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I have found several factors which are dramatically influencing crop yields this year:

1. 
   Corn variety
2. 
   Planting date
3. 
   CEC of the soil
4. 
   P&K soil fertility values
5. 
   Planting depth
6. 
   Previous crop
7. 
   Amount of rainfall received (April thru present) and sub-soil moisture availability

Currently, many farmers are interested in determining their expected corn yield for the 2012 crop.  I would use the following modified Illinois formula to make a corn yield estimation.

                Yield = avg. ear size (girth x length) x no. of ears per .001 A x 0.0112

                 = 16 rows x 32 (kernel length) x 31 x .0112 = 177.8 Bu/A

The formula is ok for a normal growing season, but this year I would add an additional component to the basic formula to compensate for the lack of kernel depth.  This component would be based on current crop status:

            Crop Status                 Component

            Fair to Good                        0.8

            Poor                                      0.7

            Very Poor                             0.6

            Extremely Poor                   0.5     

                                                                                                      

After the corn has tasseled for approximately 7 to 10 days, significant yield indicators are quite obvious.  On the individual ear, the girth (rows) around the ear can be counted.  Next, the number of ovules pollinated down the length of the ear can be counted.  The pollinated ovules will be rectangular shaped, and will later develop a pinkish color.  Then, make a determination on the number of pollinated ovules which could develop into kernels.  Finally, count the number of productive ears per .001A.

My observations on this year’s corn crop:

 

1. 
   Wide yield variations in short distances
2. 
   Multiple stress are significantly reducing yield
3. 
   Early planted, high fertility corn looks good
4. 
   The amount of rain received around the 4^th of July is critical

                                             

Today, 28 June, I saw my first tassel on 107 day corn planted on 24 April 2012.  This prolonged dry spell might slow both tassel and silk emergence on corn.

By the 4^th of July, I would like to see all herbicide spraying completed on soybeans.  By early July most soybeans will have begun to flower (R1).  On 13 June, I noted my first flowers on my 25 April planted soybeans.

With the continuing droughty weather conditions, two insects demand attention in our fields.  First, are the two spotted spider mites which are greenish yellow with two black spots on their sides.  They have four pairs of legs.  Hot, dry weather will allow the spider mite population to grow rapidly.  However, cool temperatures and high humidity will allow naturally occurring fungus to generally control the spider mites.

The second insect is the Japanese beetle.  These beetles are iridescent copper and green with white hair tufts on their sides.  My concern is with their feeding on corn silks prior to pollination.  If the silks are exposed (showing) from the ear shoot, things are ok for pollination to occur.  Silks are generally fertilized 24 to 48 hours after they emerge if corn pollen is present.

                                                       

                  Spider Mites (photo by ISA)                                          Japanese Beetle (photo by Iowa State Univ. Ext.)

1. 
   Planting time

• 
  At this time we determine the maximum possible numbers of plants per acre.
• 
  We establish our “effective planting depth” for the kernel.  This can have a dramatic influence on the later nodal root development.

2. 
   V₅ – V₆

• 
  At this time period in the plant life, the ear girth is determined (number of rows around the ear).  A row of kernels around the ear can add 7 to 10 Bu/A.

3. 
   V₁₀ – V₁₁

• 
  The maximum number of ovules which can potentially develop into a kernel is determined.  By adding another row of kernel down the length of the ear, you will add another 2.3 Bu/A.

4. 
   V_T

• 
  How many of the ovules are actually pollinated will determine the maximum ear size (kernels).

5. 
   R₁ – R₃

• 
  Not all pollinated ovules will be developed into kernels (kernel set).

6. 
   R₃ – R₆

• 
  Development of kernel (building kernel weight).

                                                             

Rain or lack of rain is on many farmers’ minds.  With our current weather conditions in eastern Iowa, potassium deficiencies are beginning to show up.  The following situations are generally associated with the potassium deficiencies this year:

1. The later planted corn is having a significant problem.
2. We are finding that the corn’s nodal root system is generally small and very restricted in depth, limiting nutrient uptake.
3. Compaction may be limiting rooting depth and overall development.
4. Dry weather is reducing nutrient availability in the upper soil profile.

At the Agronology 10 Research Center at Walcott in our corn variety plots, the following observation can be drawn:

1. Based on 5 hybrids, corn on soybean ground has approximately 4500 more plants per acre vs. corn on corn ground.
2. Corn height is about 45 to 48 inches tall on the soybean ground and about a foot shorter on the corn on corn ground.  In both of these areas, the corn was planted the same days, 24 April 2012.

On 13 June, I saw my first flowers on soybeans.  These soybeans were planted on 25 April 2012 and have a maturity group rating of 2.5 to 3.0.

 

Starting the week of 21 April 2012, many people began planting their 2012 crop.  At emergence time some of the fields had problems with corn leafing out underground.  There are generally two suspects for this early season problem:

 

1. 
    Soil crusting –

• 
  after a period of heavy rains a crust forms which impedes the coleoptile emergence above ground.
• 
  rotary hoe can be used to break this crust early on

2. 
    Cold soil temperatures – 

• 
  temperatures below 50° F can influence corn at germination.  From our weather data collected at the Agronology 10 Research Center at Walcott, IA, some concerns for possible problems can be developed.

                        Date (April)                  Day                    Min. Temp (°F)

                             23                          Monday                          34

                             24                          Tuesday                        43

                             25                          Wednesday                  50

                             26                          Thursday                       47

                             27                          Friday                             40

                             28                          Saturday                        38

                                               

The weather has had a significant impact on our 2012 crop.  From 17 April thru the 16 May 2012, the following maximum and minimum temperatures were recorded at the Ag 10 Research Center in Walcott, Iowa.

            Minimum Temperatures                    Maximum Temperatures

                 (°F)__          Number                           (°F)__           Number

               32-39                  4                               50-59                    6

               40-49                 14                              60-69                    4

               50-59                 10                              70-79                    7

               60-69                  2                               80-89                  12

                                                                             90-99                   1

In May, only two sub 45°F minimum temperatures are found, but there are 13 days where the maximum temperature exceeded 80°F or better.

A major problem with this spring weather has been the amount of rainfall received coupled with the extremely fine soil textures seen this spring.  From 28 April thru 16 May 2012, 5.1 inches of rain has fallen on the plots.  The 2.0 inch rain on Sunday night and early Monday morning (6-7 May) is causing the majority of the problems.  The overnight rain saturated the surface soil destroying soil tilth and creating a crusted soil condition.  In addition, this rain event limited oxygen to many germinating kernels.  As a result, in some corn fields, which were planted to soybeans in 2011, a less than desired plant population occurred.  What are your options?

   a)  If stands are 20,000 plants or better – keep it

   b)  If stands are less than 20,000 plants/A

        1)  Rotary hoe

        2)  Tear up the stand and replant

        3)  Do nothing                                        

                                                                                              

                 

The corn at the Agronology 10 Research Center planted on 24 April 2012, began spiking through the soil on Friday, 4 May.  So far in May, the research plots have received 5.1 inches of rain.  In one of the wetter areas, the corn has not spiked through the soil yet.  This delayed emergence is most likely caused by a lack of oxygen (too much water).  We may have to replant this wet area.

The Agronology 10 Research plots for both corn and soybeans were planted on 24-25 April 2012.  The surface soils were very dry and extremely friable.  Soil temperatures in the mornings were 50° F and 55° F at 4 inch depth during this planting period.  The plots received a total of 1.9 inches of rainfall Saturday and Sunday (28-29 April).

Presently, I have two concerns.  My first concern is that the rains could cause the soils to become crusted.  If the soil crusting is severe, then rotary-hoe to break up the crust, so germination is not negatively affected.  A second concern is the growth stage of the giant ragweeds where “pre” has not been applied to the stale seed bed.  Either a tillage operation is needed or a burn down herbicide plus a residual needs to be applied prior to planting.