Grain corn in Manitoba is maturing quickly, and as seen on Twitter, some of the earliest planted fields have reached physiological maturity. Normal plant processes and weather conditions are the major influences on grain dry down, although hybrid characteristics can also play a role. As corn harvest approaches, a quick review of the facts concerning grain drydown might be helpful.
Grain drydown can be separated into two stages: the grain fill period and after physiological maturity.
Drydown During Grain Fill. The grain fill stages (R1 to R5) begins at flowering and is completed at physiological maturity. Grain filling is characterized by the rapid accumulation of dry matter in the kernel and the rapid movement of water out of the kernel. Decreases in kernel moisture occur from a combination of actual water loss (evaporation) from the kernel surface and the accumulation of dry matter. The corn plant uses “internal plumbing” to move water out of the kernel since water movement out of the kernel is regulated by how much dry matter is being forced into the kernel. The corn plant is much more efficient in removing water from the kernel using its “internal plumbing” instead of physical evaporation through the kernel surface.
Drydown After Physiological Maturity. Physiological maturity (R6) occurs when kernel moisture is at approximately 30 to 32% (but can vary). At this stage of growth, a layer of cells at the base of the kernel dies and turns black (hence black layer), the “internal plumbing” is therefore disconnected, and a barrier is formed between the kernel and the corn plant. For this reason, post-maturity grain moisture loss occurs primarily by evaporative loss from the kernel itself. Research many years ago established that post-maturity moisture loss through the kernel connective tissues (placental tissues) back to the cob is essentially non-existent.
Role of Weather. As moisture loss after maturity is due to physical evaporation, field drying of mature corn grain is influenced primarily by weather factors, especially temperature and humidity. In simple terms, warmer temperatures and lower humidity encourage rapid field drying of corn grain.
Because moisture loss is greatest just after physiological maturity, both because the weather is usually warmer and because wet kernels lose water more easily, it stands to reason that a corn crop that matures earlier in the season will dry down faster than a crop that matures later in the season. However, it is important to keep in mind that grain moisture loss for any particular day may be quite high or low depending on the exact temperature, humidity, sunshine, or rain conditions that day. It is not unheard of for grain moisture to decline more than one percentage point per day for a period of days when conditions are warm, sunny and dry. By the same token, there may be zero dry down on cool, rainy days.
Role of Hybrid Characteristics. A number of hybrid characteristics can influence the rate of dry down, but to a lesser degree than weather. However, when weather conditions are not favorable for rapid grain dry down, hybrid characteristics that influence the rate of grain drying become more important. The relative importance of each trait varies throughout the duration of the field dry down process and, as mentioned earlier, is most influential when weather conditions are not conducive for rapid grain drying.
- Husk Leaf Number. The fewer the number of husk leaves, the more rapid the grain moisture loss.
- Husk Leaf Thickness. The thinner the husk leaves, the more rapid the grain moisture loss.
- Husk Leaf Senescence. The sooner the husk leaves senesce (die), the more rapid the grain moisture loss.
- Husk Coverage of the Ear. The less the husk covers the tip of the ear, the more rapid the grain moisture loss.
- Husk Tightness. The looser the husk covers the ear, the more rapid the grain moisture loss.
- Ear Declination. The sooner the ears drop from an upright position to a downward position, the more rapid the grain moisture loss.
- Cob Diameter. The narrower the cob diameter, the more rapid the grain moisture loss.
- Kernel Type. Flint-dent kernel types tend to dry down slower in comparison to dent kernel types due to the harder nature of the kernel.
Originally Posted on Crop Chatter in September 2016
Last Revised September 2017