How to Measure the Rate of Transpiration in a Maize Plant

Transpiration occurs when plants evaporate water. According to the United States Geological Survey, about 10 percent of the moisture in the atmosphere is due to transpiration -- a surprising statistic when you consider that about 70 percent of the planet is covered in ocean. Whether you're trying to teach children about transpiration or determine your crop's watering cycles, measuring the transpiration of a maize plant requires a potometer -- an instrument that measures plant water uptake. As a plant takes in water, it evaporates the same amount of water.

Maize plant with stem
H-shaped potometer
Beaker
Water
Stopwatch

Instructions

- 1
  Fill the beaker with water in a sink.
- 2
  Set the bottom of the potometer in the water, and place the stem of the maize plant in the stem holder at the top of the device.
- 3
  Raise the bottom of the potometer out of the water. The capillary tube is filled with water.
- 4
  Tap the capillary tube lightly, until a small air bubble appears.
- 5
  Place the tip of the of the potometer back into the water.
- 6
  Start the stopwatch when the air bubble passes the origin mark on the capillary tube. The entire tube is is marked in fractions of inches.
- 7
  Stop the stopwatch at a predetermined time, such as 5 minutes, and record how far the air bubble traveled up the tube.
- 8
  Divide the distance the bubble traveled by the predetermined time limit, to calculate the rate of transpiration in the maize plant. For example, if the air bubble traveled 0.15 inches in 300 seconds, the transpiration rate would be 0.0005 inches per second.

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