Yield Monitor Pocket Guide

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Yield monitors are a mature technology which allow producers to quantify local yield variations caused by soil properties, fertility management, weather, or other crop management factors. By recording instantaneous yield along with a GPS location, yield monitors produce a visual indication of yield trends across fields. When collected and analyzed over multiple years, yield data can support changes in crop management practices that result in increased yields and reduced yield variability.

This pocket guide is intended to serve as a reference for general yield monitor operation and calibration. This guide will help you implement best management practices for using yield monitoring systems and steer you away from common yield monitoring mistakes.

Yield monitor estimated volume map

Pre-harvest Checklist

The following steps are recommended before grain harvest begins to ensure that your yield monitor is ready for the new season:
  • Inspect your clean grain elevator chain and the mass flow sensor at the top of the clean grain elevator. Make sure that the chain is tight and does not show excessive wear. Check behind and around the mass flow sensor to make sure the sensor is free to move.
  • Inspect the wiring attached to the mass flow sensor at the top of the clean grain elevator. Make sure the wire is not touching any surfaces that may wear or break the wire. If needed, reroute the wire or use additional zip-ties to securely mount the wire. Make sure the connector is able to freely move and is not in tension.
  • Inspect the moisture sensor to ensure that it is functional. If grain was left in the moisture sensor from a previous harvest you should clean out the sensor and ensure that all moving parts are able to freely and easily move.
  • Turn the combine on and startup the yield monitor display. Move the combine outside and into an area where it has a good view of the sky. Complete the following tests:
    • Make sure that the yield monitor is recognized on the display. If any errors are reported or if any of the sensors are not responding then you should check the wiring to each sensor. Wires may have broken or damaged by a rodent or other cause during storage.
    • Confirm that the GPS receiver is working and is reporting a valid GPS location to the yield monitor display.
  • Prepare your yield monitor display for the new season by following these steps:
    • Remove the data card from the display and make sure that the previous year’s harvest data has been removed.
    • Setup a new harvest season on the display.
    • Preload the field names that you will harvest this year. This can be done either by importing field names from a previous year or by loading field names from your office computer. Taking the time to preload the field names eliminates naming errors during harvest.
    • Preload the names of hybrids and varieties that you will harvest this year. These can also be entered into the display manually or loaded onto the display’s data card from your office computer.
    • Lookup the current firmware version of your display. Ask your dealer if a newer firmware version is available and if so update the firmware before harvest.
  • Calibrating your yield monitor is one of the first tasks you should perform each harvest season. Make sure to identify a field early in your harvest season that can provide a uniform calibration environment.
  • Review the combine operator’s manual to refresh your memory on the proper calibration procedure for your combine.

Yield Monitor Components

Mass Flow Sensor: The mass flow sensor measures the amount of grain flow through the combine. Although different styles exist, the most common type is an impact plate sensor located at the top of the clean grain elevator. The mass flow sensor deflects as grain impacts the plate and the amount of deflection is related to grain flow. When properly calibrated these sensors can be within 1 to 3% accurate.

Moisture Sensor: The moisture sensor captures a subsample of the crop flow and determines the real time crop moisture. This information is used to calculate the dry basis crop yield. Moisture sensors typically update the crop moisture at a rate of once every 10 to 20 seconds. Moisture sensors should be recalibrated throughout the year as crop conditions change.

GPS Receiver: The GPS receiver facilitates creating a yield map by providing a physical location for each crop flow reading. The accuracy of GPS receivers will vary based on the type of correction service used, but for yield monitoring WAAS GPS correction is suitable. The GPS receiver typically connects directly to the display and can also be used to support autoguidance applications.

Display or Task Computer: The display serves several functions within a yield monitoring system including: providing a visual interface for the user, storing yield data to a removable storage disk, managing sensor calibration, and diagnosing any sensor problems. Farm and field names can be uploaded to the display and reused each year to simplify infield setup.

Secondary Sensors: Several secondary sensors exist on a complete yield monitoring system to help ensure quality data collection. First, a header height sensor is required to start and stop data collection when entering or leaving headland areas. The threshold height for data collection is set through the display.

A separator speed sensor is also required to confirm that the combine is currently engaged in a harvest operation. This prevents faulty data from being collected while the combine is in transport mode. The final secondary sensor is a ground speed radar or wheel pickup sensor. This sensor is needed if the vehicle speed is not provided by the radar.

The display will provide diagnostics support to these secondary sensors to help determine if a sensor fault exists.

Yield Data Cards

Yield data collected during harvest is stored internally on the yield monitor display. Data cards are used to transfer the yield data from the display to a computer for analysis. Three typical categories of data cards exist:

  • PCMCIA: Large format data cards commonly used in early yield monitor systems. These cards can be replaced with a PCMCIA-to-Compact Flash adapter.
  • Compact Flash: Small format data card primarily used with current yield monitoring systems. Provides stronger compatibility with consumer electronics.
  • USB Flash Drive or Thumb Drive: Most common format for yield monitor displays introduced after 2009. Eliminates the need for a specialized card reader to extract the data.

Preparing for a New Season: Make sure your data card is ready to go for the new harvest season by following these steps:

  • Backup and remove previous season’s harvest data.
  • Download software updates for your yield monitor to your memory cards.
  • If you use a computer to manage your yield data you can upload your farm and field management tree to your data card to reduce in-cab setup time.

You would never take your combine to the field without proper off-season maintenance. Yield data is a critical decision making tool and pre-season steps are required to ensure that quality data is captured.

Firmware Updates

Firmware Upgrade: Yield monitor manufacturers will typically release firmware updates for displays and other yield monitor components twice per year. These updates are intended to fix problems or bugs in the display software or add new features to the display. In order to ensure the best performance you should install available firmware updates before each harvest season.

Firmware updates can be downloaded from the internet directly to the display’s memory card. When the memory card is inserted into the display you can update not only the display firmware, but also any other electronic unit that is connected to the display. For example, this may allow you to update the software that resides directly on the moisture sensor from the cab of the combine.

Listed below are website addresses for accessing firmware for common precision ag products. Refer to the owner’s manual for model specific installation instructions.

Ag Leader: www.agleader.com/customer-support/downloads/

AGCO: www.agcotechnologies.com/naen/downloadcentre.htm

CNH: Available from your Case IH or New Holland dealer

Deere: stellarsupport.deere.com/en_US/support/greenStarSystem.html

Measuring Grain Flow

Basic Operation: The mass flow sensor is used to estimate the average grain flow entering the combine grain tank. The path of flow through the combine will cause delays between when the grain enters the head of the combine and when it reaches the mass flow sensor. As grain enters the combine header it must pass through the feeder house, threshing system, cleaning system, cross flow auger, and clean grain elevator before reaching the mass flow sensor. On average these delays are 12—14 seconds between entering the head and reaching the mass flow sensor.

Diagram of measuring grain flow through a combine.

The reverse situation occurs as combines exit a crop. The flow rate of grain at the mass flow sensor will gradually decline as the combine finishes the threshing operation.

The result of gradual grain flow through the combine is inaccurate yield results and lost mapping resolution of yield response across waterways and other areas where rapid yield changes occur.

Disengaging the Yield Monitor

The mapping system should be disabled when the combine is not engaged with a crop. Disengaging the mapping system is accomplished by raising the crop header above a predefined threshold or by turning off the threshing system.

Calibration: The header height sensor must be calibrated to identify the specific height that will disengage the system. The procedure varies by manufacturer, but the user is often able to set different height thresholds for specific crop headers. The maximum height should be set at a comfortable level for travel on the headlands and often is not the full maximum height achievable by the combine.

Small areas of low yield are caused by grain flow lag through the combine.

Yield monitor map showing grain flow lag.

Significant mapping errors occur when the header is not properly raised at the end of each pass to disengage the yield mapping system.

Yield monitor mapap showing significant mapping errors.

Setting up Your Yield Monitor

Before starting each field the operator needs to provide basic field information to the yield monitor display. Typically this includes:

  • Operator name
  • Grower name
  • Farm name
  • Field name
  • Field region name/number
  • Machine description including both combine and header information

When operating more than one combine in a single field it is important to correctly label the Grower/Farm/Field names so that the two yield maps can be incorporated into a single file.

Additionally, most precision ag yield monitors will allow the operator to import a list of all Grower/Farm/Field names. This helps reduce the amount of setup time in the combine by eliminating any direct typing on the display.

Before the start of every season make sure you have a correctly formatted data card and that any software updates to the yield monitor have been completed.

Mass Flow Sensor Calibration

The mass flow sensor must be calibrated to ensure accurate yield data. In general the mass flow sensor should be recalibrated anytime there is a significant change in crop conditions. These include the following conditions:

  • After a long period of inactivity such as at the beginning of a new season.
  • Switching between crop types.
  • Significant changes in crop moisture of more than 4%.
  • Significant test weight changes.
  • Changes in crop conditions that cause a shift in normal operating speeds including lodged or downed crops, high moisture crops, or significant changes in ground conditions.

Calibration Procedure: Specific calibration procedures change based on the manufacture, but several general recommendations fit all brands:

  • Calibrate for at least the minimum number of loads recommended by the yield monitor manufacturer.
  • Each calibration load should be at least 3,000 lbs or greater. More than 5,000 lbs is preferred.
  • Calibration loads should be taken as single passes when possible to avoid errors associated with grain flow delay.
  • Each calibration load should be conducted at a different mass flow rate. This can be controlled either by slowing down the maximum speed of the combine or by maintaining a set speed and reducing the active header width.
  • The calibration flow rates should cover the entire range of flow rates that are expected in the target crop.
  • After calibration you can use “regions” or “loads” to monitor the accuracy of the calibration

Moisture Sensor Calibration

The moisture sensor must also be calibrated in order to ensure accurate yield data. Grain moisture data is used to provide a corrected dry grain yield estimate. The moisture sensor should also be recalibrated periodically or when there is a significant change in crop conditions.

Calibration Procedure: Specific calibration procedures change based on the manufacture, but several general recommendations fit all brands:

  • Start a new combine “load”. This will create a new log that can be used to calibrate the grain moisture.
  • Harvest an entire grain tank of grain.
  • Stop the harvester and randomly sample the grain tank from several locations.
  • Record the load moisture from the combine yield monitor.
  • Calculate the actual moisture content of the grain tank sample using an accurate moisture tester. Handheld moisture meters are generally not accurate enough for this measurement unless it has been calibrated against a higher accuracy meter. To reduce errors, record three separate moisture readings from the single grain sample and use the average as the actual moisture.
  • Enter the difference between the actual moisture and the yield monitor load moisture as a moisture offset.

Temperature calibration requires a similar offset adjustment. Make sure to calibrate temperature when the combine is not operating and has been in a constant shaded environment for a couple of hours.

Managing Calibration Curves

Two different styles of calibration curves exist for yield monitoring systems. Single point calibration curves require the user to calibrate grain mass flow at a single normal operating condition and assumes a linear relationship for mass flow versus sensor output. The second approach uses a multi-point calibration curve in which five or more calibration points are used to create the sensor calibration curve. The type of calibration curve depends on the specific manufacturer. Users should refer to their owners manual to make sure they understand the recommended practice for managing calibration data.

It is important to note how both mass flow and moisture calibration values are recorded and applied to your yield data. These can vary by manufacturer and can impact the way previous yield information is calculated.

For example, in John Deere yield monitoring systems when the moisture calibration value is changed it is applied to all future yield data, but previous data is not impacted. In Ag Leader yield monitoring systems when the moisture sensor is recalibrated the new calibration value is applied to all previous data that has not been exported from the monitor. If a completely new moisture calibration is desired in an Ag Leader yield monitor then the current calibration values should be "retired" and a new calibration sequence should be completed.

Example Calibration Procedure

Step 1: Based on previous yield data or experience within a field, select an area that is typically uniform. Calibrating your combine in a uniform area will produce better calibration results.

Map highlighting good and poor calibration zones.

Step 2: Create a new region or load file on the display and tag the new load as a calibration load.

Step 3: Harvest at least 3000 lbs of grain and transfer the grain to a weight wagon or grain cart with scales. Larger samples are better, but never go above the capacity of the combine grain tank. Record the actual weight and start a new region or load within the field. If performing a multipoint calibration, repeat this procedure while harvesting grain at field speeds of 2.5, 3, 3.5, 4, 4.5, and 5 mph.

Step 4: Enter the actual weight of grain harvested into the yield monitor display for each calibration load or region. The mass flow sensor is now calibrated and should not need recalibrated unless crop conditions change significantly.

The example below shows four grain calibration loads entered into an Ag Leader Integra Yield Monitor Display. When you calibrate a yield monitor you are trying to make the best possible estimation of actual yield. The error values show the amount of error in each calibration load. Once the Perform Calibration button is selected the display will report an overall accuracy associated with the new calibration data. This should be less than 3%. If the results are greater than 3% then the calibration procedure should be repeated.

Ag Leader Integra Yield Monitor display.
Ag Leader Integra Yield Monitor display.

How Accurate is My Yield Monitor?

Managing Expectation: When properly calibrated yield monitors should provide an overall accuracy of 1 to 3% of the total grain harvested within a field. Operators should occasionally check the accuracy of the yield monitor by comparing the total mass of grain within a field or load to the amount measured by a calibrated grain wagon or a grain elevator. It is important to make sure that no other combines are loading into the carts and trucks used for this calibration check.

Although yield monitors can be quite accurate on a field basis, they are not intended to replace a weigh wagon for determining the performance of hybrids and varieties in test plots.

When comparing two varieties in a test plot the following table can be used to help determine how much yield difference is required to be confident in the outcome. This table can be used for test plots that harvest between 500 to 800 foot strips. A 50% confidence level indicates that the yield monitor results are just as good as a coin flip with respect to which hybrid performed better.

Minimum Distinguishable Yield Monitor Yields in Test Plotsr

Minimum Distinguishable Yield Monitor Yields in Test Plots

Yield Monitor Accuracy

Calibration Errors: Calibration errors can be caused by both poor calibration methods as well as poor calibration equipment. Additionally, the moisture sensor may loose accuracy if foreign material such as leaves or biomass restricts contact between the grain and the moisture sensing plates. Due diligence by the operator can minimize the impact of calibration errors by catching them early and recalibrating the machine.

Variable Grain Properties: When grain properties such as moisture or test weight for a specific area of a field are well outside of the calibrated range then additional yield monitor errors can occur. These errors typically do not impact the yield measurement on a field level, but can cause measurable errors when evaluating smaller zones or plots. If crop conditions cause the combine to slow down this will directly impact the grain mass flow rate and will lead to yield calibration errors.

Header Width Errors: The yield monitor is setup for a constant width grain head. This can lead to errors in soybeans or small grains when using a platform head. If the operator typically leaves a gap at the edge of the header then the yield monitor should be programmed for the typical cutting width rather than the overall header width.

Rapid Speed Changes: Rapid speed changes usually experienced during the start or end of a harvest pass will cause yield errors by over or under estimating the travel distance associated with a yield point. The best management practice to mitigate this error source is to always be moving when entering a new pass and roll through the end of the pass to minimize speed changes when recording yield data. These errors can also occur when entering or exiting waterways.

Ground Slope: The impact force of grain measured by the mass flow sensor will change if the combine is heading up or down a slope. Steep upwards slopes will cause a reduced yield estimate while heading down slopes will cause an increased yield. Operating on side slopes has a lower impact on yield errors. These errors are difficult to correct and should be taken into consideration when making side-by-side yield comparisons.

Maintenance Problems: Yield monitors that accumulate debris behind the mass flow sensor can result in yield errors. Additionally, poor maintenance on the clean grain elevator which results in either significant mechanical vibrations or poor grain flow through the moisture sensor can negatively impact yield monitor accuracy.

Using Yield Monitors for Hybrid Evaluation

Hybrid Evaluations: Yield monitors can be an excellent source of data for evaluating hybrid performance on a field scale. Precautions should be taken to ensure that outside sources do not bias these comparisons.

Examples of How to Use Field Scale Yield Monitor Data:

  • Create multi-year field averages to determine management zones.
  • Create yield variability maps to assess hybrid response to highly variable soils and terrain.
  • Use field scale side-by-side testing to quantify hybrid response to fertilizers, pesticides, or population rates as well as side-by-side hybrid comparisons.

Poor Uses of Field Scale Yield Monitor Data:

  • Directly compare yield between two fields planted with two different hybrids. Individual fields have a natural yield potential which will bias this comparison.
  • Directly compare yields between two or more hybrids within the same field without random planting throughout the field. Hybrid blocks will naturally have different soil types, slopes, and productivity that will bias results. Additionally, differences in hybrid moisture content and test weigh will bias results.

Using Yield Monitors for Test Plots

Overview: While yield monitors can be excellent tools for field scale evaluation, care must be taken when using these same tools for small scale comparisons such as test plot strips. The following steps will help to improve yield monitor performance in short test strips, but well calibrated weigh wagons are still recommended for greater accuracy.

  1. Operate at normal combine speed. Test plots are often shorter rows which can lead to operators slowing down. The mass flow sensor is calibrated for normal crop flow, so to maintain accuracy the test plot should be conducted under the same conditions.
  2. Conduct rolling starts. To get the combine up to steady state grain flow as quickly as possible make sure the combine is moving at a normal speed when first engaging the crop. This is known as a rolling start.
  3. Be wary of significant moisture differences. If the test plot has significant grain moisture differences (more than 5% differences) then hand samples of the plots should be collected to verify the moisture content. For every 1% error in grain moisture the yield calculation will be off by 2.5 bu/ac.
  4. Avoid changing terrain. If the test plot field has rolling terrain you should harvest all plots in the same direction. This will reduce the impact of field slope on yield data errors.
  5. Maintain an accurate header width. When harvesting a test plot with a platform header be sure to maintain an accurate and consistent cutting width throughout the plot.

Benefit of Yield Monitor Data in Test Plots

Although yield monitors are not well suited for reporting the true grain yield from a short test plot, they are an excellent test plot resource to ensure that other variables did not impact the hybrid comparison. For example, reviewing yield maps from a test plot can indicate if any region of the test plot was biased by soil property or drainage problems. With this knowledge you can determine how much emphasis to put into the test plot data or if some results should be ignored.

To identify these problem areas, check to see if the yield changes significantly within an individual test strip. If so, then there are other variables impacting the quality of the test plot.

Test plot strip map

Post-harvest Checklist

After the harvest season is complete it is important to spend a few hours to download the harvest data and prepare your yield monitor system for long term storage. Basic steps to follow include:

  • Download the harvest data from your yield monitor display. Open the data on your computer or send the data card to your crop consultant for processing. Even if you do not process your data until later in the winter, you want to make sure that you take a quick look at the data and verify that all fields have been downloaded.
  • Make a backup of your data card and store it in a clearly identified location on your computer. Create a new folder on your computer and name the folder with the crop year. Keep data in the appropriate harvest year so that you can recover this data in the future if needed.
  • Clean out the moisture sensor and clean around the mass flow sensor on the combine. Any left over grain will spoil and cause problems during the next year’s harvest. In general it is a good practice to clean out grain from any accumulation zones within the combine at the end of each year.
  • Remove the yield monitor display from the cab. Although these displays are rated for storage in extremely cold temperatures, it is preferred to store the displays over winter in an indoor, temperature controlled facility. Heat and moisture cycling can cause early failure problems of yield monitor displays.

Yield Mapping Applications

Putting your data to work

The winter is an excellent time to analyze your yield data and determine if there are potential areas for improvement. Several software packages are available to help with yield data analysis and crop consultants can also be a valuable resource to gain knowledge from your yield data.

Identify Areas of Yield Variability: Crop yields vary based on many factors. Yield maps can help identify where the areas of high variability are and can help producers begin to identify factors that are driving yield variability. Some common influencing factors include:

  • Soil Type
  • Slope
  • Fertility
  • Compaction
  • Seeding Rate and Variety
  • Water Management
  • Weed and Pest Management

Once the cause of yield variability is knows, actions can be taken to help reduce future losses. These include adding drainage where necessary, placing hybrids in soil conditions that they are better suited for, and implementing site specific soil sampling and variable rate fertilizer technologies.

Additionally, yield maps can help improve long-term record keeping and are an excellent resource to share with land lords

Calibration Reference Guides

John Deere Yield Monitors

John Deere combines use a single point calibration for their mass flow sensor.

  1. John Deere yield monitors are calibrated through the Original GreenStar Monitor system. If a newer GS2 2600 or 1800 monitor is being used you must run the Original GreenStar Monitor application from the GS2 display.
  2. Grain flow calibration is performed for each individual crop. If a crop has not been calibrated an error will be displayed indicating that this crop requires a calibration.
  3. Select the Calibration Mode button to enter the calibration screen and make sure the combine grain tank is empty.
  4. Once the combine is ready to begin harvesting the calibration load press the Start button. The display will indicate that the Yield Calibration is Running.
  5. Begin harvesting the calibration load. Harvest between 3,000 and 10,000 lbs of grain using a consistent header width.
  6. Adjust the combine speed to maintain a constant flow rate of grain. The target flow rate of grain should be similar to the normal operation point of the combine.
  7. After the desired amount of grain has been harvested, return to the calibration screen and press the Stop button.
  8. Empty the grain tank into a calibrated weigh cart and record the actual grain weight for this task.
  9. Enter the actual weight into the yield monitor using the Scale Weight button. After entering this weight the new calibration value will become effective.

Technical writing and support was provided by Dr. Matt Darr, Iowa State University, Agricultural and Biosystems Engineering

Photos and/or information for this pocket guide were provided by the following companies:

  • AGCO Corporation
  • Ag Leader Technology
  • CNH Global Deere and Company
  • Topcon Precision Agriculture
  • Trimble Navigation