Corn Harvesting - Corn silage

Part 1, Section 4: Corn

Corn

HARVESTING

Corn silage

One of the most important steps in producing quality corn silage is to harvest at the proper moisture for the storage structure. Desired moisture levels for different structures are as follows: for sealed airtight silos, 60 to 65 percent; for upright silos, 63 to 68 percent; and for trench silos, 65 to 72 percent. Ideally, moisture levels in the silage should be monitored at harvesting to prevent harvesting the crop outside the desired range. If moisture testing is not feasible, then you can estimate crop moisture by the stage of crop development.

Figure 1.4-3. Kernal milk line showing seperation between firm starch and milky starch.

As kernels start to dent, a separation between kernel starch and milk can be seen. The firm starch is deposited in the crown (outer) area of the kernel and the milk occupies the basal area of the kernel (Figure 1.4-3). A whitish line appears, separating the two areas. As the crop matures, this kernel milk line moves down the kernel, and whole plant moisture declines. When the milk line reaches the base of the kernel, a black layer forms and the crop is physiologically mature.

Recent research has shown the kernel milk line to be only a rough indicator of corn silage moisture levels. On the average, silage moisture levels will be about 70 percent at full dent, when the milk line first appears, and will fall to 60 percent at physiological maturity (black layer) (Table 1.4-11). There often is considerable variation between years, however, and when conditions have been particularly dry or wet for several weeks prior to harvest, the moisture can be as much as 5 percentage units different from that predicted by the milk line. When this line reaches the midpoint of the kernel (half milk line), silage yields reach a maximum and the crop moisture level should be near 65 percent. At this point, the stover part of the plant has good digestibility, and the moisture is at the desired level for storage in airtight silos.

Table 1.4-11. Whole plant moisture relative to stage of kernel development.
Stage	Moisture %
Full dent	72–68
Half milk line	68–62
Black layer	60–50

One strategy for timing corn silage harvest is to chop a sample at the full dent stage, just as the milk line appears, and determine the moisture content. Then estimate the harvest date for the field using a typical drydown rate of 0.50 to 0.75 percentage units per day.

Harvest considerations also should focus on obtaining the correct particle size distribution and the need to process the crop. Processing silage refers to putting the chopped material between two rollers that are installed in the harvester to crush the harvested material as it passes through. Kernel processing units are becoming more popular on corn silage harvesters in Pennsylvania. Kernel processing has the advantage of crushing cob slices and kernels, and it can increase the starch availability in the silage by about 10 percent. In some cases, this has resulted in increased milk production compared to unprocessed silage. A good general recommendation for the theoretical length of cut (TLC) for processed silage is ¾ inch with a 1- to 2-millimeter roller clearance.

For unprocessed silage, an average theoretical length of cut should range from 3⁄8 to ¾ TLC. Particle size of corn silage should be monitored during harvesting because it can change as crop moisture content varies. The Penn State Particle Size Separator can be used to estimate the particle size distributions for harvested corn silage.

Once harvesting has begun, fill the silo as rapidly as possible and continue until it is filled. Continue to evaluate processed corn throughout the harvest season. Kernels should be broken into multiple pieces, and cobs should be broken into thumbnail-sized or smaller pieces. As the crop matures after half milk line, it may be desirable to have more kernel breakage so that much of the grain is in the bottom pan of the particle size separator.

The most desirable method of packing bunker silos is the progressive wedge method, where silage is continually packed on a 30 to 40 percent grade. This minimizes the surface area that is open to exposure to the air that can result in DM and forage quality losses. If this is not possible, then silos should be packed by spreading relatively thin layers of silage (6 inches deep) and packing it well. If packed well, the silage should have a density of about 14 pounds of dry matter per cubic foot.

Ensiled High-Moisture Corn

The advantages of harvesting high-moisture corn include earlier harvesting, use of longer-season hybrids, and elimination of costs and delays associated with harvesting. Disadvantages include reduced marketing flexibility and higher storage and handling costs.

Any good airtight storage structure can be used—oxygen-limiting silos, conventional upright silos, bags, bunkers, and trenches. An airtight seal over the top is recommended; additional reinforcement may be necessary.
Ear corn must be ground before ensiling to increase compaction and to exclude air. The ideal whole-ear harvest moisture content is 32 percent; the recommended range is between 30 and 35 percent. The lowest moisture level at which to ensile ground ear corn is 28 percent; the upper moisture level is 40 percent. In bunker silos, high-moisture ear corn should be 34 to 40 percent moisture and should be packed thoroughly. The relationship of kernel moisture to total ear moisture is shown in Table 1.4-12. A distributor is recommended for use in upright silos to prevent separation of cob and grain.
Whole, shelled corn should be ground or rolled before ensiling, though satisfactory results can be achieved without grinding or rolling if the grain moisture content is ideal. The ideal kernel moisture is 28 percent; the recommended range is between 25 and 30 percent. The lowest moisture level at which to ensile shelled corn is 25 percent; the upper limit is 33 percent. To prevent feeding losses of undigested whole kernels, grind or crush shelled corn as it is removed from the silo.
High-moisture corn should be ensiled rapidly after harvesting. Loads left overnight or longer will begin to heat and spoil quickly. There is a greater potential for mold growth and for a reduction in the bunk life of the material after unloading.

Ear and Dry Shelled Corn

Ear corn can be cribbed safely when the grain moisture is 21 percent or less. With cold weather and narrow (4-foot), well-ventilated cribs, however, corn may be stored when the grain moisture is several percentage points higher. Monitoring the grain moisture of ear corn is an important management step. Storing ear corn when it is too wet can result in moldy corn and mycotoxin development.
Ear corn yields can be converted to a shelled corn basis using Table 1.4-13. For example, 4 tons (8,000 lbs) of ear corn at 21 percent grain moisture is equivalent to 8,000 divided by 77.60, or 103 bushels of shelled corn.
An important part of the harvesting process is monitoring harvest losses. To estimate ear corn losses, determine the number of full-sized (¾-lb) ears on the ground in 1/100th of an acre. Each of these ears in the sample represents 1 bushel per acre. For 30-inch rows, a 1/100th-acre sample is two rows wide and 87.1 feet long. For 36-inch rows, the same sample is 72.6 feet long.

To estimate shelled corn losses, determine the number of kernels in a 10-square-foot area. Every 20 kernels in this area represents 1 bushel per acre. A useful tool is a rectangular wire frame 30 inches by 48 inches (10 sq ft) that can be carried in the combine and used to measure losses. Be sure to include both ear and shelled corn in your harvest loss estimate. Ear corn losses from in front of the combine (preharvest losses) should be subtracted from your total harvest loss estimate. http://extension.missouri.edu/xplor/agguides/agengin/g01290.htm

Consider the effects of timeliness on harvest losses. Estimates of harvest losses based on long-term average data at Purdue University indicate that losses increase by 1 to 2 percent for each week that harvest is delayed.
A USDA study showed harvest losses increasing three fold from October until December (Table 1.4-14).
Monitor debris and cracked corn in the grain as harvesting progresses. Debris and cracked corn can lower grain quality and increase the potential for spoilage of stored corn.
Shrink factors and discounts used by commercial elevators buying corn vary and will always be higher than the shrink due to moisture alone, to include dry matter losses during handling of the grain. For example, the moisture shrink on an 850-bushel load of corn at 23 percent moisture content (MC) being dried to 15 percent is:

850 × (1 − MC initial/1 − MC final) or

850 × (77/85) = 770 bushels at 15 percent MC

(850 − 770)/850= 9.41 percent shrinkage due to moisture

Using an example commercial shrinkage rate of 1.4 percent per unit of moisture removed would result in a total shrinkage of 11.2 percent, with a resulting net weight of 754 bushels. In this case, the producer would be paid on the basis of 754 bushels.

Drying charges and final moisture contents also can vary. These should be considered in marketing corn. Estimate the net value of your corn, considering discount schedules at several elevators, before deciding where to market wet corn. It is important to realize that the advertised per-bushel price is only one factor influencing the net income from a load of corn. There are no standards regarding shrinkage rates applied to corn. Higher shrinkage discounts essentially translate into a lower per-bushel corn price.

Other potential costs that can be incurred during the marketing process include storage charges or discounts for broken corn and foreign material (BCFM), for foul or musty odors, and for low test weight.