Minnesota Crop News > 2001-2008 Archives
Test Weight Changes During Drying
Hicks, Department of Agronomy and Plant Genetics, University of Minnesota
Some of this year’s corn crop will
not reach normal maturity before the next killing freeze.
As a result, maximum yield potential and normal test weights
will not occur. Test weights in the low 50’s(lb/bu)
may be common in some areas the state, especially in the
northern half of MN. Test weight can increase with artificial
drying if the drying temperature is maintained below 180°F.
Research at the University of Illinois and Iowa State
University showed mature corn increased
in test weight when dried to 15% kernel moisture (KM).
The size of the increase depended upon the hybrid, mechanical
condition of the grain, and drying temperature. Greatest
increases in test weight occurred with good quality corn
(less than 10% cracked kernels) dried at temperatures less
than 180°F. The summary of that research showed that
test weight increases could be expected as shown in Table
1 when drying mature grain to 15% KM.
Table 1. Increase in test weight
during drying for mature corn harested between 18 and
28% kernel moisture content.
Source: University of Illinois and Iowa State University
We conducted a study to measure the effect of stage of
kernel maturity and drying temperature on the change in
test weight during drying. Ear samples were harvested from
normally growing plants beginning August 27 and continued
at approximately 10-day intervals until October 13. Grain
was shelled and wet test weight and KM were measured. Kernel
samples were split and put into either a high (120°F)
or low temperature (80°F) oven for drying. Samples were
removed from the oven every 1 to 4 days to measure test
weight and KM. Samples were replaced in the oven to continue
drying and subsequent measurements of test weight and KM
Wet test weight and test weights after drying to 15.5%
moisture are shown in Figure 1 for corn harvested on six
calendar dates. Moisture contents given across the bottom
of the graph correspond to the six harvest dates; kernel
development for the six harvest dates were soft dough,
early dent, well dented, nearly mature, mature, and mature.
The three bars in the figure for each kernel moisture level
shows the initial wet test weight (bar 1) when the grain
was harvested and the test weight after drying to 15.5%
KM with 80°F temperature (bar 2) or with 120°F (bar
Wet test weight for corn in the soft dough stage at 52.5%
KM was 52 lb/bu, but dropped to less than 46 when dried
to 15.5% KM. When corn was in the soft dough and early
dent stages for the first two harvest dates, test weight
did not increase when drying to 15.5% KM.
After grain had reached the well-dented stage, test weight
increased about 4 lb/bu when dried to 15.5% KM with either
drying temperature. Moisture content was 17.5% for the
last harvest date and there was no change in test weight
during drying because the change had already occurred as
kernels dried in the field.
These drying temperatures were below 180°F recommended
by Illinois and Iowa to achieve the increase in test weight
during artificial drying. However, the test weight increase
when drying kernels in the well-dented stage was greater
using 80° than when drying with 120°F (third group of
3 bars in Figure 1). Temperature had no effect on the test
weight increase during drying for nearly mature and mature
kernels (last 3 groups of bars in figure 1).
For corn that is not mature this year when frozen, the
test weight will be lower than it would have been with
normal growing to maturity, even after careful drying.
But some increase in test weight should occur during drying
for corn that has progressed in maturity to or past the
well-dented stage. Dry test weight should be 54 or higher,
particularly if the drying temperature is less than 180°F. For other corn that has not well-dented when frozen,
the dry test weight is not likely to reach 54.
Figure 1. Wet and dry test weights for grain
harvested at soft dough through mature kernel stages
and dried to 15.5% kernel moisture with temperatures
of 80° or 120°F.