Pawel Wiatrak and James R. Frederick
Corn harvest date should be determined by crop maturity. Most kernels accumulate dry
matter until moisture decreases to about 30-35% percent. Ideally, corn should be harvested between 15 and 18% moisture do reduce drying costs. However, in order to reduce mechanical damage during harvest, it is recommended to harvest corn at about 22% (for large corn acreage, corn harvest should begin at 25%).
Higher kernel damage usually occurs below and above this moisture content. High moisture of 30% and above would also result in poor kernel separation from the cob. Harvesting at 15% and lower results in high levels of cracked and broken kernels. Preharvest losses at low moisture content will depend on insect damage, lodging, ear drop, and reductions to kernel weight. It is recommended to start harvesting fields with potential losses.
If corn has been grown under stress conditions (moisture, insect stress, etc.) it may be contaminated by aflatoxins. Aflatoxin may also increase due to delayed harvest. Therefore, harvest and drying of aflatoxin contaminated corn is recommended as early as possible to reduce aflatoxin increases. Generally, corn should be dried to 13% moisture or less if it is to be stored for several months.
During harvest, combine cylinder speed and cylinder-concave clearance should be properly adjusted to minimize kernel damage and loss. Damage increases with increasing cylinder speed. The adjustments should be made after harvesting the small area. Also, count the kernels left on the ground. The loss of two kernels per square foot equals approximately the loss of one bushel of corn per acre, and therefore a loss in profit.
High combine speeds can result in significant yield losses. When the ideal moisture is obtained, harvest should begin as soon as possible to avoid lodging problems. Small increases in lodging will result in substantial decreases in grain yield. Losses due to lodging can be minimized by slowing down the speed of combine and harvesting as soon as the grain moisture is optimum for harvest.
In some situations (insurance purposes, calculate storage needs or loss due to lodging, etc.) there is a need to estimate the grain yield of corn prior to harvest. The most widely method to estimate corn yield is called the Yield Component Method which was developed at the University of Illinois.