Don't wait until the spring to plan for your next corn crop. The best time to start your planning for next year is the year before. That's why you need to stress-test your fields.
By: Darrell Smith, Farm Journal Conservation and Machinery Editor
Raising top corn yields, and turning a profit, is essentially a matter of dealing with crop stress—either avoiding it or minimizing its impact. That reality came into sharp focus during the record drought and heat of 2012. The only upside to that situation was that delving into the problems pre-harvest helped farmers grow bumper crops the following year.
If you walk your fields in any year, you probably will notice that all of your fields have not been equally stressed, says Farm Journal Field Agronomist Ken Ferrie. With harvest under way or just around the corner, it’s time to take stock of your fields.
Ferrie suggests a four-step process: First, locate your worst problem areas; second, determine the real cause of the stress (it might be more than drought); third, plan your harvest strategy; and fourth, fix the problems revealed during your inventory.
You need to scout your fields—but not randomly. "Zero in on stressed areas by studying yield maps and NDVI [Normalized Difference Vegetation Index] maps for the current crop and from previous drought years," Ferrie says. "They will show you where to look for problems."
While some fields may have stressed by lack of water, other problems might have worsened the effect. "You must identify those other stress points too," Ferrie says.
Stress multipliers. Likely stress multipliers include nutrient deficiencies, physical problems in the soil and pests.
"If corn experienced even a moderate nitrogen deficiency, the effects will show up severely under drought conditions," Ferrie says. The symptom is yellowing that starts at the tip of the leaf and runs down the center midrib.
In the less-stressed area of a field, count the green leaves below the ear and note how many have no nitrogen (N) deficiency symptoms. Compare this number to the equivalent number for plants in the more stressed area.
Other ways to identify N deficiency include sending plants to a lab for tissue testing and testing soil samples for nitrate content. "If you find a deficiency, plan to improve your nitrogen management in 2013," Ferrie says.
Also look for signs of potassium (K) deficiency. "Dry weather makes it hard for plants to take up potassium, especially if soil levels are low," Ferrie says. It may be too late to fix potassium problems this year, "but you want to make sure you never enter another drought season with soil levels below optimum."
With K deficiency, and also N deficiency, you should split the stalk from five nodes up downward through the crown and examine stalk quality.
"When a corn plant is unable to get nutrients from soil, it cannibalizes itself," Ferrie explains. "You see firing of leaves, and cottony pith moves down the stalk.
"With stressed corn, you worry about ears breaking loose in the shank and falling to the ground and about stalks collapsing from wind in the presence of stalk rot," Ferry says.
"Because of smaller ear size, you’ll want to move in the stripper plates on your combine head. The earlier you harvest, the better chance you have of pulling stalks through the stripper plates without breaking them and plugging the machine."
Harvesting early dramatically reduces harvest loss in tough crop conditions. Harvesting drought-damaged corn makes it more difficult to thresh the grain because cobs are rubbery and kernels are small. "Take time to calibrate yield loss, both at the header and in the threshing system, and adjust your combine settings as necessary," Ferrie advises.
Kernel damage and stress open the way for toxins in your grain. "Toxins really rev up as grain moisture falls," Ferrie says. "If toxins are present, they will build rapidly from 25% moisture on down. If you are planning to store damaged grain, dry it at high heat to less than 14% moisture, and screen out as many fines as possible."
Consider moving grain quickly, because grain from a drought harvest is harder to keep in condition. "If toxins, such as aflatoxin and vomitoxin, are not killed by the dryer, they can incubate on kernels while the grain is stored," Ferrie says. "Infection levels can climb. Grain that would be accepted by elevators in the fall may not be accepted in the spring. This loss is not covered by crop insurance."
Perhaps the only good thing that comes from a drought-damaged crop is information. "While harvesting drought-damaged corn is depressing and frustrating, these are the years that produce the most valuable yield maps for making future decisions about variable-rate application and stress management," Ferrie explains. "Do everything possible to get accurate calibration of your yield monitor."
Postharvest management. After harvest is finished, plan how to manage the expensive fertilizer your drought-stressed crop did not use. "With phosphorus, potassium and sulfur, you can just reduce the amount you’ll apply," Ferrie says.
"Nitrogen is tougher. High nitrate values in your soil mean nitrogen may be leached away by fall or spring rains. This may be the year to plant a cover crop, such as radishes or a grass, to try to suck up that nitrogen and hold it into 2013. But if you plant a cover crop, you must be prepared to manage it next spring."
Dry soil may also influence your liming program. "Soil tests that are taken during a drought tend to read more acidic," Ferrie says. "You don’t want to underlime, but you don’t want to overlime, either. Review the pH history of the field; if the pH reading suddenly dropped, the test may have been influenced by the dry conditions, and the soil may not be as acid as you think."
Few corn growers are sorry to bid farewell to 2012. Use the painful lessons from this season to set you on the path to profits next spring.
If aflatoxin is present in drought-stressed corn, and if it survives the drying process, it can pose a serious threat to human health, warns Farm Journal Field Agronomist Ken Ferrie. "If you find yourself with an infected bin that has been rejected by the elevator, take all the proper safety precautions to avoid inhaling the dust when you handle the grain," he says. Those safety measures include wearing a dust mask or respirator to minimize inhalation risks as well as appropriate clothing such as long sleeves, pants and gloves.
USDA’s Grain Inspection, Packers and Stockyards Administration recently approved a new tool to detect aflatoxin. The ROSA Fast Aflatoxin Quantitative Test Kit from Charm Sciences, Inc., works with more than 20 feed and grain crops and provides results in about three minutes. (ROSA stands for rapid one-step assay.) For more details, visit www.FarmJournal.com/aflatoxin_test.
"See how low in the stalk the cotton pith has moved," Ferrie advises. "At the early milk and late-blister stage, I like to see the bottom two nodes pith-free. At the black layer stage, you want the bottom node intact to protect the integrity of the stalk."
Tissue testing can identify low K levels in the plants. "But, in a drought, you may find low levels of K in plants even when soil K levels are optimum," Ferrie says. "That’s because potassium is one of the first nutrients to become fixed and unavailable when soil dries out and collapses."
Soil problems. You might find you have adequate levels of nutrients in the soil, but the root system was compromised by compaction layers or poor structure. "Rooting problems, caused by poor soil structure, compaction or pests, will be magnified in a dry year," Ferrie says.
|Dry soil makes it easier to remove compaction and tillage layers. Set tools to shatter soil uniformly across the width of the implement.
To find out what’s causing the stress, "dig below the ground," Ferrie says. "At this point in the season, plants have the maximum number of roots that they will get. Clean off the soil, and see whether plant roots have moved downward at a 30° angle, as they should, or whether they have turned sideways on a density layer.
"You can get by with a little soil compaction in a normal year, but you’ll be crucified during a drought because of the lack of root depth," Ferrie continues. "Because of spring tillage and planting conditions, it’s not uncommon to find some soil types with severe compaction, compromising the roots, while other soils that drain better have a more ideal rooting environment.
"If you find a dense layer created by tillage, document the depth to the layer and how deep it extends in the soil. Plan to remove it later."
Dry years can be a good time to eliminate compaction, Ferrie notes, because dry soil shatters better. Plan now to have the tools you’ll need on hand after harvest.
"You’ll need to run deep enough to get below the layer, and you must shatter soil uniformly across the width of your vertical tillage tool," Ferrie says. "That may require more horsepower, narrower shank spacing or even waiting for moisture."
Another reason one part of a field is more stressed than another could be that it was planted too heavily. "You may find you need to adjust the population to match various soil types within the field," Ferrie says.
Pest symptoms. If there are no distinctive N or K deficiencies and no compaction layers present, but plants are still showing severe drought stress, the roots might have suffered from pest damage. You will need to identify the cause.
"Rootworms are easy to identify by the damage they do, stopping the growing point or cutting tracks up and down the root," Ferrie says. "Document and record this, especially if you use a GMO event for rootworm control. It may indicate you are running into resistant rootworms.
"While you may not notice corn nematodes in a normal year, they can bring corn to its knees during a drought," Ferrie says. "They are the toughest pests to identify and diagnose. Some can be identified on the outside of roots, but others are less obvious, so you may need to have soil tested at a laboratory."
Harvest stressed corn early. In corn, when stress occurs before flowering, it delays maturity, Ferrie explains. Stress after flowering, however, speeds maturity in corn plants.
As plants cannibalize themselves, trying to finish developing without nutrients and moisture, kernels abort and depth of kernel is lost. Stalk integrity is jeopardized.