Controlled Environment Agriculture

Lettuce Nitrate Modeling

Modeling of Nitrate and Root/Shoot Partitioning in Lettuce (NICOLET)

The purpose of the collaborative work is:

  • To gain carefully obtained data on the steady-state condition that could be used to develop specifications on minimal growth rates to limit nitrates in lettuce below the recommended thresholds.
  • To track the dynamics of nitrate change in a hydroponic lettuce food production system, as a means to 'flush' nitrates from the crop prior to harvest without reducing crop productivity.

The motivations for this study were to address the health hazards from high tissue nitrate in food crops consumed by humans, and the flow of excess nitrate into the environment. Development of a model of the influence of nitrate on carbohydrate partitioning will increase understanding of the processes and interactions at work. The current single-organ (whole plant) model (Seginer et al., 1998) was used as a starting point. This model was able to predict seasonal differences (summer to winter) of nitrate concentration. Refinement of the model may allow optimization of crop grow and reduction of nitrate in the harvested leaf tissue. Controlled Environment Agriculture (CEA) techniques provide the possibility for daily, continuous control of the environmental parameters, such as lighting, plant nutrient solution, CO2 availability, and temperature. These environmental parameters may be optimized for the refined model to provide possible methods of reducing nitrate levels in the crop.

One possible method of controlling nitrate concentration is to grow lettuce initially with abundant nitrogen supply, in order to maximize growth rate, and then interrupt nitrogen supply to reduce the nitrate concentration. The interruption will result in reduced growth and increase the root-shoot ratio, which will further reduce the growth of the shoot.

In addition to refinement of the whole plant model to root and shoot compartments, the model also will be modified in terms of water-nitrate relationships and nitrogen 'dilution' with age. The data we hope to obtain from the experiments will be used to calibrate a new version of the model and to estimate the plant response time to a nutrient solution nitrate concentration step function.

View the NICOLET model website

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Lettuce age 26 days grown with adequate nitrate supply has lower root to shoot ratio than plant shown below.

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Lettuce age 26 days grown with low levels of nitrate (starvation levels) shows larger root system than plants grown with adequate nitrogen supply.

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Hydroponic lettuce growing in a pond system: The lettuce is supported on pieces of foam and floats on a nutrient rich pond.