Thursday, September 18, 2014

The Effect Of Air Temperature On Plant Growth

Today the high temperature is 70 degrees Fahrenheit with the night time low of 46.  Did we really have 20 growing degrees today using the Growing Degree Day formula of 86 minus 50 equals GDD units?  I have been wondering about this all summer because it's been record cool here and in many places.

Dr. Elwynn Taylor Tweeted one day it takes at least 75 degrees for a high to do much good for plant growth.  Right now only our double crop soybeans need water and heat because the earlier planted crops are maturing.

"Thermoperiod refers to daily temperature change. Plants produce maximum growth when exposed to a day temperature that is about 10 to 15°F higher than the night temperature. This allows the plant to photosynthesize (build up) and respire (break down) during an optimum daytime temperature, and to curtail the rate of respiration during a cooler night. High temperatures cause increased respiration, sometimes above the rate of photosynthesis. This means that the products of photosynthesis are being used more rapidly than they are being produced. For growth to occur, photosynthesis must be greater than respiration.

Low temperatures can result in poor growth. Photosynthesis is slowed down at low temperatures. Since photosynthesis is slowed, growth is slowed, and this results in lower yields. Not all plants grow best in the same temperature range. For example, snapdragons grow best when night time temperatures are 55°F, while the poinsettia grows best at 62°F. Florist cyclamen does well under very cool conditions, while many bedding plants grow best at a higher temperature.
Buds of many plants require exposure to a certain number of days below a critical temperature (chilling hours) before they will resume growth in the spring. Peaches are a prime example; most cultivars require 700 to 1,000 hours below 45°F and above 32°F before they break their rest period and begin growth. This time period varies for different plants. The flower buds of forsythia require a relatively short rest period and will grow at the first sign of warm weather. During dormancy, buds can withstand very low temperatures, but after the rest period is satisfied, buds become more susceptible to weather conditions, and can be damaged easily by cold temperatures or frost."
I guess the question is how much different is the requirement for corn and soybeans compared to these examples?
Ed Winkle


  1. For cotton plants we calculate DD60s. The daily high plus the low divided by 2 then subtract 60. As example, 80 high plus 64 low equals 144 divided by 2 equals 72 minus 60 equals 12 DD60s. For a rice crop the same formula is used except it is based on 50 instead of 60.

  2. Thanks Swamp Dog. I didn't know you had different formulas for those crops. It makes perfect sense as I know each crop is a little different. I wonder how they came up with the 86 minus 50 formula?