Limitations to Kernel
  Milk-line for Predicting
  Silage Moisture
 

Over the past five to six years agronomists and animal scientists have recommended that the kernel milk-line be used to determine when to begin corn silage harvest. Research from the 1980's indicated that the optimum 60 to 70% whole plant harvest moisture for silage fermentation corresponded closely to when the kernel milk-line had moved ½ to 3/4 the distance from kernel crown to tip (point of attachment to cob).

Finding the milk-line

Finding the kernel milk-line is not difficult. Break a corn ear in half and look at the top half (the one farthest from the stalk with the "pointed" end). After dent stage begins, a line can be seen on the smooth side of the kernels. It marks the boundary between the solid and liquid parts of the immature kernel. The progression of this line from crown to base can easily be followed. When the milk-line reaches the kernel base, black layer formation or maximum kernel dry matter accumulation is obtained.

Milk-line limitations

Although corn researchers in several states have confirmed the utility and accuracy of using the kernel milk-line method to gauge optimum harvest moisture, there is also evidence to show that milk-line and whole plant moisture variations do exist between hybrids and environments. For example, a summary of Wisconsin data from all experiments where milk-line and whole plant moisture were measured shows a range of 52% to 72% moisture at half milk-line across hybrids and years even though the average was an optimum 63 percent (Figure 1). The variation exists largely because of extreme environmental conditions and differences in specific hybrids related to their ability to lose whole plant moisture at the same rate as grain maturity. The stover "stay green" characteristic likely plays a role in this relationship.

What can be done?

If milk-line is used as sole means of estimating whole plant moisture, it will be most accurate if based on the historic performance of the individual hybrid. This information is often available from the seed company or within the silage trial results published by the University of Wisconsin. Joe Lauer, UW Extension Corn Specialist, now recommends milk-line be used as a "trigger" to begin monitoring whole plant moisture. Although it takes more time and effort, using a microwave oven or Koster Tester for verification is the best approach to obtain accurate whole plant moisture readings.