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Corn test weights in northwest Minnesota lower than desired

Tough growing season. 

In August and September people in northwest Minnesota began to speculate that the later than normal planting dates (in some instances) and mild summer and fall temperatures would have an impact on whether or not the corn crop would reach maturity before a killing frost.  The record-setting rainfall throughout much of the region in September and October brought many cloudy days which also did not help the accumulation of starch during the last bit of the grain fill period.  When it was difficult to find a milk line toward the middle of September, one could anticipate problems.

Corn yield and quality.

In addition to yield, quality is an important consideration when one goes to market or store a corn crop.  One corn quality characteristic is test weight - a measure of bulk density, or the weight of the corn in a bushel, or 37.24 quarts.  Most hand-held moisture meters can typically provide an estimate of test weight.

The USDA’s Grain Inspection, Packers and Stockyards Administration (GIPSA) grades corn by the maximum limits of damaged kernels, broken corn and foreign material and minimum test weight. Corn that is graded U.S. number 1 has a minimum test weight of 56 pounds per bushel, while corn graded U.S. number 2 through 5 has lower minimum test weights and higher maximum limits of damaged corn, broken corn and foreign materials (Table 1, USDA-GIPSA, 1996).

Table 1. Corn grade test weight requirements (source: USDA-GIPSA)*

Minimum test weight per bushel
U.S. No. 1
U.S. No. 2
U.S. No. 3
U.S. No. 4
U.S. No. 5
* For additional information about maximum limits of damaged kernels, broken corn and foreign material, consult GIPSA standards section 810.404 (Grades and Grade requirements).

NWROC corn plot yields.

The technical crew at the UMN Northwest Research and Outreach Center (NWROC) in Crookston recently used a carefully calibrated small-plot combine to harvest my corn plots. Unlike most farmers in the region that are waiting for the crop to dry a bit more before harvest, the technical crew quickly harvested these research plots as their smaller-sized equipment gets easily bogged down in snow.  The crew then provides a report of the weights, moisture contentss, test weights and moisture-standardized yields for each plot. 

While moisture levels were still above 25 percent in many plots, moisture-adjusted yields ranged between 166 and 242 bushels per acre. In addition to the high moisture levels which will increase production costs to remove, test weights were poor, ranging from 48.6 to 52.8 pounds per bushel.  Twenty percent of the plots would have been graded U.S. number 3, seventy two percent number 4 and eight percent U.S. number 5 corn (Figure 1). 
Figure 1. Test weights (in pounds per bushel) of corn plots in a research study at the Northwest Research & Outreach Center in Crookston, and the minimum test weight of different grades of corn according to USDA-GIPSA.

When I called around to do an informal survey of elevators in the region to ask about whether they were accepting corn, I received a number of different answers, including: 1) we are currently loading a train with soybeans and can only accept corn with 15% or less moisture, 2) we are currently loading a train with wheat and can’t accept corn right now, check back tomorrow, 3) we are accepting corn.  For those that were accepting corn, discounts due to low test weights ranged between 30 and 45 cents per bushel.  When one also factors in drying costs total discounts could be greater than $1.15 per bushel.  One of the elevator managers candidly shared that the uniformly poor quality corn has meant that he is simply unable to blend this problem away. 

Why is low test weight corn worth less?

Same volume, lower weight. On a per bushel basis, U.S. number 1 and number 5 graded corn take up the same space – 1000 bushels of number 1 corn has the same volume as number 5 corn.  While grain yields are typically expressed as a volume (bushel) for a given area (acre) when one delivers corn, trucks are weighed before and after delivering the crop and farmers are paid according to weight.  So when one delivers 1000 bushels of number 1 corn with a test weight of 56 lb/bu, they will get paid for delivering 56,000 pounds of corn.  However, when one delivers 1000 bushels of number 5 corn with a test weight of 47 lb/bu they will get paid for delivering 47,000 pounds of corn, which is like delivering 839 pounds of 56 lb/bu test weight corn (47,000 divided by 56).  

Brittle kernels. Lower test weight corn kernels tend to be more brittle and less able withstand handling, resulting in increased breakage and fine materials. Fine materials can decrease efficiency of air movement during storage (Hurburgh, 2019) and broken kernels can be more easily colonized by fungi. Neither fine materials nor kernel breakage are positive developments for long-term storage. 

Feed efficiency. Much of the dent corn grown in the U.S. is used for animal feed. According to University of Nebraska-Lincoln Extension educator Todd Whitney, higher test weight corn is more nutrient dense as overall there tends to be a lower proportion of bran and hull and a greater proportion of starch-rich endosperm (Whitney, 2017).  When compared to high test weight corn, livestock producers would need to store, handle and feed larger quantities of low test-weight corn.


Angie Peltier, UMN Extension crops educator

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