AgriGold

August 2010 Update

by Bob Berkevich, August 16, 2010

Favorable weather conditions in the Spring of 2010, followed by a warm summer with adequate moisture in many areas has many growers optimistic about corn yields in the Northern Corn Belt for 2010. Corn growth and development are ahead of average, and especially ahead of 2009. Some areas have been challenged with excess moisture, with low spots in corn fields suffering from saturated soils or flooding. Please see below for information on GDU's and corn growth, as well as a look ahead to the harvest of 2010.

 The rate of corn growth and development is largely based on accumulation of heat throughout the growing season. A standard way of quantifying the amount of heat accumulated is by using growing degree units (GDU's), which are also known as heat units. This is a fairly straight forward calculation when given the daily high and low temperature.

 1. Find the daily high, but don't use any number over 86°F, since corn does not respond to temperatures above 86°F.

2. Find the daily low, but don't use any number under 50°F, since corn does not respond to temperatures below 50°F.

3. Add the numbers from steps 1 and 2, and divide by 2.

4. Subtract 50 from the number in step 3 to get the GDU's for that day.

 Example: High of 88°F, low of 64°F. Step 1:  Use 86°F for the high since corn does not respond to temperature above 86°F. Step 2:  Use 64°F as the low. Step 3: 86+64=150. 150/2=75. Step 4: 75-50=25 GDU's for that day.

Figure 1. GDU accumulation at Rochester, MN beginning April 20th for 2009 and 2010. Green bars indicate the amount of GDU's required for a 100 day hybrid to reach the given stage. Timing of corn development varies among hybrids.

Areas of fields with saturated soil can lead to problems later. Luckily, corn at or past the V6 stage can survive very wet conditions, although it can be stunted. Nitrogen (N) can be lost from soils in wet conditions in a few different ways. Course textured soils lose N via leaching down through the root zone. Medium and fine textured soils lose N via denitrification. In this process, N is lost as a gas to the atmosphere, with denitrification occurring more rapidly as temperature increases. In some cases of wet soils, N might not be lost, but the corn plant's ability to uptake N and other nutrients is hindered by the saturated and low-oxygen conditions. These corn plants might show the yellow signs of N deficiency, but should green up as soils dry out. Finally, if soils have been on the wet side for much of the growing season, shallow root development may hinder uptake of N that is out of reach. Shallow root systems and wet soils coupled with a strong wind event can lead to root lodging.

After vegetative growth, the corn plant shifts gears and utilizes all resources available to complete the reproductive cycle of filling the grain and making kernels. Nutrients are needed to make the sugars that are eventually converted into starch in the grain. Foliar disease, lack of fertility, compaction, saturated soils, insect damage, and cloudy weather are some of the conditions that can lead to a reduced ability of a corn plant to make those sugars. When these factors occur, the corn plant takes nutrients from stalks and roots to fill the grain (to complete reproduction) in a process called stalk or root cannibalization. Cannibalization predisposes corn plants to stalk and root rots, and corn that has gone through a period of flooding or saturated soils is even more vulnerable to stalk and root rots. As we are making our harvest plans this fall, remember in areas that were saturated for 24-48 hours or more may be lower yielding and may have reduced standability than areas that stayed drier.

Figure 2. Standing water in a Corn Field the day after a 3"rain fell on a field that was already saturated.  Prolonged periods of saturated soils can lead to N loss and predisposes 

Figure 3. Poorly drained fields with high rainfall corn plants to stalk and root rots.   Amounts may suffer lower yields with higher risk of stalk and root rots.

Categories: Corn Harvest

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