This NebGuide disputes previous reports that corn yields are reduced after black layer if harvest is delayed. An October 1995 article in a national farm publication reported that corn dry matter decreased 1 percent for every percent loss in rain moisture as corn dried in the field after black layer (physiological maturity). The dry matter loss reportedly was hybrid specific and possibly due to seed respiration. This observation was based on research conducted at Purdue University with three hybrids over four years. All hybrids tested had significant dry matter losses in three of the four years. A report of similar observations from farmers and agronomists appeared in 1984 in a regional farm magazine. Many farmers have also documented yield losses associated with delayed harvest. If large dry matter losses occur during field dry down, it may be more cost effective to dry grain with artificial heat.. Several researchers have investigated kernel weight and/or yields after black layer. In most of the studies no changes in kernel dry weight were observed following black layer; however, in one report, four of 18 hybrids and five of 42 hybrids studied had changes in kernel dry matter as corn dried from 35 percent to about 15 percent grain moisture. Of the hybrids with dry matter changes after black layer, some had increased dry matter and some had decreased dry matter. These dry matter changes however, were not consistent over years.. Seed respiration is cited as a possible cause for the reported large dry matter losses following black layer. Respiration rates are greatest when grain moisture is near 50 percent and decreases to a minimal level as grain dries to 15.5 percent. These dry matter losses increase with greater temperatures and with greater mechanical damage to kernels. But, with good kernel quality and typical fall temperatures in the corn belt (average daily temperatures ranging between 50°F and 65°F), it would take an estimated 25 to 50 days for 1 percent dry matter loss to occur from respiration. This is far less than the 1 percent dry matter loss reported for every percent moisture loss after black layer
