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From a short historical prospective, I am including the following data from our Agronology 10 Research Center at Walcott, Iowa. The norms are a 30 year average from the US Weather Service.

Table 1

Weather Data for 2010 thru 2013

Time Period (Months)                                        Rainfall (Inches)______________
      1 April – 31 July__          Norm          2010          2011          2012          2013

16.08          28.70        15.55         12.60         25.90

Observations

It is generally felt that a dry July will influence corn and soybean yields downward.

So how dry was the Ag 10 Research Center in 2013? The Research Center received only 2.55 inches of rain in July which is 63% of the norm.

Our June rainfall was slightly above average at 4.75 inches.

It is time to begin evaluating your corn fields now.

After the corn silks have turned brown, we can easily look at the ear girth—number of rows of kernels. This maximum girth aspect for the corn is determined at V5 to V6 growth stage—8 to 12 inch tall corn.

From the maximum girth potential, the actual girth will be influenced by the weather, the nutrient status, and the plant energy supply.

Individual ears will always have even numbers of rows, but a population of ears can have any number of rows. As you increase the average ear girth from 15 rows to 16 rows, yield will increase by 7 to 10 Bu/A.  In my 111 day corn, I am finding 18 and 20 rowed corn.

Today, July 22, I looked at 111 day corn with brown silks in both corn-on-corn and corn-on-soybean ground. The girth aspect for both ears was excellent with 18and 20 rows around, but the corn-on-corn was exhibiting some unfilled ovules while the corn-on-soybean was entirely filled.

Observations

In an area where water moved across the field after heavy rains, the corn has a higher level of leaf firing than the adjacent area where no water flowed across. The area where the water flowed across the soil was more saturated and had a higher level of nitrogen loss.

Some of the late April planted corn is beginning to tassel this week, July 8-12.

Generally, 60 days after tasseling, corn will have reached physiological maturity. Physiological maturity doesn’t mean that the corn is harvest ready; it means that the maximum dry matter level has been reached in the kernel—black layered—and grain moisture is approximately 32%.

Observations

Corn

Corn planting depths of less than 1.5 inches are creating significant growth and nutrient uptake problems in our fields. The corn needs to be planted 2.0 inches deep. Where the corn is planted 1.5 inches or less, the corn is having problems developing a good root system and has a higher incident of seedling blight and dampening off and the crown rots are more developed. In addition, both N and K (potassium) uptake is decreased.

Soybeans

We are beginning to find that pod development is occurring on our soybeans.

The Japanese beetles are beginning to feed on the soybean leaves. The economic threshold level is currently 30% defoliation on the entire plant.

If you are applying a late herbicide or an R₃ fungicide application, I would encourage you to kill the Japanese beetles now.
 
          

When will this year’s corn tassel?

Many have heard the old saying “knee high by the 4^th of July.”

Last year, my 111 day corn was tasseling on July 1, but this year’s corn was planted 5 days later, April 29 & 30, and our daily temperatures have been cooler—fewer growing degree days—resulting in a later tasseling date.

I would look for this year’s corn crop to tassel in the last three weeks of July, 10-31. With this extended tasseling period, the silk clipping insect could be a real problem.

Observations

For the first three weeks of June, the Agronology 10 test plot received only 0.8 inches of rain, but since early Monday morning through Wednesday morning this week, the plot has received almost 3.5 inches of rain.

On May 18, I observed my first flowers on our soybeans—planted May 1, 2013.

Soybeans are photo period sensitive plants, meaning that they transition from their vegetative phase to reproductive phase in response to this shortening of day length. Summer solstice, June 21, is normally the longest day in hours of daylight for the year.  After June 21, day length will decrease about 3 minutes per day.

Observations

• Corn varieties are making a huge difference in plant height, root growth, nutrient uptake levels and plant color.
• Those “wet areas,” which were continually wet, certainly have made a significant impact on this year’s crop.
  • The crop stands are reduced, plant height and development is retarded, and root development is restricted.
• Soil compaction is omnipresent this year.
  • This compaction can be found as a sidewall compaction created by the planter unit, or the compaction can be found as a uniform compaction zone created by secondary spring tillage. In both cases, the largest impact is on root development and plant growth.
• Planting depth for corn has been a major problem this year.
  • Those planting depths for corn of 1.25-to-1.5 inches are generally the worst. The 2.0 inch planting depths are looking significantly better. The greater planting depth is allowing the nodal root system to develop more dynamically.

As summer arrives on June 21, 2013, I am observing a phenomenon occurring in some of our corn fields.

Observations

The event I am seeing is that the last emerged corn leaf is light green or almost white colored. The cause for these light colored leaves is good growing conditions for the plant.

The light colored leaf has emerged prior to full development of the chlorophyll in the leaf. After a day or so, the chlorophyll will fully develop and then the leaf will turn green.

The condition of the year’s corn crop varies from looking good to drowned out. Many of the growth problems are associated with the amount of rainfall received and the drainage for each field; the better the drainage, the better the crop appearance.

Observations

During May 2013, the Ag 10 Research Center received 8.75 inches of rain, which is twice the normal amount for May. In the more poorly drained areas, the corn height is significantly shorter—one growth stage smaller—and the color of the corn is a lighter green. There are two principle reasons for these observations.

First, the applied N has moved out of the current rooting zone for the corn crop due to this excessive rainfall.

Secondly, the nodal root system, the principle root for the corn plant, is smaller than normal and reduced nutrient (N) uptake is occurring. This reduction in root growth is caused by cool weather, too much water, lack of oxygen in the root zone, and the lack of nutrient uptake (N, K, and S).

Results

This is possibly a good season to strongly consider a sidedress application of 30-to-50 lbs. N/A. I would suggest the following N sources be considered:

• 20-0-4-2
• Nitrogen plus sulfur.
• 32% UAN.

For some farmers this year, 2013, “Prevented Planting” is a reality. What are my options after discussing the situation with my insurance agent?

Prevented Planting Options

• Plant soybeans on those corn prevented planted acres.
  • This will dramatically reduce the corn root worm presence.
  • This will reduce N requirement by 40-to-50 lbs. N compared to continuous corn recommendation.
  • However, it may not be possible due to previously applied corn herbicide.
  • It is important to review the economics for late-planted soybeans. It may not justify the risk.
• Plant nothing on the prevented planting acres.
  • This is low-cost, but you may need to perform tillage to control weeds.
  • An additional concern could be that with no crop on the acres, there is the loss or reduced amount of VAM (vesicular arbuscular mycorrhizal fungi) present to assist in next year’s phosphorus uptake. The VAM fungi assist in increasing phosphorus uptake for the plant.
  • This gives the possibility for increased soil erosion.
  • This has no N credit.
• Plant a cover crop on the prevented planting acres.
  • For June-July planting period, warm season grasses like:
    • Sorghum.
    • Sorghum-sudangrass.
    • Millet.
    • Note: Check the previous herbicide plant back restrictions for the warm season grasses.
  • For August-September planting period:
    • Spring oats.
    • Winter wheat.
    • Annual rye grass.
    • Red clover.
    • Tillage radish.
    • Alfalfa.
    • Cereal rye.
    • Winter triticale.

Now is the time to consider a post N application.  Our corn is planted and a significant rain event occurred over the Memorial weekend.  This rain event has possibly moved the applied N deeper into our soil.  With this deeper movement of the applied N into the soil, the amount of root available N currently is decreased.

What can be done?

1. 
    Nothing – hope the roots find the displaced N
2. 
   Post apply some more additional N as:

1. 
   32%
2. 
   Nitrogen plus sulfur
3. 
   Apply 20-0-4-2_s (Nitrogen-Phosphorus-Potassium-Sulfur)