Dr. Dan Talks Agronomy
By Daniel Davidson
DTN Contributing Agronomist
Corn is rapidly moving through dent stage (R5). Excess rain early in the summer, shallow roots, shortages of nitrogen and a dry August have contributed to corn moving through grain fill more rapidly than expected. Any stress, including a shortened grain-fill period would reduce kernel weight by hindering dry matter accumulation.
Scouting now can help you decide when corn fields will be ready to harvest and how to prioritize fields in order to minimize harvest loss and maximize harvest efficiency. I like to note the variety, planting date and stress it might have endured as I do these last checks.
We're always looking for comparison years. Some have linked the 2015 season to 2008, a cropping year that started off early with good planting conditions and then, it rained and remained cool most of the summer. Much of the corn didn't mature before the first hard frost in 2008 and we were harvesting corn well into December. Much corn never did reach physiological maturity and it never dried down in the field on its own. Storing corn was a nightmare that winter.
We had plenty of planting delays in 2015 resulting in some late replanting, but it looks as though most of the crop will mature on time this year. Once corn begins to dent, it takes another 20 to 25 days to reach black layer or physiological maturity (R6). If dent occurred in mid to late August, corn should mature by the last week of September, well before the first hard frost hits.
Check stalk strength. Corn has been under some late-season stress as evidenced by premature senescence in many parts of the country. This is putting demands on the plant for carbohydrates to fill the ear as soon as possible. If the plant can't provide those demands through photosynthesis, it will begin to rob it from the stalk. This will weaken the stalk and allow stalk rots to move in prematurely and this increases the risk of fall lodging.
Fields differ in their susceptibility to lodging due to the hybrid planted, field conditions, the amount of stress encountered and if the plant was sprayed with a fungicide to maintain plant health. As we move into September, you can pinch the stalk above first node or push the stalk to see if it is weakening, which is a sign that lodging could happen. Harvest fields most at risk first. For more information on stalk rots go to: http://bit.ly/…
Check of stalk nitrates: Symptoms of nitrogen deficiency were evident in many fields in June and July due to heavy rains. Premature die back suggests corn did not have enough nitrogen to carry it to full term. A post-mortem stalk nitrate test can provide an assessment of whether the crop had the right amount of nitrogen, too much nitrogen or if nitrogen was limiting.
To test for nitrate in the stalk, cut 8-inch-long sections of stalk starting 6 inches above the soil surface from 10 representative plants. Cut these samples into 1-to-2-inch-long segments to facilitate drying and send to your local analytical laboratory. Stalks can be sampled between one quarter milkline to about three weeks after black layer.
Results will be in parts per million. If less than 700 ppm, nitrogen was limiting. If between 700 and 2,000, nitrogen was sufficient. If greater than 2,000, the available nitrogen was greater than needed. It's too late to help this year's crop, but it will give you some good information to make management decisions next year.
For more information on late season stalk nitrate testing go to: http://bit.ly/…
Dan Davidson can be reached at AskDrDan@dtn.com
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