Driving through Kansas, it is difficult to miss fields of corn in the spring and summer. In an average year, more than 500 million bushels of corn are harvested in Kansas. That’s a lot! With numbers like that, one might believe it is easy to grow corn in Kansas. It goes well beyond just planting and watering though. There’s a science behind knowing when to plant corn, when to expect different stages of growth, and when to harvest – it’s called growing degree days (GDD).
In the spring, there are many important factors to consider when a farmer is thinking about planting corn. Are we done with freezes for the season? Is there moisture on the way? How much light is hitting my plants? While these are in the forefront of a farmer’s mind, another major factor is going to be temperature. We are not only talking air temperature, but also ground temperature.
According to the Kansas State University Department of Agronomy, if a farmer plants corn from when the ground temperature is between 50°F and 55°F, it can take 18 to 21 days to see emergence. If the farmer plants corn when the ground temperature is between 60°F and 65°F, it might only take 8 to 10 days to see emergence. What a difference! Iowa State University’s Department of Agronomy adds that corn will not grow below 50°F. Corn grows best in conditions between 50°F and 86°F. Between 86°F and 93°F, corn continues to grow, but the increase in temperature does not give additional benefit to the plant. Above 93°F, there can be a negative impact on the growth of corn. Above 110°F, true heat stress can occur on the plant. In general, warmer weather helps corn grow and cooler weather slows growth. It is recommended that students complete the Kansas Corn: Explore Corn lab prior to completing this lesson. This will help the students understand the growth stages of corn as they compete this lab.
Note: It is recommended that students complete the Kansas Corn: Explore Corn lab before completing the Kansas Corn: Growing Degree Days lab.
Growing Degree Days PowerPoint. Open it and show the students the slide with the United States (Slide 2). Have them identify all of the states from the map that are major corn producers. (Note: The numbers on the states are the percent of total corn production contributed to the U.S. supply.)
There must be a reason why corn is grown in these areas!
To gauge student knowledge, have students make a list of everything that can impact the growth of corn. Give them one minute. At the end of that minute, have them turn to a shoulder partner to compare lists. Encourage them to talk through the lists. From those lists, the partners will create a new list of the top five factors that can impact growth.
Bring the class back together and have students read off their lists. Write down their ideas on the board. If the same idea is mentioned, put a tick mark next to it. By the end, you will hopefully be able to narrow the list down to the top five impacts.
If students need help generating ideas, here are a few factors they may want to add to their list: location of the field, soil quality, pests in the field, the use of chemicals in the field, moisture, sunlight, soil temperature, and air temperature.
While all of those are important, farmers use a calculation called growing degree days (GDD). Now, hand out the Growing Degree Days Student Packet.
Have students read the first page of the Growing Degree Days Student Packet, which give students a background in growing degree days. Encourage them to highlight portions they think are important.
On the second page of the Growing Degree Days Student Packet, students are introduced to the Growing Degree Days (GDD) calculation.
This equation helps farmers calculate what stage of life their corn plant is in. It takes into account air temperature for any given day. The calculation is below:
The temperature will not always be between 50°F and 86°F. That is where a few rules come in when using the GDD equation. Make sure you explain these rules to students!
Remember, the growth process for corn halts with a temperature below 50°F; therefore, 50°F is our Lower Base Temperature. Also, remember that corn does not see a noticeable positive impact with temperatures above 86°F; therefore, 86°F is our Upper Limit Temperature.
So, if on a sunny May day, our high temperature was 70°F, and our low temperature was 54°F, our equation would look like this:
That would give us a GDD number of “12” for that sunny, May day. The more growing degree days we “accumulate,” the farther along the corn plant is in it growth. Often, students hear the term growing degree days, and think they are adding the number of days together. In actuality, you can accumulate many growing degree days in one day. It is simply a number.
After looking at the two examples in the Growing Degree Days Student Packet, show students the Growing Degree Days PowerPoint slide with information from the chart below (Slide 5). Have students work through the maximum and minimum temperatures to see if they can calculate the total number of growing degree days for that week. This concept is very unfamiliar to many students, so you may want to work through the data on Monday and Tuesday, then turn them loose to calculate the rest of the week.
Throughout this random week, our corn plant has “accumulated” 51.5 growing degree days.
According to the chart below from Clemson Cooperative Extension (this table is also in the Growing Degree Days Student Worksheet and in the Growing Degree Days PowerPoint), our corn plant would not have even emerged from the ground. We need to accumulate another 73.5 (125-51.5) growing degree days before that will happen. It could by the end of the next week!
With the rules explained earlier in mind, now have students practice by calculating the growing degree days for this random week in May. The chart below is in the Growing Degree Days Student Packet.
Now, students will get real world experience. Have them go to the High Plains Regional Climate Center Website.
The student instructions are in the Growing Degree Days PowerPoint (Slide 11), but when students go to the website, the map will be zoomed in on Kansas. Have them choose a field in Kansas (any field!) by clicking on the field and then “Create GDD Graph”. A chart will pop up for that field. The county where the field is located will be listed at the top of the chart.
Now, have students click back to the map they saw when they first went to the website. Have them back up the map on the website so they can see other highlighted states.
Possible answers for reflection questions:
1. Did any of the fields you chose never get to the R4 Date? If so, where? What do you think it means if the corn growth cannot make it to that level?
2. Based on your data, where would be the ideal place to grow corn? What are three reasons why?
3. What do you think would be the WORST place to grow corn in the United States? Why?
The goal of this activity is for students to gain a better understanding of how weather and climate have a major influence on crop growth. Farmers can use knowledge gained from previous years to predict when a crop will reach maturity. This helps with knowing when to harvest and when to spray pesticides. This is a great activity to revisit later in the growing season. Students can compare their data from earlier in the season to see how accurate it is with what actually happens.
To check for understanding, have students make their own “fake” growing degree days table. Have them make up a location, as well as come up with their own highs and lows. Emphasize that the table should be a mix of numbers between 50°F and 86°F, and some outside of that range. After creating the table, have them determine the number of GDDs for their week. Have them then exchange with another person in class to see if they get the same numbers.
Any educator electing to perform demonstrations is expected to follow NSTA Minimum Safety Practices and Regulations for Demonstrations, Experiments, and Workshops, which are available at http://static.nsta.org/pdfs/MinimumSafetyPracticesAndRegulations.pdf, as well as all school policies and rules and all state and federal laws, regulations, codes and professional standards. Educators are responsible for abiding appropriate legal standards and better professional practices under a duty of care to make laboratories and demonstrations in and out of the classroom as safe as possible. If in doubt, do not perform the demonstrations.
Investing in teachers is a priority therefore the Kansas Corn Commission is committed to providing materials and training to help teachers excel in the classroom. Teachers who seek to expand their knowledge and skill of connecting science with agriculture are encouraged to attend a Seed to STEM workshop.