When to harvest 2012 corn silage

Despite variable crop conditions across the state of Michigan, farmers should still harvest corn silage based on whole plant dry matter.

The 2012 growing season has been anything but typical. Across the state, there are really good corn crops, average corn, poor corn and very poor corn crops. No matter what the crop looks like, one thing is the same – it should be harvested between 60-68 percent moisture (32-40 percent dry matter (DM)).

Whole-plant dry matter is the best predictor of when to harvest, not kernel milk line. Digestibility of neutral detergent fiber (NDF) and starch are more closely linked with whole-plant moisture than with kernel milk line. Whole plant dry matter between 30-35 percent indicates the digestibility of NDF and starch is optimal. It is important to harvest when NDF digestibility is high because a 1 percentage unit increase in NDF digestibility is associated with an increase of 0.55 pounds of 4 percent fat corrected milk, according to Oba and Allen, 1999, J. Dairy Science.

Storage type will determine which moisture level will result in optimal fermentation. See Table 1 for moisture/dry matter goals by storage type. If silage is harvested too wet, fermentation will be dominated by undesirable clostridial fermentation which may result in poor animal intake and performance. Silage put up too wet will also seep, leaching valuable nutrients in the environment. If silage is harvested too dry, starch digestibility will be lower, silage will be difficult to pack, too much oxygen will be present and can result in heating and molding of the silage.

Clostridia bacteria are naturally present in the soil. Although their numbers are very low on standing forage, inoculation occurs during mechanical handling of the crop. The bacteria prefer growth conditions that are wet (< 30 percent DM) and a higher pH, although growth can still occur at slightly higher DM and down to a pH of 4.2. According to McDonald, Clostridia bacteria typically take over the fermentation when the lactobacilli have used up available substrate, the silage is wet, and the pH is still above ~4.8.

Table 1. Moisture goals by storage type

Storage type

Moisture Goal

Dry Matter Goal

Horizontal bunker

70-65 percent

30-35 percent

Silo bag

70-60 percent

30-40 percent

Upright silo

65-60 percent

35-40 percent

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