Reliability of the kernel milkline method for timing corn silage harvest in Ohio

The position of the kernel milkline (ML) has been recommended as a reliable guide for determining the optimal time to harvest corn (Zea mays L.) for silage. This method has not been tested adequately in the central and eastern Corn Belt, and the effect of planting date on variation in whole plant dry matter (DM) content at different ML stages is unknown. The objective of this research was to determine the variation in whole plant DM content at different kernel ML stages of corn grown in Ohio. Three hybrids representing early, mid, and full season maturities for central Ohio were planted on or about 1 May, 21 May, and 10 June 1992 and 1993. Kernel ML stage and whole plant DM content were determined every 3 to 7 d beginning at full dent (FD) stage until ML disappearance. Kernel ML stage and whole plant DM content were positively correlated (r = 0.89). On average, the kernel ML would have been an excellent indicator of when to harvest corn for silage; however, we found considerable variation in plant DM content within a given ML stage for individual sampling dates from all hybrids and environments. Variation in DM content was present regardless of year, planting date, or hybrid. Although corn was more likely to be at an ensilable DM content at certain stages than others, the variation in plant DM content within a stage was sufficient to raise concern over the reliability of the kernel ML method for determining when to harvest a particular field for silage in Ohio. Gravimetric determinations of plant DM content should be used to confirm when corn is at the optimal DM content for ensiling. Corn silage growers in Ohio should begin making gravimetric determinations of plant DM content at FD for conventional tower or bunker silos, and 1/4 ML for sealed (oxygen-limited) tower silos.