Soil Temperature and Cron Germination  04/02/18 4:06:03 PM

It’s COLD----But, Corn planting will soon begin in wide fashion.  Soil temperatures as of yesterday April 1st, remain in the mid to high 30’s.  The forecast calls for a cold and wetter week which will only make the soil temperature drop further.
 I would not recommend much if any widespread planting to occur just yet.  Germination, although slow, can begin at these current temperatures, however I would not expect it out of the ground very quickly. Corn hybrids today have better germination and emergence in cold/wet environments.  Under warm and moist conditions, corn emergence can occur in 4-5 days after planting, but under cool or dry conditions it may take up to 3 weeks to emerge dependent on the hybrids ability for germination under cold conditions—Hybrids do vary in this aspect!. Soil temperatures at this level will even slow water absorption into the kernel, which will limit active growth until we have some extended warm conditions to accumulate enough Growing Degree Day (GDD's) for the corn to emerge.
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)
Check the current soil temperatures as—under the soil temperature site tab!!
Days to 50% Corn Emergence from a 2-inch soil depth
Soil Temperature Days to 50% emergence
50°F 20 days
60°F 10 days
70°F 5 days
80°F 4 days

Optimal Planting dates are a debatable topic among producers and it seems the corn planting dates get earlier and earlier every year.  In the Eastern portion of Nebraska April 25th in the South and May 1st in the North would be considered to be in the ballpark for the day to plant your corn if you could plant it all on one day.  Time and equipment management, play a role in when you start and when you want to finish.  So it is an on-going debate of when to start and when you need to be finished.  Across Eastern Nebraska, corn planted April 20th-30th  on average will have the best yield potential.  Prior to April 20th the soil is usually cool (less than 50 degrees) and wet (field capacity) and can have continued establishment problems prior to emergence.  It generally takes about 125 growing degree units (GDU’S) for corn to emerge from the soil.  GDU’S are calculated from the soil temperature, not the air.  Uneven emergence is common in situations such as this.  It is very important to walk the early planted  fields and determine your population and if significant loss has occurred, be prepared to replant, but consider the initial planting rate, stand, calendar date, and yield potential of replanting.  Follow the example below.

Example:  Using the below table—(optimal planting date of April 30th):  If you planted 30,000 on April 30th and have a viable stand now of 15,000, the yield potential is 82%.   This table is useful for all replanting decisions (hail, soil crusting, insect damage, etc)
Planting                population (1000/ac)
  Date         10     15     20     25     30     35
Apr. 10        62      76    86     92     94     93
Apr. 20        67      81    91     97     99     97
Apr. 30        68      82    92     98    100    98
May   9        65      79    89     95     97     96
May 19        59      73    83     89     91     89
May 29        49      63    73     79     81     79
                         % of maximum yield
from Nafziger,E.D. 1994. Journal of Production Agriculture. &:59-62
Based of research in the Central Corn Belt by the University of Illinois.
Reducing Soil Compaction this Spring 
We talk about this every spring and given the current soil moisture content, probably worth a brief review. 
Factors Impacting Soil Compaction
The degree of soil compaction is determined by the moisture conditions of the soil at the time of application and by the weight of equipment. Soil water acts as a lubricant between soil aggregates, allowing these aggregates to become more tightly packed together. Soils compact more easily when soil moisture is at or near field capacity. Usually, this occurs the first day after a rain that a tractor could drive across the field. As a result, it is best to wait an extra day or two before planting or tilling a field that has been wet. When equipment loads are greater than 10 tons per axel, the compaction can cause too wet soils to extend to a depth of two feet or more.
Here is a real world example of soil compaction—Have you ever noticed when the Department of Roads is constructed a road bed prior to paving the road?  They usually have a really big and heavy disk attached to really big and heavy tractor.  As part of the construction process, they will disk that soil, which makes the road bed, for weeks prior to paving over it.  Sometimes you will also see a water truck watering down the soil, prior to the disking operation, trying to make the soil wetter so that it will compact better.  The objective is to make the road bed as hard as possible prior to paving.  Now this is an extreme example.  However, a fairly simple one demonstrating what tilling wet soil can do.
Effects of Soil Compaction
Several problems can arise from compacted soils:
  1.   Reduced root growth, causing stunted plants
  2.  Nutrient deficiencies due to decreased plant uptake.
  3. Decreased yield potential. Fields that have compacted soils can have a 10 to 20% decrease in yield.
  4. Need for more tillage to break up the compacted soil.
  5. Poor water infiltration
  6. Decrease in soil structure.
Additional research from Iowa State University stated that if heavy traffic continues on wet and compacted soils, yield losses over time in corn could be 4 to 6 bushels per acre and 2 to 3 bushels per acre in soybeans.  Now, many of the fore-mentioned effects of soil compaction are minimized if it rains all summer, but maximized if it turns dry.
Reducing Soil Compaction
There are several steps you can take to reduce your risk of soil compaction.
This is easy to say and hard not to do sometimes--do not work soils that are too wet. In addition to reducing the weight on each axel, adjust the tire size and air pressure to reduce the load on the soil surface. Research from Iowa State University showed that using equipment with 6 pounds per square inch (psi) of surface pressure, yielded 9 bushels per acre more than equipment with 16 psi. Before a field operation, test soil moisture using a hand ball or soil ribbon test and only proceed when proper soil moisture conditions exist.
Simple Test for Compaction-- A good soil should have a crumbly texture (like breadcrumbs). Compaction can easily be tested by pushing a pencil/pen/screwdriver/pocket knife into the soil with a normal, steady force. If the pencil/screwdriver/pocket knife goes in reasonably easily, the soil is not too compact—too wet..
The ribbon test is also a quick way to see how wet the soil really is and used to estimate soil texture and the amount of clay in a soil.  Place a small handful of soil in your palm. If it is dry add water drop wise until it is like modeling clay. Roll the clay into a cigar shape with about a 1/2-3/4 inch diameter. Place the cigar-shaped soil between your thumb and forefinger, and start to gently press the cigar into a flat ribbon shape. As the ribbon develops, let it extend over your forefinger until it breaks from its own weight. If the soil sample does not form any ribbon, the texture of your sample is sandy. If it does form a ribbon that is less than 1 inch and it feels: gritty, the soil texture is sandy loam; smooth, the soil texture is silty loam and; if neither gritty nor smooth, the soil texture is loam. If you are able to form a ribbon that is between 1-2 inches long and the soil feels: gritty, the soil texture is sandy clay loam; smooth, the soil texture is silty clay loam and if the ; soil does not have either a gritty or smooth feel to it, you have a clay loam. If you are able to form a ribbon that is more than 2 inches long and the soil feels: gritty, the soil texture is sandy clay; smooth, the soil texture is silty clay and if the ; soil does not have either a gritty or smooth feel to it the texture is clay.
Effects of fertility management on soybean yields
One of the historic questions soybean producers have often asked has been why soybean yields trend to plateau in the 60 bu/acre range, while corn yields have continued hit record levels.  2016 and 2017 were record years for soybean production in these parts.  Was this due to rain?  YES.  Was this due to fertility?  Maybe.  With all forms of crop production there is a recipe in what is needed in order to bring home a winner of a crop.  You can get record crops with marginal fertility maybe for a year or two.  At some point, the fertility part of the recipe will falter and then your crop is not a winner anymore. 
Research done by Dr. Barney Gordon, Professor of Agronomy at Kansas State University, indicates that soybean yield can be increased to higher levels with proper nutrient management.  Perhaps growers need to pay closer attention to which nutrients, if any, are applied to a soybean crop, and at what rates they are applied. This study looked primarily at various rates of P and/or K fertilizer. Two row spacings (7.5” and 30”) as well as two plant populations (150,000 and 225,000 p/a) were also used across the various fertility treatments.
Dr. Gordon’s research was conducted in the Belleville, KS area on a Crete silt loam soil, with a pH of 6.5, Bray 1 P of 23 ppm,  K soil test levels of 236 ppm, and an organic matter content of 2.8%. Crete soils are fairly common throughout much of South East and South-Central Nebraska.  The soil pH and fertility levels are certainly not extreme—if anything pretty good.  Below is a summary of fertilizer treatments that were applied in this study:
  1. 30 lb/a P2O5                                                   (low P – no K)
  2. 30 lb/a P2O5 + 60 lb/a K2O                          (low P  +  low K)
  3. 30 lb/a P2O5 + 120 lb/a K2O                         (low P  +  high K)
  4. 80 lb/a P2O5 + 60 lb/a K2O                           (high P  + low K)
  5. 80 lb/a P2O5 + 120 lb/a K2O                         (high P  + high K)
  6. 20 lb/a N  +  80 lb/a P2O5  + 120 lb/a K2O   (N-P-K)
  7. No fertilizer check
Soybean yields were essentially equal when comparing 7.5” and 30” rows  at 150,000 plants/acre, while the 30” row spacing resulted in a 4 bu/a advantage at  225,000 plants/acre, averaged across all fertilizer treatments.  The effect of fertilizer treatments, averaged across row spacing and plant population were:
Treatment                                Bushels/acre
                        No fertilizer check                              48
                        Low P                                                  57
                        Low P + High K                                 77
                        High P  +  Low K                               85
                        High P  +  High K                               85
                        N-P-K                                                 85
Dr. Gordon’s conclusions from this study were 1) in high yield environments, fertility requirements can be higher than normally recommended, and 2) fertility requirements can interact with other production factors.
John W. McNamara
Wiles Bros. Inc.
606 Wiles Road
Plattsmouth NE. 68048
(402) 298-8550--Office
(402) 499-3870--Cell
(402) 298-7174--Fax
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