AgriGold

Dry Down & Test Weight

by Kevin Gale, CCA, October 20, 2009

The 2009 corn crop continues to lag 3-4 weeks behind normal with some areas still not mature. Many corn fields
are ranging from 25%-35% + moisture and trying to dry down despite the recent stretch of rainy weather. Unfortunately the forecast for the next seven days does not show much improvement with rain events and potential killing freeze next week (October 12). Potentially 20% of the US corn crop may not be mature by this date. Many growers are hopeful this crop will dry down in the field to reduce drying costs. However, dry down dates of corn drops quickly as we progress through October. Additionally, stalk quality and late season harvestability will need to be monitored closely due to stalk rot & lodging potential. In this edition of “Scouting Your Corn Acres” we will discuss dry down potential this fall and characteristics that affect dry down of corn hybrids. Test weight and storage of lower quality grain will also be covered.

A cool, long growing season typically results in high yields and this year is no different. The USDA suggests a record of 162+ bushel national average for the 2009 corn crop. High yields however will most likely come with higher grain moisture and reduced test weights in the northern half of Illinois. As we begin to think about harvest, dry down of this slow maturing crop is the first thought that comes to mind. Once corn reaches black layer, several factors affect overall speed of dry down. Obviously weather is important, especially temperature and humidity or rainfall. Warm, dry conditions accelerates drying and cool, wet conditions slows drying. In addition, late planted, full season products in general tend to dry more slowly. When considering heat units, 30 GDU’s will remove 1 point of moisture from 32% (black layer) to 25%. 45 GDU’s will be required to dry corn 1 point from 25% down to 20%. With temperatures forecasted in the 50’s & low 60’s this week, we may gain enough heat units to dry corn ~1-2%. Lets hope for an early, extended Indian Summer!

Hybrid characteristics affect on field dry down. Hybrids vary in how they dry down in the field after maturity. During good weather conditions, grain dry down rates are relatively similar between hybrids. However, when weather conditions are not conducive for rapid dry down, hybrid characteristics become important to determine rate of grain drying. These would include kernel pericarp thickness, size and density of kernel, husk leaf number and thickness, husk coverage of the ear, tightness of husk and time of ear drop after maturity.

Test weight may become a topic of discussion as we harvest a wetter than normal crop. Test weight is
expressed as pounds per bushel, with 54 being market standard. Kernel size, shape and density all affect test
weight. High test weights result when grain fills completely and has a higher percentage of hard endosperm and
protein. Low test weight implies grain may not have matured entirely or was subject to some stress during the
growing season.

Factors That Reduce Test Weight

1. Planting later than normal.
2. Planting early hybrids for a given area.
3. Low Nitrogen availability (Low rates applied, denitrification, Leaching).
4. Wet &/or cool growing conditions (increased starch / decreased protein in kernel).
5. High plant populations.
6. Leaf disease reducing photosynthesis (Eyespot, GLS, Northern Corn Leaf Blight, Rust, etc.).
7. Cloudy days and foggy conditions.
8. Hail damage.
9. Premature death due to disease (Top Dieback, etc.).
   
10. Any stress to push reproductive stages along, including the only dry spell experienced this year during grain fill when plants were accustomed to spoon-fed rainfall all year.

Drying grain and test weight have a correlation that we also need to keep in mind as we harvest wetter than normal grain and test weights appear light. As grain is dried down to storable moisture levels, it will actually pick up bushel weight. According to Iowa State University, in general you can gain 1/4 pound back for every 1% moisture taken out. So for example, a sample is testing 23% moisture and weighing 52 pounds. Drying this corn from 23 down to 15% will add approximately 2 pounds to get a 54 pound sample. Grain dried rapidly with high heat (>150 degrees F) it is not as likely to pick up that 1/4 pound per 1% moisture. Grain dried slowly with lower heat (<150 degrees F) may pick up a bit more than 1/4 pound per point of moisture.

Storing grain that is immature or light test weight (<54 pounds) is a bit more difficult as well because it usually has more physical damage. Screening grain to remove foreign material and fines may be beneficial to increase air flow for uniform drying and storage. Be sure the grain is dried down to at least 15% moisture to inhibit mold and toxins from growing. Once grain is in storage, plan on moving lower quality grain prior to the onset of warmer spring weather if possible. Immature, lower test weight grain typically has a storage life half that of normal grain. Monitoring grain in the bin every two weeks is essential to make sure it stays in condition.

Genetic differences in test weight often Family B can be noticed in the field. AgriGold Family F Hybrids will have heavier test weight and better grain quality compared to Family B Hybrids. As you can see in the picture, Family B hybrids have a much larger kernel compared to the Family F hybrid. Even though test weight is less, yields are often extremely good with family B products in years like 2009.

Categories: Corn Harvest

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