Beginning in the mid-1990s, precision agriculture was considered the technology that would shape cutting-edge agriculture. Global positioning systems (GPSs), geographical information systems (GISs), and variable-rate technologies (VRTs) were promoted to producers and agribusinesses serving producers. Improved accuracy, efficiency, profitability, decision-making, and management were suggested as potential benefits. A project was developed through Iowa State University to provide producers and service providers with practical recommendations to realize the potential benefits of this new technology. The unique emphasis was to base cropping decisions on the 40-acre demonstration site on integrated crop management principles and the information gathered using GPS/GIS. The demonstration was conducted for 5 years (1997-2001 growing seasons).
Soil fertility data were collected and several soil sampling methods compared. Field scouting was conducted throughout the growing season to document crop growth and development and to locate weed, insect, or disease problems. Profitability was determined and the various layers of information gathered were statistically analyzed to establish correlations and identify the factors limiting crop production.
Observations of the demonstration team and survey results from field day participants indicate the following:
- There was considerable variability in the phosphorus (P) and potassium (K) readings within the 40-acre project site, but all tests indicated that no additional P and K were needed for the 5 years of the project for optimum crop yields.
- Differences in soil test results from the various sampling methods used reflected the findings of research conducted at Iowa State University and elsewhere. Results from composite samples across an area seemed to be more consistent or predictable than point samples within a particular grid or area. More cores per sample (12 or more) increased predictability and repeatability. Our experience would support the recommendation to sample by "management areas."
- It is difficult to get a "representative sample" of the whole. Whether sampling soil, plant populations, lodging, percentage of barren plants, or grain moisture, there is considerable opportunity for variation and misrepresentation.
- Scouting data were available in a timely manner. Weed, insect, and nitrogen deficiency problems could be corrected before they caused economic yield reduction. Wireworm, hop vine borer, and European corn borer damage in corn and white mold (sclerotinia stem rot) in soybean are examples of scouting data that provided "ground truthing" to help explain and interpret the data from this demonstration project. Scouting can be done by the producer with little investment in new technologies.
- Anhydrous ammonia toolbars, dry fertilizer/lime, and manure spreaders currently in use may compound soil test variability because of nonuniform spread patterns. Calibration; maintenance; and adjustment of planting, spreading, and spraying equipment are critical to implementing precision agriculture systems.
- Our project experience suggests that combine monitor data at specific points within a field, from small plots or from odd-shaped fields may not be sufficiently accurate or reliable and should be considered suspect.
- Dust, pollen, moisture, adverse temperatures, loose connections, or discharged batteries may affect the accuracy and reliability of GPS/GIS equipment. The equipment is accurate most of the time--the problem is recognizing when it isn't.
- Using the information gathered by our crop scout and GPS/GIS, we can sometimes identify the limiting factor(s), i.e., white mold in soybean, European corn borer and nitrogen losses in corn, and uneven and reduced stands. Sometimes, the limiting factor(s) is not readily apparent or may be contradictory.
- Human interpretation and decision-making are still required. The precision ag technology does not replace management. Scouting and "ground truthing" are invaluable in explaining the raw numbers.
- Producers and agribusiness personel who use these technologies tell us that our experience mirrors their own. Their comments reflect some of the limitations of precision ag technologies that we have observed. These observations perhaps explain why interest in GPS/GIS, VRT, and other precision ag technologies has declined in recent years, whereas adoption of integrated crop managment strategies has increased. The Precision Ag Demonstration Project results justify these trends.
A comprehensive summary of the Precision Agriculture Demonstration Project is available from the Northeast Research Farm by calling (641) 435-4864.
Crop scout Joyce Dolan uses GPS/GIS equipment to record data from the Precision Ag Demonstration Project.
This article originally appeared on pages 42-43 of the IC-488 (5) -- April 15, 2002 issue.