate surface temperature measurements. It has been determined that the variability in surface temperature between individual plants is on the order of the variability in the mean surface temperature between nitrogen stressed and less stressed plants. This means that without additional information, such as time-related information or averaging, it will be difficult to identify the optimum amount of nitrogen to add to an individual plant based on its surface temperature. Significant progress was made in proving the potential for this theory to be applied in precision agriculture and in identifying and potentially solving issues relating to the variability inherent in the experiments.

Project Related Publications