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Grain moisture content should start to be monitored soon after physiological maturity (black layer). Shoot for a harvest moisture content level that balances harvest losses and grain drying costs. A plan to take advantage of a rapid drydown and allow everything to field dry could be costly. Harvesting at lower moistures can increase mechanical losses due to ear drop, stalk lodging, and kernel shattering. Consider beginning harvest when corn grain moisture content is a little above 25% so that harvesting can be finished before corn dries completely in the field.1
With high temperatures, it is extremely easy to underestimate the rate that grain dries. Grain that matures in late August can have an average daily drydown rate of approximately 0.8 percentage point per day compared to 0.4 percentage point per day for grain nearing maturity in mid to late September.2
To test for grain moisture content, randomly select 10 ears, remove several rows of corn kernels from the full length of the ear, and mix the kernels thoroughly. Use a calibrated moisture meter to determine the moisture content. At least three moisture samples should be taken to acquire an average moisture content.
Some research information suggests that yield may “disappear” after physiological maturity due to respiring grain in the field (“phantom” yield loss). The question then becomes, is it better to harvest higher moisture content corn and pay the drying cost to avoid a potential yield loss or leave corn standing in the field to dry down naturally? Corn respiration rates are greatest when grain moisture is near 50 percent and decreases as grain dries. Higher temperatures and mechanical damage can increase kernel dry matter loss. Due to respiration and under favorable fall weather, good quality corn grain may take 25 to 50 days for a one percent loss in dry matter.3 This estimate does not support the one percent dry matter loss for each percentage point of grain moisture content lost after black layer.
Corn dry matter may decrease by as much as 0.6 to 1.6 percent for each percentage point lost in grain moisture content after black layer.2 Historical data from Purdue University in Indiana, identified the decrease in kernel dry weight during field drydown using three corn products. Harvested grain kernel dry matter was measured twice during the week from the time the kernels were about 40 percent moisture content and continued until the moisture contents were less than 20 percent. The average percentage loss in kernel dry matter ranged from 0.9 to 1.3 percent for the three corn products tested. Kernel dry matter loss, averaged across corn products for each year, ranged from zero to 1.2 percent per point of kernel moisture lost (Table 1).
In a two-year study conducted by University of Nebraska researchers in south-central Nebraska, it was found that corn grain dry matter was stable after black layer across multiple corn products. Average grain yields for six corn products were similar over the eight harvest dates each year. In contrast to the Purdue University study, machine harvest losses were accounted for and incorporated into the yield data (Table 2). Kernel weights differed between corn products but within each product, kernel weight was constant. From these findings, researchers concluded that there was no evidence of kernel dry matter loss after black layer.4
The University of Nebraska researchers suggested that the differences between their study and the Purdue University findings were due to different methods of determining grain moisture content and that harvest losses were not accounted for in the final Purdue University yield data.3 Researchers at Purdue University used and electronic moisture meter to estimate grain moisture content, which can be less accurate compared to an oven-dry method when moisture contents are above 25 percent.3 Ultimately, both studies reinforced the guideline that optimum grain moisture content for harvest is around 25 percent.
Existing and potential stalk and root lodging, disease pressure, and moisture content can affect harvest order. Stalk cannibalization and physiological stalk lodging can be due to nitrogen loss from excessive early season rainfall. Anthracnose top die-back and stalk rot can be prevalent in certain years. With excessive cannibalization and abundant stalk rots, fields need to be monitored closely to develop a harvest schedule that can help minimize lodging and harvest loss.
The pinch and push tests are two methods to determine stalk integrity. The pinch test is conducted by squeezing the second or third internode above the ground. If it collapses, stalk quality is compromised. The push test is performed by pushing a corn stalk to approximately a 45 degree angle. If it breaks, stalk quality has been reduced. Conduct either test on 10 plants in a row and at several locations in the field. If more than 10% of the stalks tested show poor stalk quality, or lodge at the root, the field should be slated for early harvest.
In addition to harvesting at an optimum grain moisture content, achieving proper combine settings can help increase combine efficiency, maximize grain quality, and minimize field losses. Always follow the manufacturer’s equipment setting recommendations. Listed below are a few combine preparation tips:5
Fields with considerable lodging should be harvested early to help minimize the risk of increased lodging and ear rots. Harvesting tips to help protect yield potential in fields with lodging include:
Stored corn should be checked frequently. Bins should be inspected every one to two weeks in the fall and spring, and once every two to four weeks after conditions in the bin have stabilized during the winter months. Preventative practices can be implemented to help protect corn from spoilage during storage: