Many fields in Wisconsin had uneven crop development during the 2003 growing season. Beginning about August 1, knoll areas of many fields began to roll leaves early in the morning. As the drought continued more and more corn plants further off the knoll began to exhibit early morning leaf rolling and faster kernel development.

We were interested in the forage moisture differences of corn in knoll and swale areas of the field. In one field at Arlington, we measured forage moisture of corn plants growing approximately 50 feet apart. On every sample date we went back to the same areas and harvested plants for tracking silage drydown, as well as changes in yield and quality. Figure 1 shows the results of forage moisture changes. Corn growing on the knoll was "browner" than corn growing in the swale, and by September 5 corn on the knoll was brown over the entire height of the plant.

Significant rain events occurred on August 28 and for three days around September 13. On all sample dates, corn forage moisture of the knoll was 7 to 20% lower than the swale. After the rain event of September 13, forage moisture of corn growing on the knoll increased from 40% to 55%, but three days later quickly fell back to 40%. Corn growing in the swale rehydrated from 60% to 63%.

These observations were somewhat surprising. We have much to learn yet about how environment interacts with corn forage drydown rate. In the past we have generally observed a linear drydown pattern for corn during September at the rate of 0.5% per day (range = 0.4 to 0.7% per day depending upon year). Significant rainfall, in this case 3.5 inches, can significantly increase forage moisture. Whether we can use this observation for corn silage management remains to be seen since these fields were very wet and allowing heavy equipment into the fields could cause more problems than benefits with increased potential for compaction and soil structure loss.

Figure 1. Forage moisture of corn growing on a knoll and a swale at Arlington during 2003. Each value is the mean of three sampling sites.