Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


Printer Friendly Version

September 6, 2013



Much of the area has received little to no rain since late July. It is easy to see differences in soil type again this year, with both corn and soybeans being dead or near death on the soils with poor moisture holding capacity and crops still hanging in there on the better soils. With the late soybean planting and little to no rain in August in some areas, I would normally think that soybean yields will be very poor. However in looking at fields on the better soils, it does look like the soybeans podded very well and there may still be potential for decent yields in some fields. I think the cooler than normal weather from about July 23 to August 20 has really helped to reduce the yield losses we would have seen if the temperatures would have been normal or above normal. Low disease and insect incidence in most fields should also help to reduce yield losses. Soybeans are starting to turn on the early May planted fields, and are turning prematurely from drought stress on later planted fields. Most soybeans are now at or close to R6 (full size beans). It normally takes about 18 days for beans in R6 to reach R7 (beginning to turn and safe from frost).


Corn yields, and grain moisture content will likely be extremely variable again this year. Most fields in the area are in the dent stage now, with those that are not already dead from the drought needing at least a couple more weeks to reach maturity. It is very difficult to estimate soybean yields, so don’t think we’ll know what we have until the combines start to roll. Corn yields are fairly easy to estimate just by counting ears and kernels, but kernel size will likely be variable this year depending on how severely fields are hurt by the drought, making yield estimates more tricky. Usually we assume 90,000 kernels per bushel, but it might be wise to assume 100,000 or more kernels per bushel, especially on fields hard hit by the drought. To estimate yield, count the number of ears along a row per 1/1000 acre. Select several ears at random (I close my eyes to select ears so I’m not biased). Count rows of kernels and kernels per row.


[(number of ears per 1/1000th acre) x (number of kernels per row) x (number of rows of kernels)]/90= bushels per acre (use 100 or more to divide by if kernels are small)


Ear population per 1/1000th acre:

26 feet 2 inches for 20-inch rows

23 feet 9 inches for 22-inch rows

18 feet 8 inches for 28-inch rows

17 feet 5 inches for 30-inch rows

14 feet 6 inches for 36-inch rows

13 feet 9 inches for 38-inch rows




From Brian Lang:


Tips on Moisture Determination

Here is a short article from the University of Wisconsin on whole plant moisture variability in the field, desired moisture for various storage structures, and procedures for moisture determination of corn silage.


Other Tips on Corn Silage Harvest

The following is an article from the University of Minnesota that summarizes many aspects of corn silage harvest.  Author: Jeff Coulter, UMN Extension Corn Agronomist. 

“Harvesting High Quality Corn Silage”


Proper harvest management is critical for high-quality corn silage, and it starts with harvest timing. This ensures that the harvested crop is at the optimum moisture for packing and fermentation. Silage that is too wet may not ferment properly and can lose nutrients through seepage. If silage is too dry when harvested, it has lower digestibility because of harder kernels and more lignified stover.  In addition, dry silage does not pack as well, thus increasing the potential for air pockets and mold.  Optimum silage moisture at harvest ranges from 50-60% for upright oxygen-limiting silos, 60-65% for upright stave silos, 60-70% for bags, and 65-70% for bunkers. Due to variability among hybrids and growing conditions, it is necessary to measure silage moisture using a commercial forage moisture tester or microwave oven rather than simply estimating it from the kernel milkline.  Instead, kernel milkline should be an indicator of when to collect the first silage samples for moisture testing.  A general guideline is to begin moisture testing when the milkline is 25% of the way down the kernel for horizontal silos, and 40% of the way down the kernel for vertical silos. Then, assume a constant dry-down rate of about 0.6% per day, and measure moisture again prior to harvest.


Length of cut and crop processing are also important for obtaining high-quality corn silage.  This is because breakage of cobs and kernels increases surface area; which improves digestibility, reduces cob sorting, and results in higher density silage that packs better.  Although crop processors are expensive, the higher-quality silage produced can increase milk production by 300 pounds per cow per year. The benefit of crop processors is greatest when there are harder kernels resulting from delayed harvest or drought. When using a crop processor, chopper cut length can be increased to reduce horsepower requirements while maintaining optimum particle size.  For unprocessed corn, ideal chop length is 0.375” theoretical length of cut.  For processed corn, recommended settings are a 0.75” theoretical length of cut with 0.08 to 0.12” roll clearance.


A 4 to 6” cutting height is generally recommended for corn silage, as it maximizes silage yield and milk per acre. However, drought-stressed corn can accumulate nitrate in the lower part of the stalk, thus increasing the potential for nitrate poisoning, particularly in older livestock on lower-energy rations. The potential for high nitrate silage can be even worse if drought-stressed silage is harvested within 10 days of rainfall, since rainfall increases crop uptake of soil N.  Silage with high nitrate levels can be managed by dilution with other feeds or by increasing the cutting height to 12”. Silage cut at this greater height has been shown to have 8% less silage yield and 2% less milk per acre. This same study found that a cutting height of 18” resulted in 15% less silage yield, 12% greater milk per ton, and 4% less milk per acre when compared to a 6” cutting height.  Increased silage quality with high cutting is due to a higher ratio of grain to stover.  However, corn stalks are a good source of fiber and the lower tonnage with high-chop silage typically makes it difficult to justify in the absence of high nitrate levels.  When harvest begins, fill silos rapidly to reduce exposure of silage to oxygen and to reduce fungal growth. For bunker silos, pack silage as tightly as possible in progressive wedges in depths of 6” or less.



Lauer, 2003.

Roth, 2003.

Schroeder, 2004.


Calculating a Value for Corn Silage in the Field

Questions often arise this time of year about how to arrive at a fair price for standing crops such as corn silage, oats, hay, and cornstalks.  Although there are no widely quoted market prices for these crops, they can be valued according to their relative feed value and compared to some crop that does have a known market price, such as corn grain or baled hay.  Corn silage can be valued most easily according to the price of corn grain. Taking into account the value of the grain, the extra fertilizer cost, and the harvesting costs saved, a ton of corn silage in the field is worth about 6 times as much as a bushel of corn. Use the local harvest price as a guide.  If the current market price is below the county USDA loan rate, use the loan rate instead.  For example, if expected corn price is $4.50 per bushel, the value of standing silage is $4.50 x 6=$27 per ton.  Assuming a corn silage yield of 18 tons per acre, the value of standing corn is $27 per ton x 18 tons =$486 per acre.  This price assumes silage is harvested at 60 percent moisture.  To adjust for other moisture levels, subtract the actual moisture level from 100, divide by 40, then multiply by the estimated value for 60 percent moisture silage.  For example, the silage moisture level is 70%.  Silage dry matter level is 100% - 70% = 30%.  If the silage value at 60% is $27 per ton, then the silage value at 70% is $27 x 30/40 = $20.25 per ton.


Similar types of calculations are used to price hay and corn stalks and can be found in ISU Extension Farm Management fact sheets:

1)  Pricing Forage in the Field:

2)  Estimating a Value for Corn Stover:


For another option on pricing corn silage, the University of Wisconsin just updated there guidelines.  This is available at:




Soybean Aphid Numbers Increasing, But Still at Low Levels


I’ve been seeing soybean aphid numbers increasing in the area in the last week, so we need to continue to watch for this pest for a while longer. Hopefully the excess heat that is forecast for the next week will reduce their reproduction rate and the numbers will start to decline naturally soon. Brian Lang reports that the numbers have peaked in some fields in NE Iowa and now declining, so hopefully we can escape this threat this year.





From Brian Lang:


Fall Harvest


This time of season there are always questions on when that last cut could be made and still allow enough time to build root carbohydrate before the killing frost.   The answers to these questions are usually something like… “its fine to harvest through the first week of September”, and… “we recommend harvesting at least 6 weeks before the killing frost”.  On average, a typical killing frost (25oF) in northeast Iowa occurs in the third week of Oct.


While those “good old answers” still work, the more correct answer actually deals with growing degree days (GDD), not the calendar.  Researchers now define a risk assessment of fall harvest based on alfalfa GDD.  The research basically says as long as the plants accumulate at least 500 GDD from harvest to killing frost, it will have stored enough root carbohydrate to survive the winter.  A nice summary of this research is available at the following web site.  The data from Lancaster and Beloit, WI (southern WI) would apply quite nicely to northeast Iowa.   The Lancaster & Beloit data suggest alfalfa harvested through the first week of September is very low risk of winter injury, having plenty of time to replenish root carbohydrates going into the winter.  A September 15 harvest could start providing some risk, and a September 21 harvest even more risk.  These risks do not mean that you will lose the entire stand, but rather would likely lose a percentage of plants and reduction in first crop yield next season because of winter injury and slowed plant recovery in spring.


What if you chose to harvest “after the killing frost”?  This research says as long as the plants do not accumulate more than 200 GDD from after harvest to before the killing frost, the plants should still overwinter just fine.  This means that you do not have to wait for the actual killing frost to occur as long as you are close to it when you harvest.  i.e. Oct. 15 is a good cut-off date where if the killing frost has not occurred yet, it likely will soon, and the weather in late Oct. is usually cold enough that 200 GDD will not accumulate in the time remaining in the fall.  A critical issue with harvesting after a killing frost is that little to no regrowth will occur following the harvest, so you want to cut high, leaving a good stubble height (~6 inches) to help trap snow and insulate the plants.




Tuesday, September 10 - 5:00 p.m.


Cover Crops Field Day – Jim Meade Farm West of Iowa City


A rye cover crop will be seeded into soybeans at the site of the field day. Local farmers with experience with cover crops will discuss their experiences.  One producer who will be sharing his expertise is Steve Berger. Berger has been seeding cover crops for over 20 years on his farm near Wellman. There will also be information available from the NRCS on cost share funds available for seeding cover crops. Seed salesmen and aerial applicators will also be attending the event. The Jim Meade farm is located at 2331 340th St. SW, Tiffin (about a half mile south of I80 and 1.5 miles west of the Tiffin exit). A free meal will be provided by the Johnson County Cattleman’s Association, courtesy of Iowa Farm Bureau.


Thursday, September 12 – 1:30 p.m.


Fall Field Day at ISU SE Iowa Research Farm – Crawfordsville


Sarah Carlson, a cover crop specialist with Practical Farmers of Iowa will present "Are Cover Crops for You?” at one of the stops on the field day tour.  Other topics on the tour will be “Bioenergy Crop Research” by Greg Brenneman, ISU Extension Ag Engineer, “How to Slow the Spread of Pesticide Resistance” by Mike Owen, ISU Extension Weed Specialist, and “Dry Corn in the Field or in the Dryer?” by Jim Jensen, ISU Extension Farm Management Specialist. CCA credits will be available for a fee.



If you have any questions, please feel free to contact the Iowa State University Extension Office.

maroon ball East Central and Southeast Iowa Crops Home Page maroon ball ISU Extension and Outreach maroon ball ISU maroon ball ISU Extension Agronomy maroon ball ISU Agronomy
maroon ball Calendar maroon ball Search maroon ball Jobs maroon ball Feedback maroon ball Internet Resources maroon ball State Extension Sites in Other States maroon ball Local Extension Offices in Other States maroon ball ISU Extension and Outreach Policies

Last Update: September 6, 2013
Contact: Jim Fawcett

Nondiscrimination Statement and Information Disclosures