Precision Agriculture

January-March 2002

George Cummins , crop specialist

Beginning in the mid-1990's, “Precision Agriculture” was seen as the technology that would shape cutting edge agriculture. Global Positioning Systems (GPS), Geographical Information Systems (GIS) and Variable-Rate Technologies (VRT) were promoted to producers and agri-businesses serving producers. Improved accuracy, efficiency, profitability, decision-making and management were suggested as potential benefits. This project was developed to provide producers and service providers with practical recommendations to realize the potential benefits of this new technology. The unique emphasis was to make cropping decisions based on Integrated Crop Management principles and the information gathered using the GPS/GIS. The demonstration started as a state initiative identified in the Extension 21 program and was conducted for 5 years (the 1997 – 2001 growing seasons.)

A 40-acre site adjacent to the Northeast Research Farm was leased and divided into quadrants and planted in a corn/soybean rotation (two quadrants in corn and two in soybeans each year).The only planned variables the first three years of the project were planting rates in the two corn quadrants (32K and 36K) and row spacing/seeding rates in the soybean quadrants (10” drill/ 200K planting rate and 30” row/ 182K planting rate). The final two years, manure and commercial fertilizer nutrient sources were compared and the row spacing/seeding rate variables in soybeans continued.

Phosphorus (P), potassium (K) and pH data were collected and several soil sampling methods compared - center point, random point and composite within various grid sizes (0.6 acres and 1.1 acres); by soil mapping unit (SMU) within a 10 acre quadrant; and as a composite sample within each 20 acre area. A balance sheet of estimated nutrient removal (drawdown) based on yield was developed and compared to soil test values. The digitized soil survey was imposed on the field site plan maps to localize differences in SMUs and yield potential. Rainfall was monitored at 9 points within the 40 acres for 3 years (1998 – 2000). Planter accuracy was monitored in 1999 using a computerized measuring wheel called a “ Space Cadet” which measures plant population and spacing. The Late Spring Nitrate Test (LSNT) and the Fall Stalk Nitrate Test (FSNT) were used to monitor N utilization and losses. Field scouting was conducted throughout the growing season to document any weed, insect or disease problems. Yields were calculated by quadrant using the combine monitor, strip tests using the load cell scale on the research farm combine and scale weights from the elevator. The ISU Crop Management Database has been used to do an economic analysis for each 1.1 acre grid. Statisticians at ISU and in Kansas have compared the various layers of information with yield to try to establish correlations and identify the factors limiting crop production.

Experiences gained from this project were shared at stand-alone field days; as part of other field days and crop tours; and as an extension presentation at precision ag. and/or crop meetings. Articles on the project have appeared in the Northeast Research Farm Annual Report, the Precision Ag Edition of the ICM Newsletter, and popular farm publications like Agri-News and Iowa Farmer Today. The project was featured as a cover story twice by Wallaces Farmer magazine. Information from this project was used to develop the ISU Precision Ag Display at the 1999 Farm Progress Show and at the 25th Anniversary Field Day at Nashua in 2001.

1 Some of the impact from this project has already been documented in the Success Story for April, 1999, and for January, 2000.

2. The project attracted a larger and a different audience from those that attend regular field days. Follow-up surveys of program participants showed they have more experience with new technologies and services(i.e. computers, email, grid sampling, GPS/GIS and yield monitoring, variable rate application, and crop consulting, etc).

3. Many of our precision ag. program participants came to the Northeast Research Farm for the first time. They are now aware of the precision ag. research, expertise and experience available from ISU Extension. Survey respondents were reassured, “ Knowing ISU is working on GPS/GIS” and since, “Extension has been my source of unbiased opinions and research for over 40 years.”

4. Our experience with differences in soil test results from various sampling methods of an area reflects the findings of research conducted at Iowa State and elsewhere. Results from composite samples across an area seem to be more consistent/predictable than point samples within a particular grid/area. More cores per sample (12 or more) increase predictability and repeatability.
Our experience would support the recommendation to sample by “management areas.”

5. It is difficult to get a “representative sample” of the whole. Whether we're sampling soil (1# out of 2 million# / acre furrow-slice); plant populations, lodging or % barren ( from 1/1000th of an acre); grain moistures (a handful from a grain tank); or whatever, there is considerable room for variation and misrepresentation. There is considerable variation between and within grids which could be partially explained by “sampling error.” In three years we have been able to identify some areas (i.e. old building site, downwind from the gravel road, etc.) which are not representative of the whole and should be avoided when sampling.

6. Scouting data was available in a timely manner. Weed, insect and N deficiency problems could be corrected before they caused economic yield reduction. Wireworm, hop vine borer and ECB damage in corn and white mold (sclerotinia stem rot) in soybeans are examples of scouting data which 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.

7. Anhydrous ammonia toolbars, dry fertilizer/lime and manure spreaders currently in use may compound soil test variability because of non-uniform spread patterns. Calibration, maintenance and adjustment of planting, spreading and spraying equipment is critical to implementing precision agriculture systems.

8. 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.

9. Dust, pollen, moisture, adverse temperatures, loose connections and/or discharged batteries may affect the accuracy and reliability of GPS/GIS equipment. The equipment is right on most of the time – the problem is recognizing when it isn't.

10. Project yields have been equal to or greater than the yields on the research farm and on neighboring commercial farms. Project yields have exceeded the expected yields using the soil survey. Using the information gathered by our crop scout and GPS/GIS we can in some cases identify the limiting factor (s) – i.e. white mold in soybeans, ECB and N losses in corn, uneven and reduced stands, etc. In other cases the limiting factor (s) are not readily apparent or may in fact be contradictory.

11. Human interpretation and decision-making are still required. The precision agriculture technology does not replace management. Scouting and “ground truthing” are invaluable in explaining the raw numbers. In many ways this information is more timely and more useful than the voluminous amounts of data collected by GPS/GIS systems.

12. Producers and agri-business people using these technologies tell us that our experience mirrors their own. Most are convinced that GPS/GIS is a means to an end and not the end itself. The technology is a useful tool in implementing Integrated Crop Management principles and making decisions which are economically and environmentally sound. ost can justify their investment in scouting and ICM decision-making but struggle to justify their investment in GPS/GIS.

13. The two crop specialists who worked most closely with this project gained practical, hands-on experience with these systems. They determined the strengths and limitations of this technology and have gained the confidence to share their observations, concerns and recommendations with producers and agri-businesses trying to implement the new technologies as well as those marketing the equipment and services.

14. The project earned the respect of key campus administrators. Following a 3-year program review, Wendy Wintersteen and Jerry DeWitt stated in an email, “We think that this is the premier in-field precision ag work being done right now in Iowa that has direct application to our producers and it has been delivered in a simple and meaningful way.”

15. Our surveys typically ask our participants to identify, “The 3 most important things I learned today include….?” Typical responses included statements like: “Small scale variability is greater than I thought.” “The most common variable remains the weather and it is uncontrollable.” “Yield monitors are not perfect.” “Precision Ag is not very precise.” And, “Not all precision ag procedures are cost effective.” These comments reflect some of the limitations of precision ag technologies which we observed. They also help explain why interest in GPS/GIS ,VRT and other precision ag technologies has declined in recent years while adoption of ICM strategies has increased. The Precision Ag Demonstration Project results justify these trends.


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