Grain moisture content continually decreases as the kernel develops and matures. The rate of grain moisture loss during post-maturity drydown and the resulting grain moisture content at harvest is obviously of great interest to growers, the seed industry, and grain buyers.
Loss of grain moisture occurs partially through the plant (cob and ear shank), the husk leaves, and the exposed end of the ear. Certain hybrid characteristics (Table 1) interact to influence grain moisture loss rates. The relative importance of each trait varies throughout the field drydown period, as well as from year to year.
Table 1. Hybrid characteristics desirable for rapid grain moisture loss in the field.
|Hybrid characteristic||More rapid grain moisture loss occurs with...|
|Husk leaf number||Fewer number of husk leaves.|
|Husk leaf thickness||Thinner husk leaves.|
|Husk leaf senescence||The sooner the husk leaves senesce (die).|
|Husk coverage of the ear||The less the husk covers the tip of the ear.|
|Husk tightness||The looser the husk covers the ear.|
|Ear declination||The sooner the ears drop from an upright to a downward position.|
|Cob diameter||The narrower the cob diameter.|
|Kernel pericarp thickness||The thinner the pericarp.|
Severe stress during grain fill can cause premature 'shutdown' of the grain maturation process, resulting in premature development of the kernel black layer. Examples of such stress include extensive loss of green leaf tissue from disease, drought or hail damage, extensive damage to stalks and ear shanks from European corn borer (ECB) tunneling, and sub-optimal cold temperatures (see accompanying article on the effects of cool night temperatures).
Grain that ceases grain fill prematurely will also begin its post-maturity field drydown period earlier in the late summer or early fall. Rates of grain moisture loss will be greater because of the relatively warmer temperatures and the field will reach a harvestable moisture level sooner than an unstressed field. By the same token, variable stress throughout a field will often result in variable grain moisture levels in the grain you harvest from that field.
It is no surprise that corn that matures early in the fall in warmer weather will dry faster per day than corn that matures later on in cooler weather. The rate of grain moisture loss in early September can range as high as one moisture percentage point per day and will often average greater than 3/4 moisture percentage point per day.
By late September and early October, typical rates of grain moisture loss decrease as temperatures continue their normal seasonal decline. Grain moisture loss during this period may range from 1/2 to 3/4 moisture percentage point per day.
By late October and early November, don't expect grain moisture loss rates to exceed 1/4 moisture percentage point per day. In the late harvest season of 1992, rates of grain moisture loss at the Purdue Agronomy Research Center near West Lafayette were about 0.16 moisture percentage point per day during mid- to late October and nearly non-existent in November.
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