UWEX county agents in cooperation with co-ops, seed industry, farmers and others have measured the rate of corn silage drydown in the field. Two methods are used by county agents to track silage moisture. One method involves harvesting plants from the same area in a field at least weekly. Silage moisture is determined, the rate of silage drydown is calculated, and the date where corn silage is at 65% moisture is projected. The other method consists of "Silage Drydown Days" where samples are randomly brought to a central point and moisture is determined. An average drydown rate of 0.5% is then used to project when a field will be ready for chopping and ensiling.

Environment significantly influences the rate of drydown and start date for silage harvest. The fall of 2000 was more of a "typical" year. Average rate of silage drydown ranged from 0.24 % per day in Outagmie County to 0.68 % per day in Manitowoc County (Table 1). Optimum moisture for a concrete stave silo (65%) was projected for harvest dates between September 13 and 22.

The silage production years of 1998 and 1999 were above normal for heat accumulation and were characterized as rapid drydown years for both grain and silage in numerous counties. Until we measure more environments, we should continue to use an "average" drydown rate of 0.5% per day once the kernel milkline moves in September.

Table 1. Corn silage drydown rate (% moisture per day) for various counties in Wisconsin.
County	1996	1997	1998	1999	2000	2000 Harvest date *
Brown	---	---	---	---	0.56	Sep.16
Chippewa	---	0.43	---	---	---	---
Dodge	---	---	0.67	---	0.60	Sep.15
Fond du Lac	---	---	---	0.76	0.56	Sep.13
Jefferson	---	0.55	0.67	0.97	---	---
Manitowoc	0.36	0.60	0.55	0.78	0.68	Sep. 20
Outagamie	---	---	---	---	0.24	Sep. 22
Shawano	---	---	---	0.61	0.46	Sep. 22
Sheboygan	---	0.78	---	---	---	---
Wakesha	---	0.61	0.87	---	---	---
Washingotn	---	---	---	0.68	---	---
* Projected harvest date for corn silage stored in a concrete stave silo at 65% moisture.