Re: Does the temperature of water affect the growth (height) of plant?

Cold irrigation water is a practical problem for greenhouse growers in cold 
winter climates. They sometimes use a system to heat the cold irrigation water 
prior to use.

You may be able to obtain a height decrease with cold irrigation water. Then 
again you might not. It would still be a good experiment even if you find no 
effect on plant height. It is good that you will be measuring water 
temperature and volumes applied.

The reason you might not find an effect on plant height is because cold 
irrigation water may only depress the soil temperature for about 30 minutes or 
so after irrigation. The volume of water can be important. If only a small 
volume of water is applied, only the soil temperature in the upper part of the 
pot might be depressed. The type of plant might make a difference. Tropical or 
subtropical plants, such as corn, African violet and tomato, might be more 
susceptible to cold irrigation water than more cold tolerant crops such as 
lettuce. 

Under your materials, you would need some way to heat or cool the water. Under 
procedure item 5, it would be best to specify actual target temperatures such 
as 0, 20 and 30 degrees C. The 20 C treatment would be the room temperature 
control. The cold water could be ice water or refrigerated water. The 30 C 
water could be heated in a microwave oven. 

It would be desirable to once measure the soil temperature at 5 minute 
intervals after irrigation with hot or cold water to see the size of the 
temperature change and how long it lasts. That data could be nicely presented 
as a graph of temperature on the vertical axis versus time on the horizontal 
axis.

Use at least three pots for each temperature treatment to provide replication 
and allow averages to be computed (Hershey 1995).

Height is not the best measure of plant growth. The process of handling plants 
to measure height can reduce their height. At the end of your experiment, it 
would be desirable to also take photos of the three treatment plants side-by-
side for a visual record and measure the shoot fresh weight per pot.


A google.com search will provide some data on irrigation water temperature 
effects on plants. 

You might also want to examine pages 146-147 of Masterlerz (1977) at the 
nearby University of Maryland, College Park library.

References

Mastalerz, John W. 1977. The greenhouse environment: the effect of 
environmental factors on the growth and development of flower crops. NY: 
Wiley. UMCP McKeldin Library Folio SB415 .M31 

Hershey, D.R. 1995. Plant Biology Science Projects. NY: Wiley.