The temptation to harvest corn for silage on a schedule with most normal growing years may be great. However, if harvested prematurely, yield will be lower and quality will be poor. Unlike other grasses grown for hay or haylage, where high quality forage is achieved by harvesting before mature seedheads develop, with corn a fully developed ear with complete grain fill is necessary for maximum yield. This occurs at physiological maturity. Greater feed value may be achieved by harvesting slighlty before this at the mid to late dough stage of grain development. Sid Lyford suggests aiming for maximum starch and minimum hardness to reduce grain by-pass during digestion.
Physiological maturity is achieved when kernels cease accumulating dry matter. At this time, the plant may be 50% stover and 50% ears on a dry matter basis. However, the stover from such a plant would supply only about 33% of the energy while the ears would supply approximately 67% of the energy. Harvesting too early will lower dry matter yield and especially energy yield with poorly filled kernels.
A guide to identifying physiological maturity is to look for "black layer" formation in corn kernels. When kernel dry matter accumulation is complete several layers of cells near the tips of kernels in most hybrids turn black forming the "black layer". At physiological maturity the kernels contain 30 to 35% moisture, the ear corn will contain 40 to 65% moisture, and the whole plant will contain 62 to 68% moisture or 32 to 38% dry matter. Under favorable moisture and fertility conditions, most of the leaves will be green and the grain will be in the full dent stage. This is the ideal stage for ensiling. Also, corn harvested with over 70% moisture will seep, especially when stored in upright silos. The seepage carries with it soluble sugars, proteins, and organic acids. Cattle also eat less when fed high moisture silage. Similarly, if the crop is harvested too late, dry matter yield is reduced because of leaf loss, dropped ears, and stalk breakage. Additionally, proper packing is difficult and may result in serious heat damage and marked depression in digestibility of the protein of the corn crop.
The dry matter of silage (corn and haycrop) fed on most dairy farms is usually in the range of 25 to 40%. This contrasts with hay or grain mixtures, which for safe storage have moisture contents as low as 10 to 13%, that is dry matter contents of 87 to 90%. In calculating balanced rations, animal nutritionists point out that the moisture content of the various components needs to be known or estimated. Research data indicate if the moisture content of a mix for a group of high producing cows becomes too high, then total dry matter intake of these cows will drop.
Harvesting corn on time so that silage is neither too wet or too dry improves silage preservation and animal intake and is another reason for allowing your corn crop to reach its maximum potential.
Stephen J. Herbert
Dept. of Plant and Soil Sciences
University of Massachusetts Amherst
Crops, Dairy, Livestock News. Vol. 2:2, Summer 1997
Last updated: 3/15/05.