Friday, August 30, 2019

Yield and Quality of July Planted Corn

The Kernels
  • Corn has two peaks in forage quality: one at pollination and one at 50% kernel milkline.
  • Bareness generally reduces yield and grain content resulting in increased fiber content, but this is often accompanied by lower lignin production that increases fiber digestibility. Also, the forage has higher sugar content, and higher crude protein than normal corn silage.
  • Relatively small changes (5 to 8% decrease) in forage quality (Milk per ton) occurs with July planting dates compared to corn planted April 28 to June 1.
  • Milk per acre of July planting dates decreased 17 to 92% to levels ranging from 2,300 to 24,000 lbs milk/ A. 

Record high prevent plant acreage occurred in 2019. In July, many acres were planted to cover crops, including corn (Figure 1). Due to low forage inventories, USDA-RMA allowed cover crop acres to be harvested for silage.

Figure 1. Prevent plant acreage in 2019. Data source: Farm Bureau and USDA-FSA.

Corn has two peaks in forage quality: one at pollination and one at 50% kernel milkline. Forage quality as measured by Milk per Ton is high during vegetative phases prior to flowering. Like all forages, quality decreases after flowering. Unlike other forages, quality improves beginning around R3. The early peak in forage quality at pollination is high in quality but too wet for ensiling. The later peak is more familiar and is the one we typically manage for when producing corn silage because it maximizes both biomass yield and quality.

If pollination is unsuccessful, the forage quality following the first peak does not change and will continue to remain high due to higher sugar content (water soluble carbohydrates), higher crude protein, higher crude fiber and more digestible fiber than normal corn silage. Unsuccessful pollination (bareness) generally reduces yield and grain content resulting in increased fiber content, but this is often accompanied by lower lignin production that increases fiber digestibility.
If pollination is poor yet some kernels are developing, the plant can gain dry matter and farmers should wait with harvest.

Harvesting and Handling Barren Corn
The harvesting challenge is that green, barren stalks will contain 75-90% water. Barren corn is difficult to harvest because it is rank and too wet for silage storage structures. Arlington UW-ARS staff have had some success using a discbine to cut barren corn into a windrow. The windrow would need to dry to desiccate the forage. A forage chopper with a hay pickup attachment is then used to gather and chop the windrow into a wagon for transport to a storage structure for ensiling.

Grazing is an option but be careful about nitrate toxicity problems. If grazing, consider potential for nitrate toxicity. This is especially likely to be a problem if growth was reduced to less than 50% of normal and/or high levels of nitrogen were applied.

If the decision is made to harvest the crop for ensiling, the main consideration will be proper moisture for storage and fermentation. The crop will look drier than it really is, so moisture testing will be critical. Be sure to test whole-plant moisture of chopped corn to assure yourself that acceptable fermentation will occur.

Forage quality of barren and poorly pollinated corn
Coors et al. (1997) evaluated the forage quality of corn with 0, 50 and 100% pollination of the kernels on an ear during 1992 and 1993. These plots were harvested in September.

A typical response of corn to stress is to reduce grain yield. Bareness reduced whole-plant yield by 19% (Table 1). Kernels on ears of 50% ear fill treatments were larger and tended to more than make up for reduced numbers (Albrecht, personal communication). With the exception of protein, as ear fill increased, whole-plant forage quality increased.


Table 1. Forage yield and quality of corn with differing amounts of pollination (n= 24; 1992 and 1993).

Yield and Quality of July Planted Corn
We conducted experiments during 2005 and 2006 to determine what could be expected by planting corn in July. Three corn hybrids (brown midrib, full-, and shorter-season) were planted on five different dates from April 28 to August 1 at Arlington, WI. The 2005 growing season had a killing frost on October 26, which was three weeks later than normal.

Seasonal dry matter production after planting during July ranged from 0.7 to 7.5 Tons DM/A while the same hybrids planted April 28 to June 1 produced 8.7 to 10.0T DM/A (Table 2). Milk per acre is significantly lowered 92 to 17% to levels ranging from 2,300 to 24,000 lbs milk/ A for planting dates in July. Crude protein, NDF and NDFD increased with later planting dates. Although, little starch content was measured in later planting dates, overall milk per Ton tended to decrease slightly. Thus, relatively small changes in Milk per ton occurred during planting dates in July with levels ranging from 2800 to 3200 lbs milk/T, which was a 5 to 8% decrease from corn planted April 28 to June 1.

 Table 2. Corn forage yield and quality response to July planting dates.

Corn can produce significant dry matter yield when planted during July, but the amount produced depends upon when a killing frost occurs. Growers need to check on options available from their insurance companies before taking action and planting corn in late June and July for emergency forage. Herbicide labels must be adhered to before switching to other crops.

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Thursday, August 29, 2019

The “Normal” Pattern of Corn Forage and Grain Development

The Kernels
  • Corn exhibits a “double peak” for corn silage quality during its life cycle with the first NDFD peak at R1 and the second starch content peak at R5.5.
  • Corn as a forage crop reaches maximum yield and quality values at nearly the same time (R5.5).
  • At harvest (R5.5), the wettest plant part is the lower stalk, while the driest plant part is the grain. Adjusting the cutter bar can change forage moisture 3 to 4% points to better target the recommended moisture for the storage structure.

Corn is a high yielding, high energy, low protein forage commonly used for growing and finishing beef cattle, in cow-calf production systems, for growing dairy heifers, and for lactating dairy cows. Corn grown as a forage and fermented in a storage structure preserves the silage for subsequent feed-out. Understanding yield and quality changes during the life cycle of corn is critical for timing harvest of a field.

The “Double Peak” of Corn Silage Quality
Corn exhibits a “double peak” for corn silage quality during its life cycle (Figure 1). The first peak is related to energy derived from stover fiber (NDFD) and water-soluble carbohydrates, while the second peak is derived from NDFD and starch content of grain. Forage quality as measured by Milk per Ton is at the first quality peak just prior to silking (R1). Like all forages, Milk per Ton decreases following flowering (VT-R1). Unlike other forages, corn silage Milk per Ton after the kernel blister stage (R2), steadily increases to a maximum second quality peak around 50% kernel milkline development (R5.5) due to grain yield development.

Forage yield and Milk per Acre

One of the unique aspects of corn as a forage crop is that yield and quality reach maximum values at nearly the same time. Forage yield increases steadily through its life cycle. At R1 all the plant photosynthetic “machinery” is produced on the plant. For most hybrids grown commercially in Wisconsin the grain filling period (R1-R6) is about 55-60 d. Following pollination, grain develops in a sigmoidal fashion with a 7-10 d lag period, followed by a 40-44 d linear phase, and ending with a 7-10 d maturation phase. Starch content increases as grain develops and matures.

Multiplying corn forage yield by Milk per Ton results in Milk per Acre. Milk per acre peaks at R5.5. Then due to leaf senescence and loss, yield and quality tends to decrease slightly.

Using Forage and Grain Moisture for Harvesting
At some point forage yield is no longer as important as timing harvest at the correct moisture for the storage structure to ensure proper fermentation and preservation. The wettest plant part on corn is the lower stalk, which is also of poor quality (low NDFD) and is high in nitrates. The driest plant part is grain. By raising the chopper cutter bar 12 inches, forage moisture decreases 3-4% points. Also, the wettest, poorest quality plant part is left in the field. Forage yield is decreased about 10 to 15%, but forage quality increases 8 to 12%, so that overall Milk per acre is only reduced about 3 to 4%.

The effect on forage moisture is significant when the field is scheduled to be harvested by a custom chopper. By adjusting cutting height, the operator can better achieve the optimum moisture for the storage structure. About a one week shift in harvest timing can be achieved (assuming 0.5% per day drydown rate).



Figure 1. Normal Pattern of Corn Forage and Grain Development in Wisconsin.

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Wednesday, August 28, 2019

Corn Plant Population: The second most important management decision for moving off the yield curve

The Kernels:
  • Farmers are increasing plant densities (PD) in commercial fields. 
  • The economic optimum plant density (EOPD) is lower than the plant density required to maximize grain or forage yield (MYPD). 
  • The economic optimum plant density is likely different between farms and fields within farms.
  • To move off current yield levels, begin by planting a field to what you think is the optimum plant density and at two or three places (rounds) in the field, increase plant population by 10%.

Farmers are increasing plant densities (PD) in commercial fields (Figure 1).  In research plots, the plant density that maximizes corn grain and silage yield has been increasing through time. The economic optimum plant density (EOPD) is a function of corn yield and quality responses, seed cost, and grain or silage price. The economic plant density is lower than the plant density that maximizes yield (MYPD).


Figure 1. Corn plant density of farmer fields since 1982. Data source: USDA-NASS.

Farmers have many questions including: What is the maximum yield PD (MYPD)? What is the economic optimum PD (EOPD)? Is the MYPD and EOPD the same for silage and grain? Do hybrids differ for MYPD and EOPD? Do fields differ for MYPD and EOPD? How does yield risk change with increasing plant density? How does drought affect MYPD and EOPD? Is lodging and barrenness affected by plant density? How should variable rate technology in precision farming systems be adjusted in-field?

Since 1997, plots have been that are 8 rows wide by 25 feet long. Four rows are harvested for silage and the remaining 4 rows are harvested later for grain. The target plant densities have varied by year and ranged from 14 000 to 56 000 plants/A. Adapted, high-performing hybrids were selected using results from the UW Corn Trials and varied for relative maturity (full- and shorter-season). Milk per Ton and Milk per Acre were estimated using Milk2006. The treatment (hybrid x plant density) mean that maximized the measure within a year was set to 100%. The results in Figure 2 were summarize the relationship between various measures and plant density across all experiments conducted between 2008 to 2017.

Maximum grain yield was measured at 41 000 plants/A. The relationship increased to a maximum and then decreased as plant density changed. In agronomic research, it is very difficult to measure grain yield differences less than 5%. So, grain yields within 5% of the maximum grain yield were measured at plant density above 30 000 plants/A. The economic optimum plant density (EOPD) was 35 000 plants/A. The EOPD was within 95% of the maximum at 26 000 plants/A.

Maximum forage yield was measured at 48 000 plants/A and was within 5% of the maximum when plant densities were above 35 000 plants/A. Forage quality as measured by Milk per Ton decreased linearly from a maximum at 18 000 plants/A, but was within 5% of the maximum across the range of plant densities measured. Maximum Milk per Acre was measured at 45 000 plants/A and was within 5% of the maximum at 32 000 plants/A. These results are a good example of the trade-off that exists between forage yield and quality, i.e. the plant density that maximizes Milk per Acre is intermediate between plant densities that maximize forage yield and Milk per Ton.

Plant densities that maximize grain and forage yield are higher than currently recommended plant densities. These results indicate that the plant density that maximizes forage production is about 7000 plants/A higher than the plant density for maximizing grain yield. The economic optimum plant density is lower than the plant density required to maximize grain or forage yield. The economic optimum plant density is likely different between farms and fields within farms.


Figure 2. Relationship between corn plant density and grain yield, economic optimum (AGI), forage yield, Milk/Ton, and Milk/Acre. Data source: Lauer (Arlington 2008-2017).

Adjusting plant density is probably one of the best ways to move off current yield levels. Begin by planting a field to what you think is the optimum plant density and at two or three places (rounds) in the field, increase your population by 10%. For example, if you currently plant at 30 000 plants/A, do so for the majority of your field, but in two or three rounds increase the population to 33 000 plants/A. Measure yield at the end of the season and during the season watch for "runt" plants, tillering, prolific versus ear bareness on plants, big versus small ears, ear tip "nose-back" and plant lodging. Adjust the field accordingly the following year.