Controlled Environment Agriculture

Modeling of Evapotranspiration

Modeling Evapotranspiration and Hydroponic Solution Chemistry

Jennifer Mathieu

The research was conducted by then graduate student Jennifer Mathieu, a recipient of NASA's GSRP fellowship.

Our research on evapotranspiration was conducted in a research scale continuous-production system for lettuce. The system had automatic measurement and control of pH and dissolved oxygen (DO). Root zone temperature, electric conductivity (EC), and nitrate concentration were also measured automatically. Water loss from evapotranspiration was measured using a scale. Nitrate concentration measurements were used to model the dynamics of pH change and quantify nitrate uptake. A modification of the NICOLET model for nitrate uptake was created for the prediction of lettuce growth and nitrate uptake was developed as a first step in the creation of a real-time fault detection system whereby the monitoring of nitrate concentration in hydroponic solution could provide information about the health of a crop. This could provide early notification that a less than optimal set of environmental or biological conditions was negatively affecting the growth of the plants.

This work was published in part in:

Mathieu J., R. Linker, L. Levine, L. D. Albright, A. J. Both, R. M. Spanswick, R. Wheeler, E. Wheeler, D. S. deVilliers, R. W. Langhans. (2006). Evaluation of the Nicolet model for simulation of short-term hydroponic lettuce growth and nitrate uptake.Biosys Eng 95, 323-337.

The entire body of work may be found in the following dissertation:

Mathieu J. 2004. Lettuce crop evapotranspiration, nitrate uptake, and growth mechanistic simulation modeling : for use in fault detection in nydroponic production systems. PhD Dissertation. Cornell University. Ithaca, NY. 246 pg.