By Eric Anderson, Syngenta agronomist, CPAg
With summer over and fall in full swing, most growers have turned their attention toward harvest, which has started in earnest in some areas throughout the Great Lakes District. Looking back, spring planting was ideal (at least early on) and environmental conditions were mostly satisfactory, leading the USDA to predict near-record yields for much of the area. However, some growers who have begun harvest are finding a little different story, with lower than expected yields, especially for corn. Let’s look at the year and examine probable causes for potential corn yield loss in 2010 as well as possible solutions for future reference.
2010 Corn Crop
1.) Too much rain – One obvious cause for overall yield loss in 2010 was too much rain early on. Most areas had an over abundance of rainfall from mid-May through mid-July. Many growers experienced some flooding, at least in low-lying areas, and consequently had drowned out areas where corn was completely killed. Beyond those areas where the corn was killed, there were additional areas where the corn may not have been killed but was severely stunted or injured, greatly reducing overall yield. In most situations field conditions remained wet long enough that replanting these areas was not really a good option. In total, the drowned out and injured areas could have a significant negative impact on overall average yield for that field.
Possible future solution – Obviously we can’t control the weather or limit the amount of rainfall we get. However we can plan for potential replant situations and Syngenta Agronomy research has long term, multi-location research on corn replant management. This research focuses not only on how planting dates affect yield potential, grain harvest moisture content, and grain test weight in general, but also looks at how planting date affects individual hybrid performance and can help make specific hybrid recommendations for replant situations.
2.) Nitrogen Loss – The heavy rainfall from mid-May to mid-July hindered or delayed nitrogen application for many. However, a bigger problem was the amount of nitrogen lost from corn fields because of soils flooded or saturated for a prolonged period of time. Some nitrogen was likely lost through leaching but, depending on soil type, more was probably lost through denitrification, which is the conversion of nitrate form of nitrogen to nitrogen gas that escapes back into the atmosphere. Research has shown that average N loss from denitrification is usually around 2% of nitrate N per day of soil saturation, but it has been reported that under high temperatures nitrate nitrogen loss could be as high as 5% per day that soil is saturated. Based on this, some growers might have lost as much as one-third to one-half of their applied nitrogen. Obviously this could mean a big impact on final grain yield. Nitrogen shortage could also lead to potential lodging problems resulting in significant harvest losses.
Possible future solutions – There are several products available that can help stabilize or limit nitrogen loss from leaching, denitrification, and volatilization. Ask your nitrogen supplier about the benefits and uses of these products. Another remedy for in-season nitrogen loss is to apply more nitrogen if you think enough nitrogen has been lost to affect yield. There are tools such as chlorophyll meters or soil nitrate tests that can help determine if the crop is under nitrogen stress. Maybe just as dependable, though, is field assessment and visual observation. Side-dressing nitrogen, even if one has to dribble nitrogen on with a high clearance sprayer, can be a solution to replace nitrogen lost from flooding or prolonged periods of soil saturation.
3.) Leaf diseases and/or ear rots – Throughout much of the growing season we experienced above normal temperatures and rainfall, or at least high humidity. These conditions led to outbreaks of leaf diseases early on such as Common Rust, Northern Corn Leaf Blight, and Gray Leaf Spot, which may be the most detrimental of leaf diseases for yield loss. When these diseases are severe, the leaf area available for photosynthesis during the grain fill period can decline rapidly. This can result in “tip back” or kernel abortion and light test weight grain which reduces yield. Further, these diseases along with crown rots initiated during the seedling stage of development under saturated soil conditions, can lead to stalk rots resulting in yield loss due to harvest losses from down corn. Along with these problems, some areas there have reported ear rots, particularly Diplodia ear rot, at low to moderate levels. This is primarily the result of the wet and/or humid weather experienced during silking, and especially affects susceptible hybrids.
Possible future solutions – A possible solution for controlling leaf diseases is to apply an appropriate fungicide, which could be done either at V5 or R3 stage of growth and development, depending on the situation. Again, Syngenta Agronomy Research has recommendations based on research of fungicide application in general as well as specific hybrid response to fungicide application. Planting disease tolerant hybrids is another way to minimize foliar disease risks. With the extensive germplasm pool available in Syngenta’s breeding program, we offer the greatest amount of genetic diversity in the industry. This lessens the risk from disease problems by allowing us to create disease tolerant hybrids. Growers should scout fields prior to harvest for Diplodia or other ear rots to determine the severity of the disease. Fields with high levels of Diplodia or other ear rots should be harvested first, stored below 15% moisture and cooled below 50 degrees F to prevent further development of the fungus during storage. A final tool to help manage a potential disease problem is rotation away from corn in the field with a disease history and using tillage to help reduce crop residue that provides innoculum for disease outbreaks.
4.) Above normal temperatures and grain fill – Throughout much of the growing season we had above normal temperatures, both during the day and at night. At daytime temperatures above 86 degrees, corn plants have lower net photosynthetic energy production and therefore fewer carbohydrates assimilated and available for kernel development. Further, when night temperatures are above 70 degrees, corn plants expend more of the sugars gained during daytime photosynthesis on nighttime maintenance respiration. This is often referred to as “dark respiration” and can lead to lighter test weight grain, tip-back or kernel abortion, and lower yields. Because air temperature is the main driver of kernel dry weight accumulation for corn, high temperatures can shorten the grain fill period between flowering or pollination and physiological maturity or black layer formation and may actually reduce the number of days that a corn plant can “fill” grain. Again, this could result in kernel abortion or tip-back as well as lighter test weight grain and lower yield.
Possible future solutions – Because we can’t control the weather or how hot it gets during the growing season, our control of the problem of high temperatures reducing the grain fill period is limited. One possible solution to help alleviate the problem is planting a “hybrid package” of from three to five different hybrids, depending on number of acres. This enables growers to spread the maturity of the different hybrids to lessen the risk associated with above normal temperature during the grain fill period.