When working with sprayers with a wide boom, it is difficult to determine the new position of the sprayer after a turn around. Improper positioning of the sprayer, resulting from inadequate marking of swath, may lead to excessive overlaps and skips that may lead to waste of chemicals or insufficient pest control.
Traditionally, some foam or mechanical marking systems are used to identify the area covered during one pass of a sprayer. Now, this task can be accomplished by using the GPS (Global Positioning System) or perhaps FM radio signal system. To use these systems, first a pass is made running the perimeter of the field. Then, using GPS, the location of the sprayer is recorded in one corner of the field. After entering the swath width of the sprayer in the controller, a pass is made across the field. This first pass of the length of the field establishes the master swath. As the sprayer turns for the second pass, a light bar indicates by a series of lights right and left of center where the sprayer is in relation to the centerline of the master swath.
Sensor for On-the-Go Control of Site Specific Nitrogen Top Dressing
There seems to be general agreement that site-specific application of fertilizers can improve the efficiency of use. The question we have been debating is how the data for nutrient content of the field should be determined, in other words, which method is more practical and economical. The methods used include: a) conventional soil sampling, b) soil analysis by ion-selective electrodes, c) recording the removal of nutrients by the previous crop, and d) computer-aided decision models based on soil properties and weather data. In a recent paper presented at the American Society of Agricultural Engineers (ASAE) meeting in July 1996, researchers from Germany outlined a fifth method for generating data for determining nitrogen need of a crop during the top-dressing period. Their approach was measuring reflected radiation signals from the plant, on-the-go, for nitrogen top dressing. Heege and Reusch (Institute of Agricultural Engineering, University of Kiel, Germany) suggest that the color of plants is usually a good indicator of the nitrogen supply to the plant. With increasing nitrogen supply in the plant, the color changes from yellow-green to blue-green. They recorded the light reflected from plants using a field spectrometer in the spectral range from 450 to 850 nm, which is the visible plus the near infrared range, to determine the nitrogen uptake status of the plant. The spectrometer was located in front of the tractor 6.5 feet above above the soil surface (see Figure below).
A direct, absolute conclusion from the reflectance data to the nitregen requirement is almost impossible because the color of the plant may depend on many other nutrients. Therefore, this approach cannot be used effectively unless all major factors affecting color are isolated and accounted for. Researchers suggest that under healthy crop conditions (the crop is well supplied with other nutrients and disease free), and with a simple calibration of the system, fairly accurate results can be achieved. For calibration, they recommend selecting two points in the field which differ distinctly in the nitrogen supply. At these two points, the nitrogen requirement is estimated by conventional methods. Also recorded at these two points is the reflection. With this information, the system develops a correlation between reflectance and the nitrogen needed. This relation can later be used for site-specific application of nitrogen as the sensor determines light reflectance on-the-go, during actual top-dressing of nitrogen.
Disclaimer
Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.
All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.
Return to CAT News Homepage