- At an average daily temperature of 15°C, a decrease in moisture of one percentage point may take about five days.
- Once physiological maturity is reached, the grain loses water primarily through evaporation.
- The structure of the ear, husk leaves, and air humidity can significantly speed up or limit the drying of corn.
How does corn release water before harvest?
The process of moisture loss in corn kernels begins while they are still maturing. Initially, the decrease in water content percentage results both from the accumulation of dry matter, mainly starch, and the gradual loss of water from the kernels. However, as they approach physiological maturity, the mechanism of this process changes. The turning point is the appearance of the so-called black layer at the base of the kernel. It marks the end of the transport of assimilates to the grain and the accumulation of dry matter. From that point on, further moisture loss occurs primarily through the physical evaporation of water from the kernels. That is why weather conditions during the final stage of maturation are so important. On warm, dry and windy days, water can be removed relatively quickly. By contrast, high air humidity, precipitation and low temperatures significantly limit the rate of drying.
How many days does it take for corn moisture to drop by 1 percent?
One of the factors affecting the rate of corn maturation is the sum of effective temperatures, known as GDU. In a simplified model, with a base temperature of 10°C, an average daily temperature of 15°C means an increase of about 5 GDU units per day. Under these conditions, it can be assumed as a rough estimate that reducing grain moisture by one percentage point will take about five days. This corresponds to a decrease of about 0,2 percentage points per day. For example, corn with 30 percent moisture could reach about 28 percent after ten days. However, this is an approximate value, not a fixed relationship. GDU is used primarily to assess plant development, while the rate at which water is released also depends on evaporation conditions. In practice, moisture may decrease faster in sunny, dry weather, whereas with cool nights, high air humidity and frequent precipitation, the grain may maintain almost unchanged moisture for many days.
The structure of the cob can speed up or slow down drying.
The variety’s genetics are also important, particularly the structure of the ear and its husk leaves. Varieties whose husk leaves loosen quickly after reaching physiological maturity provide better conditions for moisture loss. If the husk leaves remain green for a long time, cling tightly to the ear and enclose it closely, air exchange is limited. Under such conditions, the drying process may be slower, even when the grain has already reached full maturity. The characteristics of the kernels themselves, their structure and how they are attached to the ear are also important. Therefore, two varieties with similar maturity dates, grown under comparable conditions, may have significantly different moisture levels at harvest. Nitrogen fertilization may also affect this process. Excessive nitrogen supply may contribute to green tissues persisting for longer and delay the drying of husk leaves, which under some conditions may lead tonatural drying of cobs in December.