C.O.R.N. Newsletter: 2014-21

According to the National Agricultural Statistics Service (http://www.nass.usda.gov/Statistics_by_State/Ohio/Publications/Crop_Prog...) for the week ending 7-6-14, 4% of the state’s corn was silking which is in line with the 5-year average. Given the wide range in corn planting dates this year, some late planted (corn planted in early-mid June) will not achieve tasseling and silking until August. The pollination period, the flowering stage in corn, is the most critical period in the development of a corn plant from the standpoint of grain yield determination. Stress conditions (such as hail damage and drought) have the greatest impact on yield potential during the reproductive stage. The following are some key steps in the corn pollination process.

 Most corn hybrids tassel and silk about the same time although some variability exists among hybrids and environments. On a typical midsummer day, peak pollen shed occurs in the morning between 9:00 and 11:00 a.m. followed by a second round of pollen shed late in the afternoon. Pollen may be shed before the tassel fully emerges. Pollen shed begins in the middle of the central spike of the tassel and spreads out later over the whole tassel with the lower branches last to shed pollen. Pollen grains are borne in anthers, each of which contains a large number of pollen grains. The anthers open and the pollen grains pour out in early to mid morning after dew has dried off the tassels. Pollen is light and is often carried considerable distances by the wind. However, most of it settles within 20 to 50 feet.  

 Pollen shed is not a continuous process. It stops when the tassel is too wet or too dry and begins again when temperature conditions are favorable. Pollen stands little chance of being washed off the silks during a rainstorm as little to none is shed when the tassel is wet. Also, silks are covered with fine, sticky hairs, which serve to catch and anchor pollen grains.

 Under favorable conditions, pollen grain remains viable for only 18 to 24 hours. However, the pollen grain starts growth of the pollen tube down the silk channel within minutes of coming in contact with a silk.  The pollen tube grows the length of the silk and enters the female flower (ovule) in 12 to 28 hours. A well-developed ear shoot should have 750 to 1,000 ovules (potential kernels), each producing a silk. The silks from near the base of the ear emerge first and those from the tip appear last. Under good conditions, all silks will emerge and be ready for pollination within 3 to 5 days and this usually provides adequate time for all silks to be pollinated before pollen shed ceases.

 Pollen of a given plant rarely fertilizes all the silks of the same plant. Under field conditions 97% or more of the kernels produced by each plant may be pollinated by other plants in the field. The amount of pollen is rarely a cause of poor kernel set. Each tassel contains from 2 to 5 million pollen grains, which translates to 2,000 to 5,000 pollen grains produced for each silk of the ear shoot. Shortages of pollen are usually only a problem under conditions of extreme heat and drought. As noted above, poor kernel set is more often associated with poor timing of pollen shed with silk emergence – with silks emerging after pollen shed (poor “nick”). However, hybrids rarely exhibit this problem unless they experience extreme drought stress. Some of the new drought tolerant hybrids have shorter “anthesis silking intervals”, i.e. pollen shedding and silk emergence are more closely synchronized, than hybrids more susceptible to drought. This shorter anthesis silking interval may mitigate the impact of drought stress during pollination.

 For more on the pollination process in corn check out the following.

 Abendroth, L.J., R.W. Elmore, M.J. Boyer, and S.K. Marlay. 2011. Corn growth and development. Iowa State Univ. Ext. PMR 1009.

 Nielsen, R.L. 2010. Tassel Emergence and Pollen Shed. Corny News Network, Purdue Univ. [On-Line]. Available at http://www.agry.purdue.edu/ext/corn/news/timeless/Tassels.html (URL verified 7/7/14).

Nielsen, R.L. 2010. Silk Development and Emergence in Corn. Corny News Network, Purdue Univ. [On-Line]. Available at http://www.agry.purdue.edu/ext/corn/news/timeless/Silks.html (URL verified 7/7/14).

Persistent rains this year may force many growers to sidedress their nitrogen (N) in corn this year much later than what is considered normal. Other growers may be supplementing their earlier N applications to replace N lost from denitrification and leaching. The following are some suggestions from extension soil fertility specialists at Ohio State and Purdue University from past years that address various questions concerning N applications to corn after planting.

HOW LATE CAN N BE APPLIED? Corn utilizes large quantities of N during the grand growth stage. From the 8 leaf stage through tasseling N uptake is 4 to 8 pounds per day. For most corn hybrids N uptake is complete shortly after pollination. So, most of the N should be applied prior to the 10 leaf stage, with any supplemental applications complete by or shortly after tasseling.  Under conditions of severe N deficiency, some response would be expected to low rates of N (30 to 60 pounds) as late as three weeks after pollination.

WHAT IS THE BEST N SOURCE TO USE? Ammonia or N solutions knifed in are preferred in most situations, especially high residue fields. Granular urea can also be applied over the top in clean tilled situations, but those applications can be risky if rainfall does not come shortly after application.  Urea stabilizers (Agrotain) should be considered in high residue situations.  Granular urea broadcast in standing corn will cause some foliar burn when granules fall into the whorl. While it may appear unsightly, little yield decrease normally occurs if the fertilizer is applied prior to the 10-leaf stage.

HOW MUCH N SHOULD BE APPLIED? If the corn has gotten too tall to sidedress by this point (mid to late June), it has probably not been severely stressed and yield potential is still good. An example would be rotation corn after beans which had some starter or 28% applied with herbicides with good green color. Nitrogen rates should approach what was initially planned at the beginning of the season.  Research at Ohio State shows that decreased rates can do well, but do not decrease rates by more than 10-15%.  

CAN I BROADCAST 28-0-0 SOLUTIONS "OVER THE TOP"? Using broadcast applications of 28% N solution to sidedress N will cause some burn to foliar tissue of corn plants. 
 
The severity of injury is determined by the plant's stage of growth, the amount of N used and form of N. If the plant growing point is at or below the soil surface (or when plant has six collared leaves or less), the extent of foliar injury caused by burn will usually be negligible if the N rate is kept below 50 lb/acre. Even with higher N rates at later vegetative growth stages the injury from leaf burn is normally not so severe that it outweighs the potential benefits received from the N addition. The degree of plant burning is less with urea granules than with other N products.

Dribbling 28% solution with drop nozzles as a narrow band on the soil surface is an alternative approach that can help reduce foliar burning. Dribbling 28% is also a more efficient use of N than broadcast surface application because it helps reduce N volatilization.  Urea stabilizers may be considered for this application, but tillage is a major deciding factor on whether or not they are necessary.  High residue corn fields may benefit from urea stabilizers, but low residue fields are less likely to benefit.  At this point of the growing season, and the need for plenty of nitrogen by the crop, we do not recommend nitrification inhibitors.  We also rarely see positive responses to nitrification inhibitors when N is sidedressed.

CAN I APPLY N TO EVERY OTHER ROW? Research in Indiana, Illinois and Iowa has all shown that farmers can knife ammonia or N solutions in every other row middle (60 vs. 30 inch spacing) with no reduction in yield. The only caution is that extra attention must be paid, especially in wet conditions, that no knives plug with soil. A plugged knife in 60 inch spacing gives 4 rows with no N and will seriously reduce yields.

Another article on this topic published by Purdue University in 2011 can be found here: http://www.agry.purdue.edu/ext/corn/news/timeless/CornRespLateSeasonN.html.

Please register and plan to attend the OSU Extension and OARDC Western ARS Agronomy Field Day on July 16. Preregistration required for meal count by July 11, payable at the door $20. Register by email or phone to: Harold Watters (watters.35@osu.edu), 937 599-4227 or Joe Davlin (davlin.1@osu.edu), 937 462-8016.

Check-in is from 8:30 AM to 9

·         Wagon tour running from 9 to noon.

·         Lunch will include a meal and brief updates.

·         Choose one afternoon program from 1PM to 3PM with about an hour each with state Extension specialists.

CCA CEUs will be available. The Ohio Soybean Council provides support for our program. The new Field Guide for Corn, Soybean, Wheat and Alfalfa will be available for sale.

The location is the Western Agricultural Research Station, 7721 South Charleston Pike, South Charleston, Ohio 45368