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ISSUE 12  July 20, 2000



    Even though included in past pest reports, the requests for information on estimating yield keep pouring in.

    Estimating yield in wheat, or any crop, is done based on the components that compose yield and only determines potential; crop yield is determined after harvest. Small errors in counting the components that contribute to yield can result in large errors in the yield estimate.

    Yield in small grains is the sum of three components: i) the number of heads in a unit area; ii) the number of kernels that are produced on a head; and iii) the weight of each of those kernels. Kernel weight can not be determined until harvest so a historical average must be used.


bu/A= (heads/3ft X spikelets/head X kernels/spikelet X 0.142*)
                              row spacing (inches)

* Conversion factor that incorporates area, kernel weight and volume.


Using the formula:

    1. Determine the number of heads in three feet of row. Small heads with two or three kernels should not be counted; they will result in biased high yield estimate.

    2. Determine the number of spikelets per head. This should be an average of six or more randomly selected heads. Top and bottom spikelets contribute little to overall yield and should not be counted (Figure 1).

    3. Determine the average number of kernels per spikelet. Small errors in this number result in unrealistically high yield estimates; consequently, using a fixed number that accurately reflects long term yield trends is best. Usually 2.3 gives the most accurate results, or 2.1 when the crop has been stressed.

    4. Finally determine the drill row width. When unknown simply measure the distance between several rows of plants and use the average. Most double disc drills are set at 6, 7, or 8 inch row spacings. Air seeders place seed in bands that can range from three to five inches wide; in this case the band width plus distance between bands is used. Measure several rows from the left side of the band to the left side to determine the width.

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Figure 1.  Wheat spike, arrows indicate which spikelets do not contribute significantly to yield and should not be included in number of spikelets per head when calculating yield.


    As illustrated yield estimates are subjective. The correlation between an estimate and the final yield is related to how close head and kernel counts are to the real numbers and crop development during the remainder of the growing season. Keep in mind that no field is uniform and the yield potential varies tremendously within a single field. To get accurate counts the process should be repeated several times, not less than eight per field.

Happy counting.

Michael D. Peel
Small Grains Extension Agronomist



    Just when you thought GPS (global positioning system) was taking longer to incorporate into cost-effective systems, the uses begin springing up all over in agriculture and beyond. Besides mapping your soils, fertility needs, disease prevalence and weed populations, GPS has moved into hearth and home. If your new car has a GPS receiver, there is a network of satellites tracking
your route. If the car has a LoJack- transmitter, the signal that comes from this device can be used by the police if the car is ever reported stolen. Pets can now get chipped. In other words, a tiny microchip is inserted under their skin with a syringe so that if they are lost they can be tracked and found. With a new mandate from the Federal Communications Commission, all cellular phones sold next year must be able to identify their locations for emergency purposes. These phones, too, will be embedded with tiny, microchip-based processors or Internet-based systems that rely on GPS technology to pinpoint locations. These signals will be received directly from the chips or through a Web network. Within a year, this same technology will be available in watches and necklaces that can be worn by children or Alzheimer s patients. Other new devices in the works include: personalized maps for the dashboard of your car; anti-theft systems; boat and airplane tracking devices; and locator
systems for mapping the movement of migratory animals.

    In crop agriculture, GPS has already proven itself and rapid application of the technology is becoming more and more a reality. Aerial photography, mapped according to GPS location, is visually useful to identify low, wet areas in fields, erosion problems in crops, and create a snapshot of problems during the cropping season. Indiana agronomist, Bob Nielsen, recently pulled together several Web locations that might provide opportunities for using the new technologies for locating and diagnosing crop problem areas. Some of these sites include: find out about using kite, yes kite, aerial photography
through a Web site that talks about adapting this technology to crop scouting at:


(remember several years ago when model planes were used to take snapshots or spray small areas?); find out about using aerial photos even without GPS at Purdue’ s site at:


or add the GPS referenced aerial photos to your farm maps by using one of the many providers such as Earthscan at:


find out more on using your DGPS (digital global positioning system) from your combine during the scouting season by hooking a palm computer with GIS (global information system) software and a hard-framed backpack to map problem areas by foot or ATV (all terrain vehicle) at:


also look at the array of GIS mapping software recently available such as StarPal HGIS at:


or ESRI’s ArcPad at:


or any of the multitude of other programs currently in use. With the recent decision to eliminate the GPS selective availability by the U.S. federal government, the improved accuracy from satellite signals has allowed recreational GPS navigation receivers such as Garmin and Magellan and others can now be used for field scouting although still limited on how close you can actually target a specific location. These devices do allow general points to be pinpointed later.

    As was recently mentioned in the Dell Home Systems Co. magazine for computer users (at http://www.dell4me.com/browser), it is easy to imagine the day when you ve got your cell phone with GPS and wireless protocols and you re walking down the nearby city street close to dinner time after running some errands in town. The phone starts to chirp and when answered or viewed you see that it s a message from the Chinese restaurant down the street telling you to come on in for half off your dinner tab. The restaurant identified a potential customer because of the GPS and
demographic information about cell phone owners that the restaurant owners bought from the cell phone company that gave its phones away in a recent promotion. Possible? It may not be too far off. So, can you imagine the face of the new farms in only five years? What a difference a mere year makes in our lives today.

Denise McWilliams
Extension Crop Production Specialist

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