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Corn Harvest Quality Report 2014/2015

Contents

  1. Harvest Quality Highlights
  2. Introduction
  3. Quality Test Results
  4. Moisture
  5. Chemical Composition
  6. Physical Factors
  7. Mycotoxins
  8. Crop and Weather Conditions
  9. Planting and Early Growth Conditions - Spring (March - May)
  10. Pollination and Grain Fill Conditions - Summer (June - August)
  11. Harvest Conditions (September - October +)
  12. Comparison of the 2015 Average to the 2014, 2013, and 4YA
  13. Corn Production, Usage, and Outlook
  14. U.S. Corn Use and Ending Stocks
  15. Outlook
  16. Survey and Statistical Analysis Methods
  17. Survey Design and Sampling
  18. Statistical Analysis
  19. Testing Analysis Methods
  20. Corn Grading Factors
  21. Moisture
  22. Chemical Composition
  23. Physical Factors
  24. Mycotoxin Testing
  25. U.S. Corn Grades and Conversions
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D.Physical Factors

Physical factors include other quality attributes that are neither grading factors nor chemical composition. Tests for physical factors provide additional information about the processing characteristics of corn for various uses, as well as its storability and potential for breakage in handling. The storability, the ability to withstand handling, and the processing performance of corn are influenced by corn’s morphology. Corn kernels are morphologically made up of four parts, the germ or embryo, the tip cap, the pericarp or outer covering, and the endosperm. The endosperm represents about 82% of the kernel, and consists of soft (also referred to as floury or opaque) endosperm and of horneous (also called hard or vitreous) endosperm, as shown to the right. The endosperm contains primarily starch and protein, the germ contains oil and some proteins, and the pericarp and tip cap are mostly fiber.

SUMMARY: PHYSICAL FACTORS

  • U.S. Aggregate average stress cracks and stress crack index (SCI) in 2014 were slightly lower than in 2013 but higher than 3YA for each factor, indicating corn’s susceptibility to breakage will be similar to or slightly less than last year. Among the ECAs, the Southern Rail ECA has had the lowest SCI in 2014, 2013, 2012 and for 3YA. The Southern Rail ECA also had the lowest stress crack percentages in 2013, 2012 and for 3YA.
  • U.S. Aggregate average 100-k weights (34.03 g) in 2014 were higher than in 2013 (33.41 g) and for 3YA (33.69 g), but were lower than the drought year of 2012 (34.53 g).
  • Average kernel volumes (0.27 cm3) for the U.S. Aggregate in 2014 were the same as those in 2013, 2012 and 3YA (all 0.27 cm3).
  • Of the ECAs, the Pacific Northwest had lowest kernel volume and 100-k weights in 2014, 2013 and for 3YA.
  • Kernel true densities averaged 1.259 g/cm3 for U.S. Aggregate corn in 2014, which was nearly same as 1.258 g/cm3 in 2013, close to 1.267 g/ cm3 for 3YA, but significantly lower than 1.276 g/ cm3 in 2012.
  • Fewer kernels were distributed with true densities above 1.275 g/cm3 indicating softer corn in 2014 than in 2012 but similar to 2013.
  • Of the ECAs, the Pacific Northwest had the lowest true density and lowest test weights in 2014, 2013 and for 3YA.
  • Whole kernels averaged 93.6% for U.S. Aggregate corn, which was higher than 92.4% in 2013 but nearly the same as 93.5% for 3YA.
  • Horneous endosperm averaged 82% for U.S. Aggregate corn in 2014, the same as 82% in 2013, significantly lower than 85% in 2012 and lower than 84% for 3YA. Horneous endosperm was similar to 2013 but softer than that found in the drought year, 2012.
  • The factors including horneous endosperm, true density and test weight appear to change in the same direction, with higher values in a drought year (2012) and lower values in a high-yielding year (2014). The multiple survey results indicate kernel volumes stayed relatively constant between drought and high-yielding years.

The following tests reflect these intrinsic parts of the corn kernels, in addition to the growing and handling conditions that affect corn quality.

1. Stress Cracks

Stress cracks are internal fssures in the horneous (hard) endosperm of a corn kernel. The pericarp of a stress-cracked kernel is typically not damaged, so the outward appearance of the kernel may appear unaffected even though stress cracks are present. The cause of stress cracks is pressure buildup due to large moisture and temperature gradients within the kernel’s horneous endosperm. This can be likened to the internal cracks that appear when an ice cube is dropped into a lukewarm beverage. The internal stresses do not build up as much in the soft, floury endosperm as in the hard, horneous endosperm; therefore, corn with a higher percentage of horneous endosperm is more susceptible to stress cracking than softer kernels. A kernel may have one, two, or multiple stress cracks. High-temperature drying is the most common cause of stress cracks. The impact of high levels of stress cracks on various uses includes:

  • General: Increased susceptibility to breakage during handling, leading to increased broken corn needing to be removed during cleaning operations for processors, and possible reduced grade.
  • Wet Milling: Lower starch yield because the starch and protein are more difficult to separate. Stress cracks may also alter steeping requirements.
  • Dry Milling: Lower yield of large flaking grits (the prime product of many dry milling operations).
  • Alkaline Cooking: Non-uniform water absorption leading to overcooking or undercooking, which affects the process balance.

Growing conditions will affect crop maturity, timeliness of harvest, and the need for artificial drying, which will influence the degree of stress cracking found from region to region. For example, late maturity or late harvest caused by weather-related factors such as rain-delayed planting or cool temperatures may increase the need for artificial drying, thus potentially increasing the occurrence of stress cracks.

Stress crack measurements include stress cracks (the percent of kernels with at least one crack) and stress crack index (SCI), which is the weighted average of single, double and multiple stress cracks. Stress cracks measure only the number of kernels with stress cracks, whereas SCI shows the severity of stress cracking. For example, if half the kernels have only single stress cracks, stress cracks are 50% and the SCI is 50. However, if all the cracks are multiple stress cracks, indicating a higher potential for handling breakage, stress cracks remain at 50% but the SCI becomes 250. Lower values for stress cracks and the SCI are always better. In years with high levels of stress cracks, the SCI is valuable because high SCI numbers (perhaps 300 to 500) indicate the sample had a very high percent of multiple stress cracks. Multiple stress cracks are more detrimental to quality changes than single stress cracks.

RESULTS

  • Stress cracks of U.S. Aggregate corn averaged 8% in 2014, which was below 9% in 2013 but higher than 4% in 2012 and 5% for 3YA.
  • U.S. Aggregate stress cracks standard deviation was 9% in 2014 compared to 10% in 2013 and 6% for 3YA.
  • Stress cracks ranged from 0 to 100% in 2014, whereas the ranges were from 0 to 86% and 0 to 63% in 2013 and 2012, respectively.
  • Stress cracks distribution in 2014 showed 79.3% of samples with less than 10% stress cracks (80.0% in 2013 and 91% in 2012). In 2014, there were 9.2% with stress cracks above 20%, which is below the 11% in 2013 but much higher than the 3% in 2012. Stress crack distributions indicate the 2014 corn had similar or slightly lower susceptibility to breakage than that found in 2013.
  • Stress cracks averages for the Gulf, Pacific Northwest, and Southern Rail ECAs were 9%, 6% and 6%, respectively.
  • SCI had a U.S. Aggregate average of 20.2, which is less than 22.8 in 2013 but significantly higher than 9.3 in 2012.
  • U.S. Aggregate SCI standard deviation in 2014 was 27.7, compared to 35.1 in 2013 and 18.4 for 3YA.
  • The SCI had a range of 0 to 410, which is wider than the range in 2013 (0 to 324) and 2012 (0 to 217).
  • Of the 2014 samples, 88.4% had SCI of less than 40, which is higher than the 86.0% of the 2013 samples. While the percentage of 7.2% of the 2014 samples that had SCI greater than 80 is similar to the 9.0% in 2013, the proportion is higher than the 2.0% in 2012. This distribution may indicate more artificial drying was likely done in 2014 and 2013 than in 2012. However, SCI distributions for 2014 indicate similar or slightly lower numbers of kernels with multiple stress cracks than for 2013.
  • SCI averages for the Gulf, Pacific Northwest, and Southern Rail ECAs were 24.1, 12.8 and 11.4, respectively. The 3YA for SCI by ECA was also lowest for the Southern Rail ECA.
  • The Southern Rail ECA had the lowest stress cracks and SCI of the ECAs in 2014, 2013 and 2012, and for 3YA with the exception of having the same stress crack levels as in the Pacific Northwest ECA in 2014. The lower stress cracks and SCI found for the Southern Rail ECA is likely related to greater field drying potential that is typically found in the states comprising the Southern Rail ECA.

2. 100-Kernel Weight

100-kernel (100-k) weight indicates larger kernel size as 100-k weights increase. Kernel size affects drying rates. As kernel size increases, the volume-to-surface area ratio becomes higher, and as the ratio gets higher, drying becomes slower. In addition, large uniform-sized kernels often enable higher flaking grit yields in dry milling. Kernel weights tend to be higher for specialty varieties of corn that have high amounts of horneous (hard) endosperm.

RESULTS

  • 100-k weights of U.S. Aggregate samples averaged 34.03 g in 2014, which was significantly higher than 33.41 g in 2013, significantly lower than 34.53 g in 2012, and higher than 33.69 g for 3YA.
  • U.S. Aggregate 100-k weight standard deviation of 2.83 g in 2014 was close to 2.88 g in 2013 and 2.76 g for 3YA.
  • 100-k weight ranges were slightly lower in 2014 (19.70 to 46.30 g) compared to 2013 (18.07 to 45.09 g) and 2012 (17.49 to 45.39 g).
  • The 100-k weights in 2014 were distributed so that 41.2% of the samples had 100-k weights of 35 g or greater, compared to 39% in 2013 and 48% in 2012.
  • 100-k weights were lowest for the Pacific Northwest ECA, with 30.92 g compared to the Gulf and Southern Rail ECAs that averaged 34.88 g and 34.47 g, respectively. The Pacific Northwest ECA also had the lowest 100-k weights in 2013 and for 3YA.

3. Kernel Volume

Kernel volume in cm3 is often indicative of growing conditions. If conditions are dry, kernels may be smaller than average. If drought hits later in the season, kernels may have lower fill. Small or round kernels are more difficult to degerm. Additionally, small kernels may lead to increased cleanout losses for processors and higher yields of fiber.

RESULTS

  • Kernel volume averaged 0.27 cm3 for U.S. Aggregate corn in 2014, which was unchanged from 0.27 cm3 in 2013 and 2012 and for 3YA.
  • The standard deviation for U.S. Aggregate kernel volume remained constant at 0.02 cm3 for 2014, 2013, 2012 and 3YA.
  • Kernel volumes ranged from 0.16 to 0.36 cm3 in 2014, 0.15 to 0.36 cm3 in 2013 and 0.14 to 0.35 cm3 in 2012.
  • The kernel volumes in 2014 were distributed so that 15.1% of the samples had kernel volumes of 0.3 cm3 or greater, compared to 15% in 2013 and 11% in 2012.
  • Kernel volumes for the Gulf, Pacific Northwest and Southern Rail ECAs averaged 0.28 cm3, 0.25 cm3, and 0.27 cm3, respectively.
  • The Pacific Northwest ECA had lower kernel volumes than the other two ECAs in 2014, 2013 and for 3YA.

4. Kernel True Density

Kernel true density is calculated as the weight of a 100-k sample divided by the volume, or displacement, of those 100 kernels. True density is a relative indicator of kernel hardness, which is useful for alkaline processors and dry millers. True density, as a relative indicator of hardness, may be affected by the genetics of the corn hybrid and the growing environment. Corn with higher density is typically less susceptible to breakage in handling than lower density corn, but it is also more at risk for the development of stress cracks if high-temperature drying is employed. True densities above 1.30 g/cm3 would indicate very hard corn desirable for dry milling and alkaline processing. True densities near the 1.275 g/cm3 level and below tend to be softer, but will process well for wet milling and feed use.

RESULTS

  • Kernel true density averaged 1.259 g/cm3 for U.S. Aggregate corn in 2014, which was similar to 1.258 g/ cm3 in 2013, significantly lower than 1.276 g/cm3 in 2012 and lower than 1.267 g/cm3 for 3YA.
  • The true density standard deviation for U.S. Aggregate corn was 0.020 g/cm3 in 2014, 0.021 g/cm3 in 2013, 0.017 g/cm3 in 2012, and 0.019 g/cm3 for 3YA.
  • True densities ranged from 1.160 to 1.340 g/cm3 in 2014, 1.157 to 1.326 g/cm3 in 2013, and 1.199 to 1.332 g/cm3 in 2012. Kernel true densities in 2014 were distributed so that only 30.2% of the samples were at or above 1.275 g/ cm3, compared to 34.0% of the samples in 2013 and 52.0% in 2012. Since values above 1.275 g/cm3 are often considered to be hard corn and those below soft corn, this kernel distribution indicates a higher percentage of samples with lower true density than in 2012 but was similar in softness to 2013.
  • In 2014, kernel true densities for the Gulf, Pacific Northwest and Southern Rail ECAs averaged 1.262 g/ cm3, 1.246 g/cm3, and 1.263 g/cm3, respectively. Pacific Northwest true densities, in addition to test weights, were lowest among ECAs in 2014 and 2013 and for 3YA.
  • Similarly, test weight was significantly lower in 2014 (57.6 lb/bu) than in 2013 (57.9 lb/bu) and 2012 (58.8 lb/bu). The adjacent figure illustrates the positive relationship between kernel true density and test weight for the 2014 samples.

5. Whole Kernels

Though the name suggests some inverse relationship between whole kernels and BCFM, the whole kernels test conveys different information than the broken corn portion of the BCFM test. Broken corn is defined solely by the size of the material. Whole kernels, as the name implies, is the percent of fully intact kernels in the sample with no pericarp damage or kernel pieces chipped away.

The exterior integrity of the corn kernel is very important for two key reasons. First, it affects water absorption for alkaline cooking and steeping operations. Kernel nicks or pericarp cracks allow water to enter the kernel faster than intact or whole kernels. Too much water uptake during cooking can result in loss of solubles, non-uniform cooking, expensive shutdown time and/or products that do not meet specifications. Some companies pay contracted premiums for corn delivered above a specified level of whole kernels.

Second, fully intact whole kernels are less susceptible to storage molds and breakage in handling. While hard endosperm lends itself to preservation of more whole kernels than soft corn, the primary factor in delivering whole kernels is harvesting and handling. This begins with proper combine adjustment followed by the severity of kernel impacts due to conveyors and number of handlings required from the farm field to the end user. Each subsequent handling will generate additional breakage. Harvesting at higher moisture contents (e.g., greater than 25%) will usually lead to more pericarp damage to corn than harvesting at lower moisture levels (less than 18%).

RESULTS

  • Whole kernels averaged 93.6% for U.S. Aggregate corn, which was significantly higher than 92.4% in 2013, significantly lower than 94.4% in 2012, and similar to 93.5% for 3YA.
  • The whole kernel standard deviation for the U.S. Aggregate was 3.5%, which was lower than 3.7% for 2013 and 3YA, but similar to 3.4% for 2012.
  • Whole kernels ranged from 63.6% to 99.8% in 2014, 73.6 to 99.6% in 2013 and 68.0 to 100% in 2012.
  • Of the 2014 samples, 85.7% had 90% or higher whole kernels, compared to 77% in 2013 and 90% in 2012.
  • Whole kernels averages for Gulf, Pacific Northwest, and Southern Rail were 93.8%, 92.5%, and 93.9%, respectively. Whole kernels were lowest for Pacific Northwest (92.5%) in 2014, but the 3YA of each ECA illustrates there was little variation among the ECAs.

6. Horneous Endosperm

The horneous endosperm test measures the percent of horneous or hard endosperm, with a potential value from 70 to 100%. The greater the amount of horneous endosperm relative to soft endosperm, the harder the corn kernel is said to be. The degree of hardness is important depending on the type of processing. Hard corn is needed to produce high yields of large flaking grits in dry milling. Medium-high to medium hardness is desired for alkaline cooking. Moderate to soft hardness is used for wet milling and livestock feeding.

Hardness has been correlated to breakage susceptibility, feed utilization/efficiency and starch digestibility. As a test of overall hardness, there is no good or bad value for horneous endosperm; there is only a preference by different end users for particular ranges. Many dry millers and alkaline cookers would like greater than 90% horneous endosperm, while wet millers and feeders would typically like values between 70% and 85%. However, there are certainly exceptions in user preference.

RESULTS

  • Horneous endosperm averaged 82% for U.S. Aggregate corn in 2014, which was the same as 82% in 2013, significantly lower than 85% in 2012, and lower than 84% for 3YA.
  • U.S. Aggregate standard deviation for horneous endosperm was 4%, the same as in 2013 and 2012 and for 3YA.
  • Horneous endosperm ranged more widely in 2014 (71 to 97%) than in 2013 (71 to 96%) and 2012 (74 to 97%).
  • Of the 2014 samples, 62.1% were equal to or greater than 80% horneous endosperm, which was below 67% in 2013 and far below 86% in 2012.
  • Horneous endosperm averages for Gulf, Pacific Northwest, and Southern Rail were 82%, 81%, and 82%, respectively. Of the ECAs, the Pacific Northwest was lowest in horneous endosperm in 2014 and 2013, and for 3YA.
  • As mentioned in the true density section, the Pacific Northwest ECA was lowest in true density in 2014, 2013 and for 3YA. The adjacent figure shows the weak but positive relationship (a correlation coefficient of 0.74) between horneous endosperm and true density for the 2014 samples.