Hybrid Maturities

Corn hybrid maturity ratings can be confusing to farmers and Ag professionals. One of the causes for this is that maturity can mean different things to different people.

Agronomists and plant breeders talk about corn maturity and think about the end of the grain fill period. This is the point when kernel weight has reached its highest point for the crop. Another term that is used interchangeably is “physiological maturity”. Another term that may be more commonly used is to say the crop has reached “black layer”, because an actual black layer develops at the tip of the kernel.

Grain moisture at this stage can be anywhere from 25 to 40%, and is typically in the mid 30%. It varies from hybrid to hybrid and year to year because of growing conditions in the season.

Most growers think of maturity in terms of “harvest maturity”, or when the crop can be harvested with minimal kernel loss or damage, and minimal drying expense. Usually growers like to see this harvest moisture around 25% or lower, depending upon whether the crop will be stored and fed for high moisture grain or marketed as dry grain.

Traditionally corn hybrids have been rated by seed companies on days to maturity, such as a 98 day hybrid for example. This method of rating hybrid maturities compares new hybrids to other hybrids of known maturity based on their grain moisture content at harvest time. The normal standards are that a hybrid will have a dry down rate of about 0.5 percentage points per day, so if the new hybrid has grain moisture 4% over a known hybrid that is rated as a 90 day hybrid, the new product would be rated as a 98 day hybrid (4 points moisture divided by 0.5 points per day moisture loss equals 8 days). It’s important to keep in mind that this system uses some assumptions about average grain drydown and normal growing conditions, as we well know from this last season, not all years are normal growing seasons.

Another method used to express relative maturities considers heat units, often referred to as growing degree days, or growing degree units. This method takes into consideration the amount of heat accumulated of a specific period of time. It is based on actual temperature measurements and not based on comparisons to other hybrids. Trelay has corn hybrids that range from 2150 to 2925 growing degree units in our product line-up.

The correlation between the two systems is close but not identical. Neither method is perfect because they are influenced by the environmental factors of the growing season, and plant stress on plant maturation such as moisture and or drought as a couple examples. Another factor to keep in mind is that not all seed companies use the same method for hybrid maturity evaluations. Some count days from planting, and some count days from crop emergence, so there can be some variation between two seed companies that are both selling products that are marketed as 98 day hybrids.

So what does this all mean to you? This is just one more reason you need to do some research before making decisions on hybrids. Be careful not to make decisions based on a single plot or test location. The more plots and yield info that you can compare across several sites and multiple years will give you a much better idea of how a specific hybrid will perform on your farm. Your local Trelay Rep will be able to help supply you with much of this information to partner with you and help make the best decision for your farm.

2009 Harvest Results

Harvest results are steadily streaming in...I've added links to Trelay's corn and soybean harvest results under My Favorites.  New data is posted daily, so check back often. 

Corn Test Weights

Corn test weight is a popular topic this year. It is a volumetric measurement; the official definition is “the amount of grain contained in 1.244 cubic feet of space”. The US Grain standard is 56 lbs. per bushel for No. 1 yellow corn, and 54 lbs. per bushel for No. 2 yellow corn. This weight is contingent on moisture content; the normal standard use in the grain industry is 15% or 15.5% moisture. I’m not sure how this system started hundreds of years ago, but my guess is that it was used because scales were not as accessible as today and it was just easier to measure the amount of grain in a wagon or corn crib than to actually take it over a scale.


Many growers associate high yields with high test weight grain, and low yields with lower test weight grain. The truth is that there is very little relationship between yield and test weight. We often see the same test weights across high-yielding and low-yielding environments. Higher test weights will allow you to get more lbs. of grain in a given volume of space, such as a truck or a bin.


What influences test weight?


The physical characteristics of the kernel, such as size, density, shape, and texture of the kernel surface, all come into play. Grain moisture is the most important factor to influence test weight. As grain dries down, it also shrinks, allowing more kernels to fit into a given space or bushel, in this case. This fall, we are seeing corn wetter than we have in many years, so it stands to reason that we will see lower test weights because of the higher moisture.


How much test weights will increase after grain drying varies based on hybrid genetics, condition of the grain, and the temperature that is used to dry it. The following table shows some general guidelines to use for calculations.

Some other factors that influence test weights are: 1) plant stresses during grain fill that could include disease, 2) ear rots and molds, 3) insects, 4) soil or fertility conditions, 5) hail damage, and 6) like this year, in many areas, frost hits before corn reaches Black Layer. Any of these events can disrupt the movement of nutrients and sugars to the kernels.


What if my corn didn’t make it to Black Layer?


Black Layer or physiological maturity signifies the end of nutrient accumulation in the kernel. If corn freezes before it reaches this stage, we can expect lower test weights. The University of Minnesota conducted a study on drying immature corn a few years ago. Their results are listed below (KM = kernel moisture, TW=test weight).

In this study, corn that was in the soft dough to early dent stage actually decreased in test weight after drying. Immature corn that was well dented to Black Layer all increased in test weight to nearly 56 lbs./bu after drying.
Once again, in a year like we have just seen, we can expect to see lower test weights because of higher grain moistures. The good news is test weights will most likely increase after drying, but the amount of increase will vary between varieties and their stage of development of the corn at the time of frost.


References:


Hicks, Dale. 2004 Corn Test Weight Changes During Drying. Minnesota Crop News. http://www.extension.umn.edu/cropenews/2004/04MNCN29.htm
Nafzinger, Emerson. 2003. Test Weight and Yield: A Connection? The Bulletin, Univ. of Illinois Extension. http://ipm.illinois.edu/bulletin/pastpest/200323h.htm
Nielson, R. L. 2009. Test Weight Issues in Corn. Corny News Network. Purdue University Dept. of Agronomy. http://www.agry.purdue.edu/Ext/corn/news/timeless/TestWeight.html
Rankin, Mike. 2009. Understanding Corn Test Weight. University of Wisconsin Extension Publication.

Silage Harvest Update

Silage harvest is done in most areas. I have been getting many forage samples back and have been very impressed with what I am seeing this year. Silage yields are down in tonnage for central and northern Wisconsin, in the areas hurt by the dry weather earlier this year, but quality seems to very good yet. The rest of the areas are reporting big yields and high quality. Silage yields are running in the high 20’s to low 30’s for tonnage to the acre. Our new full season hybrid we added this year even bumped 40 ton to the acre in one plot!! Now that’s a lot of corn. This variety also produces good grain yields so the starch levels in the feed sample have been good. A couple earlier hybrids that we added are also doing great, we have a new 104 day and 107 day hybrid that both came back with great tonnage yields and starch levels in the high 30’s, a dairyman’s dream.

Early Frost?

What a year, we go from one of the nicest Septembers with 80 degree weather and great growing conditions to high temps in October that are 20 degrees below normal. Most areas saw the first frost over the weekend. So what will this do the corn that has not reached black layer yet? Blow is a chart that shows what the kernel moisture is typically at different growth stages of the plat, along with the yield loss that could be expected with frost at that time.

This does a nice job to explain what we may see in the field if you find yourself with corn that has not quite made it to the finish line. The good news is that early grain harvests are coming in better than we expected for the year. Some yield results are running well over 200 bushel an acre, and even over last year’s numbers! Have a great harvest season, and look back for more yield updates as they com in.

Plot Tours - 3rd Week of August

This past week I had the opportunity to travel to many of our local plot and field days. I was impressed with how Trelay’s crops looked overall. In north central and north eastern Wisconsin the crop shows some stunting from the dry weather, but the rains came in time to produce some good grain yields. Many varieties are just getting to hard dent and have a ways to go before they reach black layer, but the warm September weather is just what we needed to finish this crop.

When the corn is at full dent, the kernels are about 1/4th milk and approximately 3 weeks to black layer or physiological maturity. Silage harvest has begun in many areas with whole plant moisture running in the low 60% to over 70%. Dry matter accumulation of grain is about 75% at 1/4th milk line and about 90% at ½ milk line.

With large acres affected by the hail storms this year, growers need to be concerned with molds that may be present in their fields this fall. These molds can cause the development of mycotoxins which need to be tested before the grain or forage is fed. As long as the concentrations of mycotoxins are known, the feed can be fed safely, although it may need to be blended with other feed stuffs. Different classes of livestock have different levels of sensitivity to mycotoxins, so consult your nutritionist before feeding any hail damaged crops that may contain mycotoxins.