Sunday, August 15, 2010

Corn Maturity Moving Along

This is a shot of ear 38M58 taken on August 14 which is 34 days after this hybrid began to flower on July 10.  It took about 5 days for pollination to occur after the first silks emerged, so this corn was done pollinating on July 15-16.  You can see it is now in the dent stage of development.  
After pollination, corn advances through 5 stages of 12 days each, or a total of 60 days, to reach physiological maturity.

1. Milky embryo or blister stage      
2. Young sweet corn stage
3. Beginning dent stage
4. Half milk line stage
5. Hard dent stage

The above hybrids have a spread in maturity as follows, with corresponding pollination dates.
38M58 - 2850 CHU - pollinated July 15
P9623HR - 2850 CHU - pollinated July 15
P9855HR - 2900 CHU - pollinated July 19
P0118HR - 3050 CHU - pollinated July 22
P0125HR - 3050 CHU - pollinated July 22

A hybrid that silks on July 10 will reach physiological maturity, which is defined as 33-34% grain moisture, on or about September 15.  Physiological maturity occurs when a layer of abscission cells form between the kernels and the cob.  The abscission layer, commonly known as black layer, stops the movement of water and nutrients from the ear to the kernel.  All moisture trapped in the kernel now has to migrate out through the skin of the kernel. 
Heat has the greatest effect on drydown.  It has been proven that it takes about 35 CHU to drop grain moisture 1 percentage point.  During September in the London area we receive on average 19 CHU's per day, based on long term temperature records. 
If we have 15 days left in September, we can expect to accumulate 285 CHU's (15 x 19).  Grain that is 35% moisture on September 15 should then lose 8 points of moisture (285 / 35) and be approximately 27% by the end of the month.  If heat continues to accumulate at an above average rate, it is possble that corn will be 25% moisture on September 30.
After corn reaches 25% it takes more heat, 50 CHU's vs 35 CHU's, to take moisture from the kernel.  In October we receive about 6 CHU's per day.  Therefore we would expect to lose 3-4 points of moisture (180 / 50) by the end of the month.  Combining corn that is in the low 20's in October is always a pleasure.
Remember these are averages and local conditions can create exceptions. 

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