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Iowa | From Purdue-- shows relationship between test weight and Grain moisture
Tommy
Common Causes of Low Test Weight Corn
So far this 2009 harvest season in Indiana, there are more reports of low test weight corn grain than good or above average test weights. There are primarily six factors that account for most of the low test weight grain in 2009 and four share a common overarching effect.
First and foremost, growers should understand that test weight and grain moisture are inversely related. The higher the grain moisture, the lower the test weight. As grain dries in the field or in the dryer, test weight naturally increases as long as kernel integrity remains intact. Test weight increases as grain dries partly because kernel volume tends to shrink with drying and so more kernels pack into a volume bushel and partly because drier grain is slicker which tends to encourage kernels to pack more tightly in a volume bushel.
Therefore in a year like 2009 with many of the initial harvest reports of grain moisture ranging from 25 to 30% instead of the usual starting moisture levels of about 20 to 23%, it should not be surprising that test weights are lower than expected. Hellevang (1995) offered a simple formula for estimating the increase in test weight with grain drying. In its simplest form, the equation is (A/B) x C; where A = 100 - dry moisture content, B = 100 - wet moisture content, and C = test weight at wet moisture content. The author does not say, but I suspect this simple formula is most applicable within a "normal" range of harvest moistures; up to moistures in the mid- to high 20's.
Example: Dry moisture = 15%, Wet moisture = 25%, Test weight at 25% = 52 lbs/bu.
Test weight at 15% moisture = ((100 - 15) / (100 - 25)) x 52 = (85/75) x 52 = 58.9 lbs/bu
Edited by Tommy 10/30/2009 09:51
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test weight in corn-example from Purdue
