Corn Verification Crop Progress Update

Erick Larson, State Extension Specialist - Grain Crops
By Erick Larson, State Extension Specialist - Grain Crops July 22, 2011 15:00

Our cooperator’s irrigated Corn Verification fields planted from March 19-23 near or slightly south of Highway 82 in the Delta will reach physiological maturity (black layer) July 23-28.  Soil moisture was not sufficient to sustain these fields until maturity, so they were irrigated one last time this week (except for one field where the water supply has dried up).   Fields planted  further north, or of course later, should mature later.

Climatic records show this season’s growing degree day (GDD50) accumulation at Stoneville for a March 20 corn planting date are currently about four days ahead of normal.  However, this is at least one day behind schedule compared to last year.

Corn grain normally dries about 0.6% per day in Mississippi after it reaches physiological maturity or black layer (when moisture is around 30%) down to 15% moisture depending upon environmental conditions. Given “normal” hot, dry late July-August weather, corn should dry faster than 0.6% per day at high moisture and slow as grain moisture drop into the mid-teens. However, when rainfall persists, along with cloudy days, high humidity and low temperatures, grain drydown will slow considerably or be suspended, much like in 2008 and 2009.

Corn grain drying rate after physiological maturity is primarily dependent upon environmental conditions. The “black layer” is an abscission layer that effectively cuts off moisture and nutrient transfer between the plant and the grain. Thus, using a harvest aid to kill green corn leaf tissue or weeds will have little or no significant effect on grain drydown rate, since there is no longer any active moisture transfer between plant and grain, and husks senescence (naturally die) near physiological maturity. Some plant characteristics, including husk coverage/thickness/tightness and ear orientation may influence drying rate, but these characteristics generally are less important than weather conditions. In summary, there is little you can do now to effect corn grain drying rate in the field. Hopefully, this year we will be blessed with good corn harvest weather, but still receive ample rainfall for other later-maturing crops.

Root lodging can be a serious hindrance to harvest efficiency because the entire stalk falls down. Now is the time to evaluate hybrids for differences to this issue. Photo is from a previous year.

One issue that developed recently in two verification fields was some minor root lodging caused by wind associated with storms last week.  In each case the root lodging was scattered and generally occurred in intermittent stalks (less than 5%), rather than large areas.  This specific type of lodging often causes stalks to severely lean or completely fall, and may dislodge part of the root system from the soil.  Root lodging may be substantially influenced by hybrid genetics (as in this case), so closely evaluate hybrids now for potential differences.  Root lodging often occurs as plants approach physiological maturity (when plant is still green), because the mass of the plant is more than any other time during the season (maximum ear weight and the stalk is full of water).  This type of lodging substantially hinders harvest efficiency, because stalks lay nearly flat on the ground and are partially uprooted from the soil.  Thus, stalks are difficult to pick up and flow poorly through the combine header.

Percent of normal precipitation for a 14 day period ending July 22, 2011.

The primary issue for our dryland verification fields continues to be drought stress.  Unlike most of the Delta region, frequent April rainfall delayed corn planting in northeast Mississippi well into May.  Although one of our cooperator’s March-planted dryland verification fields is now reaching physiological maturity, May-planted fields range from silk to dough stage and are extremely dependent upon rainfall to supply moisture for another month or more.  Ears have generally successfully pollinated in dryland verification fields. However, drought stress has been considerable and certainly will reduce productivity, especially if it persists.

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Erick Larson, State Extension Specialist - Grain Crops
By Erick Larson, State Extension Specialist - Grain Crops July 22, 2011 15:00
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