Grain dockage is the percentage of removable material separated from a grain sample during grading or cleaning. It can include weed seeds, chaff, stems, dirt, and other material that can be removed using the applicable cleaning or testing method.
For Agri-Systems customers, understanding dockage can help explain why grain deliveries may receive deductions and why keeping grain clean matters before delivery. To calculate dockage, divide the weight of the material removed by the original sample weight and multiply by 100. For example, removing 20 grams of dockage from a 1,000-gram sample results in 2% dockage. The materials counted as dockage and the testing process can vary by grain and grading standard.
What Counts as Grain Dockage?
Grain dockage is made up of material that can be separated from the main grain using the cleaning or testing method required for that crop. This can include weed seeds, chaff, stems, straw, dirt, and other removable material. The exact materials that count as dockage depend on the grain and the applicable grading standard.
Common Materials Removed as Dockage
Common materials that may be removed as dockage include weed seeds, chaff and straw, stems, and other plant material. Dirt and other removable material may also be included when they meet the grading definition for that grain.
Not everything removed from a grain sample is automatically classified as dockage. The applicable grading rules determine which materials are counted and how they are measured.
Does Dockage Mean the Same Thing for Every Grain?
No. Dockage rules vary by grain, so the same cleaning process should not be applied to every crop. Different grains can have different sieve sizes, cleaning methods, and requirements for determining what qualifies as dockage.
In the United States, USDA/FGIS procedures set the grading standards and testing methods for different grains. For this reason, the dockage procedure used for wheat may differ from the procedure used for corn, soybeans, or another crop. Always use the grading standard that applies to the specific grain being tested.
How Is Grain Dockage Calculated?
Grain dockage is calculated by comparing the weight of the material removed from a grain sample with the weight of the original sample. The basic calculation is:
Dockage % = Weight of dockage removed ÷ Original sample weight × 100
The applicable grading procedure determines which material is included in the dockage measurement. Because dockage rules can vary by grain, the correct testing and cleaning procedure should be used before calculating the percentage.
Grain Dockage Calculation Example
Suppose a grain sample weighs 1,000 grams before cleaning. After the sample is processed, 20 grams of material is removed and classified as dockage.
- Original sample = 1,000 g
- Dockage removed = 20 g
- Calculation = 20 ÷ 1,000 × 100
- Dockage = 2%
This means 2% of the original sample weight was classified as dockage.
Why the Original Sample Weight Matters
The dockage percentage is based on the gross or uncleaned sample weight before the dockage is removed. Using the original weight gives the percentage a consistent starting point and shows how much of the delivered sample was classified as removable material.
For example, if 20 grams of dockage is removed from a 1,000-gram sample, the dockage is 2%, while 980 grams remains after that material is removed. The 2% dockage describes the proportion of the original sample classified as dockage; it is not the same as the amount of clean grain remaining.
How Is Dockage Measured at the Elevator?
When grain is delivered to an elevator, dockage is measured from a sample taken from the load. The sample is cleaned using the method required for that grain, and the material removed is weighed to determine the dockage percentage. The exact sampling, cleaning, and grading procedures can vary by crop and grading system.
How Is a Representative Grain Sample Taken?
A grain sample needs to represent the overall load so the dockage measurement reflects the condition of the grain being delivered. Samples may be collected from different points during unloading or using an approved sampling method, depending on the grading system and facility.
Sample sizes and sampling procedures can vary by grain and grading standard. A larger or more representative sample can help provide a more accurate picture of the material present in the load than a sample taken from only one small portion.
How Is Dockage Removed?
Once a representative sample is collected, the material that qualifies as dockage is separated using the method required for that grain. Common methods include:
- Sieving: Screens or sieves separate material based on size.
- Aspiration: Air removes lighter material such as chaff and some plant material.
- Mechanical dockage testers: Equipment combines sieving and air separation to remove dockage from the sample.
- Hand separation: Some grading procedures require certain materials to be separated manually.
The equipment and process used depend on the grain and the applicable grading procedure.
How Is the Dockage Percentage Determined?
After the dockage has been removed, the separated material is weighed and compared with the original sample weight. The basic calculation is:
Dockage % = Weight of dockage removed ÷ Original sample weight × 100
For example, if 20 grams of dockage is removed from a 1,000-gram sample, the calculated dockage is 2%. The final reported result must follow the grading procedure for that particular grain.
Official dockage procedures can differ by crop, including the equipment, sieves, cleaning steps, and materials that are classified as dockage. For grain being sold through an elevator, the applicable grading standard should be used rather than assuming one procedure applies to every crop.
What Is the Difference Between Dockage and Foreign Material?
Dockage and foreign material both describe material that is not part of the main grain, but they are not always interchangeable terms. Dockage generally refers to material that can be removed from a grain sample using the cleaning or testing method specified for that crop. Foreign material is a broader grading term that can refer to material other than the predominant grain, depending on the applicable standard.
For example, a wheat sample may contain weed seeds, chaff, and other plant material that can be separated during the dockage procedure. Some of that material may be classified as dockage, while other material may be handled as a separate grading factor under the applicable standard.
The distinction matters because grading systems can measure, report, or deduct for these factors differently. A material removed during cleaning is not automatically counted as dockage, and a foreign material measurement does not necessarily equal the dockage percentage. The applicable grading standard for the specific grain determines how each factor is identified and reported.
How Does Dockage Affect Grain Value?
Dockage can affect the value of a grain delivery because it represents material removed from the original sample rather than saleable grain. A higher dockage percentage can mean more material needs to be removed or cleaned before the grain meets the buyer’s requirements, which may affect the amount paid for the load.
Depending on the buyer and grading system, dockage may result in a deduction, cleaning charge, or other adjustment to the delivery value. The exact effect depends on the crop, the amount of dockage, the buyer’s terms, and the applicable market or grading rules.
Farmers should review the dockage figure on their grain ticket along with other grading factors. Understanding the reported percentage makes it easier to see how the load was graded and identify any deductions or charges connected to dockage.
Actual payment and deduction rules are not the same everywhere. Buyers can use different pricing schedules and contracts, so a specific dockage percentage does not automatically mean the same dollar deduction for every grain delivery.
What Causes High Grain Dockage?
High grain dockage usually means more unwanted material is mixed with the harvested grain. The amount can be affected by field conditions, harvest timing, combine settings, and how grain is handled after it leaves the field. Identifying the source can help farmers reduce the amount of material that needs to be removed before delivery.
Weed Seeds and Plant Material
Weed seeds, chaff, stems, leaves, and other plant material can enter the grain during harvest. Fields with heavy weed pressure or crops with more plant residue can result in a higher amount of removable material in the harvested grain.
Poor Harvest Conditions
Wet conditions, lodged crops, excessive crop residue, or harvesting at the wrong moisture level can make it harder to separate grain from unwanted material. These conditions can leave more chaff, stems, weed seeds, and other material mixed with the grain.
Combine and Harvest Settings
Incorrect combine settings can increase the amount of material carried into the grain tank. Settings for the cleaning system, fan, sieves, rotor or cylinder, and other components need to match the crop and harvest conditions. Poor adjustments can allow more unwanted material to remain with the harvested grain.
Grain Handling and Cleaning
Material can also remain in grain when it is moved, stored, or cleaned after harvest. Poorly adjusted cleaning equipment or inadequate separation can leave unwanted material in the grain before delivery. Proper cleaning and handling can help reduce the amount of material that reaches the final grain sample.
What Research Says About Identifying Grain Dockage
Research has shown that machine vision can be used to identify grain kernels and dockage particles based on characteristics such as size, shape, color, and texture. In a 2003 study published in Biosystems Engineering, researchers tested a machine-vision system on five grain types, including barley, wheat, oats, and rye, along with several dockage categories such as broken wheat kernels, chaff, buckwheat, wheat spikelets, and canola. The system analyzed 230 image features and used a neural network to classify the grain and dockage particles.
The researchers found that some grain and dockage particles with clear differences in shape, size, and color could be classified with very high accuracy, while more irregular materials such as chaff were harder to identify. The study shows how imaging technology could support automated grain identification, dockage detection, and cleaning decisions. However, this research tested a specific machine-vision system and should not be treated as the current method for official grain grading. Actual dockage measurements still depend on the applicable grading procedure for the specific crop.
How Can You Reduce Grain Dockage?
Reducing grain dockage starts with keeping unwanted material out of the grain stream during harvest and handling. Farmers can lower dockage by harvesting under suitable conditions, maintaining equipment, and cleaning grain when needed before delivery.
Harvest as Cleanly as Practical
Harvesting under suitable field conditions can help reduce the amount of weeds, chaff, stems, and other plant material collected with the grain. Harvest timing and crop conditions can both affect how much unwanted material enters the grain stream.
Maintain and Adjust Harvesting Equipment
Properly maintained and adjusted harvesting equipment helps separate grain from unwanted material more effectively. Check components such as sieves, cleaning fans, and other separation systems, and adjust them for the crop and current field conditions.
Reduce Foreign Material Entering the Grain Stream
Keep unnecessary plant material and other debris out of the grain stream during harvesting and handling. Regularly checking equipment and correcting separation problems can help prevent excessive material from reaching the grain tank.
Clean Grain When Appropriate
Grain cleaning can remove unwanted material before the grain is delivered. The right cleaning method depends on the type and amount of material present, as well as the grain being handled. Agri-Systems provides grain cleaning equipment and systems designed to help separate unwanted material from harvested grain.
Check Grain Quality Before Delivery
Checking the grain before delivery can help identify excessive dockage and other quality issues early. A representative sample can give you a better idea of the condition of the grain and whether additional cleaning or handling may be appropriate.
Why Grain Dockage Rules Vary by Crop
Dockage rules are not identical for every grain. Each crop has its own grading factors, cleaning requirements, and methods for separating material from the grain sample. Grain size, moisture, foreign material, and other crop characteristics can affect how a sample is tested and graded.
| Grain | Dockage/cleaning considerations | Why the procedure differs |
|---|---|---|
| Wheat | Crop-specific sieving, aspiration, and grading rules | Grain size and grading factors |
| Corn | Crop-specific sieve and hand-cleaning procedures | Moisture and material characteristics |
| Barley | Crop-specific cleaning and grading procedures | Grain and foreign-material characteristics |
| Soybeans | Crop-specific dockage and foreign-material rules | Different grading factors |
Need Better Grain Cleaning and Handling?
If high dockage is affecting your grain quality or delivery value, the right cleaning equipment can help remove unwanted material before grain reaches the elevator. Agri-Systems provides grain cleaning and handling solutions designed for efficient grain processing and separation.
Need help choosing the right grain cleaning system for your operation? Contact Agri-Systems to discuss your grain, handling needs, and equipment options.
Conclusion
Grain dockage is the percentage of removable material found in a grain sample after it is tested and cleaned according to the applicable grading procedure. It is calculated by dividing the weight of dockage removed by the original sample weight and multiplying by 100. For example, 20 grams of dockage from a 1,000-gram sample equals 2% dockage.
Understanding dockage can help farmers review grain quality, identify potential cleaning needs, and better understand deductions or adjustments on a grain delivery. Since dockage rules vary by crop, always use the applicable grading standard and buyer requirements when evaluating a specific grain load.
Frequently Asked Questions
There is no single dockage percentage that is considered good for every grain delivery. Acceptable levels can vary by crop, grading rules, buyer requirements, contract terms, and market conditions. A lower dockage percentage generally means less removable material is present, but the actual effect on payment depends on the applicable grading and pricing rules.
No. Dockage generally refers to material that can be removed from a grain sample using the cleaning or testing method specified for that crop. Foreign material is a separate grading factor in some grain standards. The two terms can overlap in some contexts, but they are not automatically interchangeable.
Higher dockage can affect the value of a grain delivery because more of the original sample consists of material that must be removed rather than clean grain. Depending on the buyer and grading system, this may result in deductions, cleaning charges, or other adjustments. Payment rules vary by crop, buyer, contract, and market.
Yes. Grain cleaning can remove material that may otherwise be included in the dockage measurement. The effectiveness of cleaning depends on the type of unwanted material, the equipment used, and the grain being processed. The final dockage classification still depends on the applicable grading procedure.
Dockage may be determined by the grain elevator, grain buyer, or an authorized inspection or grading process, depending on the applicable grading system. The facility or inspector takes a representative sample, follows the required testing procedure, and reports the dockage according to the applicable grain standard.
