Corn Emergence and Reasons for Uneven Stands  05/18/18 2:52:21 PM

 
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2018 Summer Field Tour Details
 
The 2018 tours will start with a “Stand Establishment Tour” on Wednesday May 30th  at our plot on the West side of Mynard Nebraska—1 mile South of our plant—1/4 west on Mynard Road OR 1-1/4 mile West of HWY 75 on Mynard Road—South Side of the Road.   The tours would last no longer than 1.5 hours and address any current agronomic issues as well as allow the attendees to monitor developmental progress of Asgrow and Dekalb genetics throughout the growing season.
 
Our Tentative Summer Tour Schedule
 
Date                                        Time                            Location
Wednesday May 30th              9:00 a.m.                     Mynard
 
This tour we will coin the “Stand Establishment Tour.”  A review of the spring planting process,  stand evaluations, weed control, etc., view/discuss examples of new seed treatments for corn and soybeans and what they have to offer, first looks and the new genetic lineup for 2019, and a Post-Planting Planter Clinic with Agri-Vision Equipment.
 
Bring a Friend and we will see you on the 30th at 9:00 a.m. 
 
 
 
Tuesday June 12th                   9:00 a.m.                     Mynard
Tuesday June 26th                   9:00 a.m.                     Mynard
Tuesday July 10th                    9:00 a.m.                     Mynard
Tuesday July 24th                    9:00 a.m.                     Mynard
Tuesday August 7th                 9:00 a.m.                     Mynard
Tuesday August 21th               9:00 a.m.                     Mynard
 
Wednesday August 29th ,WBI  Fall Mtg.  –Stay tuned for details
 
 
Once corn has emerged it has now accumulated approximately 120 (GDD) but is likely pale in color.  This is not uncommon and most every spring we experience a period of time in which these conditions present themselves—the root system is just starting growth and photosynthesis is not at full capacity yet. Discolored or pale emerging corn is natural since the coleoptile (shoot) and radicle/lateral seminal roots begin growth directly from the seed.  Growth of the seminal roots will slow to a stop at about V3.  After the seminal and nodal roots have finally developed and that corn has emerged the nodal roots will continue to further develop with every additional node of plant (on average 7-10 nodes total).  The nodal root system is the major supplier of water and nutrients to the plant by V6 (6 leaf corn).   This is important since the developing plant uses the kernel until about V6 for much of its nutritional requirements.  Once the nodal roots develop, then the plant roots into fertility zones for additional nutrient needs and the corn generally turns into a deeper green color.   The lack of nodal root development is part of the reason why the corn will have pale green/yellow color the past few weeks—along with cold weather, slow growth, wet conditions, insect feeding, etc.  The corn should now grow quickly and unfurl one leaf about every 3 days or every additional 65 GDD’s. 
 
Growing Degree Days for Corn Growth Stages for a 112 day Hybrid
Stage                                                     GDD (Growing Degree Days--base 50)    
Emergence                                                                         120
2 leaf-V2                                                                              200
V6—tassel initiation                                                        475
V10                                                                                        740
V14                                                                                        1000
VT (tassel emergence)                                                   1150
Silking                                                                                   1400
R4 (Kernel dough stage)                                                1925
R5 (Kernel dent stage)                                                   2450
R6 (physiological maturity—black layer)                 2700
*courtesy of Hollinger (University of Nebraska)
 
Seedling Corn Nutrients and Deficiency symptoms/considerations for each during seedling development.
 
Nitrogen (N).  Different hybrids can have different shades of green but vigorous growth. Nitrogen deficient plants will be stunted and pale green to yellow in color.  Nitrogen stress symptoms can be a factor of many things, including true soil nitrogen deficiency, moisture stress, poor root development, open seed trenches sidewall compaction which limits seminal root development, etc..
Phosphorus (P). Certain hybrids can be purple at emergence because of their genetic make-up.  Slow growing plants can be purple from moisture stress, poor root development, open seed trenches sidewall compaction which limits seminal root development—(similar with N deficiency) Plants that are phosphorous deficient typically have a purple or dark green color because leaf expansion is retarded more than chlorophyll and chloroplast formation. Plants grow slowly, stalks are thin and shortened, and maturity is usually delayed. Phosphorous deficiency is often confused with herbicide injury, especially when plants are small. Soil testing can reveal if phosphorous is deficient. 
Potassium (K). Potassium deficiency is characterized by yellow and brown margins beginning at the leaf tips and can often be confused with nitrogen problems. Like nitrogen, potassium is mobile in the plant so lower leaves are affected first. Soil testing can readily reveal problem soils.
Iron (Fe). Plants show interveinal chlorosis on the youngest leaves.  As the deficiency intensifies, the uppermost leaves may become almost white between the veins as chlorosis spreads to older leaves.  This problem is primarily limited to calcareous soils (high in lime)
Magnesium (Mg). Expressed as interveinal chlorosis on the older leaves and progresses upwards as the deficiency intensifies. Older leaves may become reddish-purple and the tips and margins may die. Not a common problem, but acid, sandy soils can show symptoms.
Sulfur (S). Sulfur deficiency appears as a general yellowing of young leaves. Do not confuse sulfur deficiency with nitrogen problems. Because sulfur is not as easily translocated within the plant, younger leaves show the visual symptoms first.           
Zinc (Zn). Corn exhibits interveinal chlorosis on the upper leaves. The veins, midrib, and leaf margin remain green. As the deficiency intensifies, bands develop on either side of the midrib and the leaves may turn almost white (“white bud” effect). 
 
Un-even emerging corn occurs every year..  As with many problems there is probably no single easy answer to this one. There are several factors that could cause uneven growth. This year, extended cold weather after planting has played a role with emerged stands in some of the early planted acres.  Compaction, Open Seed Trenches. Etc., can all play a role here.  We often consider uneven corn that is also discolored to be deficient in nutrients.  Although possible, remember that nutritional uptake at this stage of growth is a snails pace.  BUT, you can see some things walking these fields during stand evaluation.   
Example:
Why is corn be taller and greener in parts of the field usually associated with some compaction wheel tracks? That area is compacted and root limited—Right?  Corn height should be smaller in this area.
 
A reasonable, but not proven, explanation combines our knowledge of root growth and nutrient uptake.  .Nutrient deficiencies, do not explain all stunted corn situations  Plant nutrients are known to move to plant roots by the three processes of: 1) mass flow, 2) diffusion, and 3) root interception. Nitrogen as nitrate – N (NO3-N) moves to roots by mass flow as water is absorbed from the soil by plant roots. Phosphorus as (H2PO4- or HPO4=) and K+ reach the root by diffusion and root interception. In the diffusion process, the nutrient moves from an area of higher concentration (the soil particle) to an area of lower concentration (the root). Root interception is the process whereby the root comes in contact with the nutrient as it grows. Therefore, N can move over longer distance compared to P and K.
Loose soils, at planting result in having pore space (the open area between soil particles) with a high percentage of air and less water.  There was less air space under wheel tracks or where some other form of compaction existed. As roots grew into the pore spaces in these more compacted areas, there was more space occupied by water. Thus it was easier for young roots and young corn plants to get needed nutrients. As a result, plants in slightly compacted areas are showing up with better earlier growth.
 
GET READY---THIS WILL COME FAST
Corn Plant Development: V3 to V12 stages
 
(Vn (vegetative stages) based on visible leaf collars)
 
V3
  • 3 visible leaf collars
  • Occurs in the range of 300-375 GDU’s
  • All leaves and ear shoots that the plant will produce are being initiated (forming), plus the tassel.
  • Photosynthesis is now the energy source, replacing the seed as the food source
  • Growing point is below the soil surface, injury occurring to the leaves (i.e. hail, frost, insect feeding) will have minimal, if any, effect on final yield
  • Growth of the seminal root system is virtually complete as the nodal root system begins to function as the primary supplier of water and nutrients
  • Foliar feeding insects such as black or dingy cutworm should be monitored
 
 
V5-V6
  • Growing point is at, or near, the soil surface
  • Stalk elongation begins, and is entering a period of rapid growth
  • Yield components are being set in terms of the potential number of kernel rows
  • Tillers may begin forming
  • The leaves, shoots, and tassel have all been initiated and are located in the growing point
  • Injury to the leaves and/or stalk beginning to have greater impact on reducing yield potential, and if severe enough could result in plant death
  • Latest growth stage for some post-emergent herbicides to be applied, including for example, those with ALS mode of action.
  • Continue monitoring for cutworm injury
 
V8-V9
  • Period of rapid growth as new “V” stage is occurring about every 3 days
  • All leaves have been formed but most are still hidden in the whorl
  • Plant begins to lose lower leaves
  • Ear shoots visible behind leaf sheaths
  • Unrestricted root growth should measure about 18” deep x 15” wide, should have side-dress applications completed by now to avoid root pruning
  • Moisture and nutrient demands increasing rapidly
  • Fields not planted to insect-protected corn, such as YieldGard Corn Borer, should be scouted for 1st generation European corn borer.
 
V12
  • Determination of the number of kernels per row is in progress and will continue through about V17. (Remember, the number of kernels rows was established by V6)
  • Rapid stalk growth is occurring through internode elongation
  • New “V” stages occur every 2-3 days
  • Nodal root system expanding quickly
  • Cumulative nutrient uptake by this stage has reached 30%, 20%, and 30% of the total N, P, and K, respectively which the plant will ultimately use.
  • Water use may reach about 0.20” per day
  • Lack of nutrients, moisture stress, or crop injury due to weather events, insect or mechanical damage can seriously reduce the potential number of kernels
  • Monitoring for root feeding insects such as corn rootworm should be in progress.
 
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