After the nice stretch of weather, a lot of corn and beans have been planted. If you dig some of your corn seeds you will see a radicle emerging and maybe some seminal roots. The picture to the right shows the seminal roots protruding from the bottom of the seed. These are temporary roots that anchor the plant and start nutrient take up as the energy and nutrients from the seed are depleted. The hook around the bottom of the plant is called the Mesocotyl, the length of the Mesocotyl is about half your seeding depth. The little bump you may be able to see above the Mesocotyl is called the crown. Your permanent root system called the nodal root system will develop out of the crown later.
The long white shoot above the crown is called the Coleoptile. As you can see there are two little leaves that are pushing out of the Coleoptile. The varieties of corn we plant in the Midwest have Coleoptiles that are only able to push out of the ground 4-5 inches. That is one of the reasons we aim for 1.25-2 inch planting depths. If the seed gets deeper, it sometimes runs out of steam to get the coleoptile all the way out of the ground or it can start leafing out underground under certain conditions, such as planting in wet conditions and having an open seed slot, or spraying chemicals such as Dual, and Dicamba (Basically chemicals that are seed growth inhibitors.)
Now some of you may have corn that is emerged and right away it was looking great, nice, and green. If you have looked at your corn in the last couple of days it may make you frown a little. The cooler temperatures and the cloudy days have been slowing down plant growth and function. There are a couple of important temperatures to remember for corn and soybeans. The magic low number is 50 degrees; after the temperature dips under 50 degrees reaction rates in plants drastically decrease. The substrates, enzymes, and reactants are moving very slow, think of each as a puzzle piece bouncing around. They need to bounce into each other at just the right spots to make reactions happen.
When temperatures are low they move at a slower pace taking longer for the puzzle pieces fit together just right. I was trying to make a graphic for this, but alas, my tech savvy is not as great as I wish it to be. The other temperature to remember is 86 degrees Fahrenheit. When the temperature is over 86 degrees there are no enzymes for the substrate and the reactant to attach to, therefore, no reactions take place. For every 18 degree increase in temperature, the speed of these reactions doubles. Photosynthesis and respiration are also affected by temperatures. Because these processes are responsible for fixing carbon and with carbon comprising the majority of the plant, lower temperatures mean plants grow slower, and look sick and yellow. If you really want to challenge your scientific mind take a look at this You Tube link that walks you through photosynthesis; it is a really complicated process that will blow your mind.
Soybean emergence is also starting. Before our cold snap the ground was pretty warm- leading to quick emergence of beans. If you notice the soybean that is just emerging from the ground in the picture, you will see the head of the soybean is still in the ground and there looks to be a neck or a hook. This helps the soybean head make it through the soil without breaking off. If the ground gets hard or crusts after planting, these heads can break off during emergence causing the bean to die. Good plant spacing for beans is important because they all help each other break through the soil. If you get a chance to go to the field during emergence notice the teamwork soybeans utilize for successful emergence.
A fun fact about soybeans is that the seed actually forms the cotyledons, and the first shoot out of the seed forms the roots, prior to the actual seed pushing out of the ground! If you take a look at the picture to the right you notice that there are two sides to the cotyledons each serving as a side of the seed. Once emergence happens, the growing point is on the top of the soybean plant; if the plant gets a hard frost or happens to get a lot of hail, it will more than likely die. Soybeans, however, are more hardy than we are led to believe. I have seen soybean plants that have been pretty stripped by hail but they still yielded about 40 bushels to the acre.
Corn is different though, the growing point is under ground until V5. That means the plant tissue above ground can freeze or be hailed on and your plant will still live. However, you will have a yield ding. I believe that yield hit is higher than univeristy data suggests at a 2-3 bushel decrease in yield. Fortunately, your corn can still have a great yield if it is hurt before V5.