Published at the Chat 'n Chew Cafe, July 2000

Opportunities for Mapping Crop Problem Areas

R.L. (Bob) Nielsen
Agronomy Dept., Purdue Univ.
West Lafayette, IN 47907-1150
Email address:

Near torrential rains continue to create problems for some Indiana corn and soybean fields. Old tile line patterns are appearing. Evidence of broken tile lines is showing. Stunting or death of crops is visually dramatic in the 'wet holes' of fields. River bottom fields have suffered extensive flood damage. Strange patterns of healthy and stunted crops caused by natural soil drainage variability are creating 'modern artwork' for the amusement of airline travelers flying overhead.

Positive thinkers always look for opportunities amidst problems. What opportunities exist for such soggy soil problems?

One opportunity is to take the time and effort to map or otherwise document the boundaries of the problem areas for future reference and, hopefully, reparation. Today's GPS-based technologies offer the type of accurate assistance that makes this mapping exercise possible in a meaningful way.

Aerial Photography

Nothing beats aerial photography to help you visualize problem areas in a field. If you have opportunities locally to contract with a service provider to fly your fields yet this summer, consider doing so to create visual records of crop damage to wet soils for future reference. You can also simply take to the skies yourself with a plain old camera or a digital camera if you have access to a small plane or an ultra-lite and have the nerve to hang your neck out the window/door as the plane flies on its wingtips.

"Go fly a kite!" takes on a new meaning in southeast Nebraska where Rich Douglass of Southeastern Community College is developing agricultural uses for kite aerial photography (KAP). Visit his Web page at to see what he is 'up to' in adapting this technology to crop scouting.

One of our Purdue Extension publications (AY-252, "Aerial Photography as a Crop Management Aid") will help you evaluate the merits and feasibility of non-georeferenced aerial photography as a crop monitoring and management aid. This publication is available from your local Cooperative Extension Service office or on the Web at .

Georeferenced aerial photography goes a step further and gives you an additional layer to incorporate with your yield maps or soil fertility maps in your farm's Geographical Information System (GIS) database. A problem today is that few service providers offer this aerial version of remote sensing for agriculture and, furthermore, the service is pricey. One such provider is Earthscan (URL: ).

Last year we were able to document the areas of severe phytophthera seedling rot with georeferenced infrared imagery in one of our 30 acre fields at the Davis-Purdue Ag. Center in Randolph County. In addition to the image being a disease map of the field, it also serves as an indicator of wet areas in the field.

Phytophthera damage in soy - 1999

Differential GPS (DGPS)

So you've been wondering what else to do with that high-priced DGPS receiver on the top of your combine other than to use it during grain harvest? Spend a little more money for a WindowsCE™ palm computer plus GIS mapping software plus hard-framed backpack and you can use that receiver to map problem areas on foot or by ATV. There are many WindowsCE™ palm computers available on the market today at prices ranging from $400 to $600. See some reviews of these handhelds on the Web at,7267,1500114,00.html .

There are a few user-friendly GIS mapping software programs available for the WindowsCE™ platform. One that I have experience with is StarPal™ HGIS™ (URL: ). The learning curve for using the software is reasonably low and the program is reasonably flexible for use in crop scouting. The cost is $400 to $600. Another program that is being evaluated by some of my colleagues is ESRI's ArcPad™ (URL: ). The cost is $495. Such programs allow you to mark individual points (e.g., tile blowouts), lines (e.g., gullies) and polygons (e.g., perimeters of ponded areas), as well as record actual values for individual data points in the field (e.g., plant population).

Earlier this summer, we used our backpack GPS unit with a WindowsCE™ palm computer and StarPal™ HGIS™ software to map the wet areas of several of our research fields at the Davis-Purdue Ag. Center in Randolph County. The resulting map was reasonably correlated with our phytophthera map of 1999.

The blue areas outlined in the image below are a mixture of spots with standing water, visible soil surface moisture, ruts from the planter, or barren of plants because the area was not planted in the first place due to muddy conditions. The red/white dashed lines represent areas of water flow (some gullies and some simply minor erosion). The depressing part of the exercise was that it required eight hours of walking and/or ATVing by two people to map the 30-acre field.

Wet areas early June 2000

Recreational GPS

The recent decision by the U.S. federal government to eliminate the GPS Selective Availability (aka satellite signal scrambler) means that the accuracy of non-DGPS receivers has improved from hundreds of feet to tens of feet. Now there is some potential for using recreational GPS navigation receivers (Garmin™, Magellan™, etc.) for certain kinds of field scouting. These devices range in price from about $200 to $500.

Garmin III Plus

Several challenges still exist for their use in field scouting. First of all, their current ability to zoom in on a target is limited relative to your detailed geographic needs in a field. Related to the zooming limitation, the constant size of the navigation cursor itself on the screen limits your ability to 'zero in' on a target because the cursor's footprint is too large.

Garmin III Plus closeup

Thirdly, most of these devices limit you to marking 'waypoints' (individual points of interest) or trip routes ('breadcrumb' trails), but not closed boundaries or polygons (e.g., the perimeter of a soggy soil area). Finally, software programs to facilitate data transfer between these devices and a GIS mapping program on your PC are few and far between.

Nonetheless, you can probably use these devices to mark points of interest (e.g, tile blowouts) or draw 'travel routes' around fairly large problem areas, and use the same device to return to the problem area at a later time.

Bottom Line: The real message of this article on 'high-tech' crop scouting gadgets is that growers should take the opportunity afforded them by the recent spate of 'toad-stranglers' and 'goose-drownders' to document the extent and position of problem areas in their fields caused by the lengthy periods of soggy soils and warm temperatures.

Given that we are in mid-summer, documenting these areas may be easier to do in soybean fields than corn due to soybean plants being shorter and easier to walk to spot problem areas. This information could be useful in the future for making decisions about tile drainage installation or repair, improvements in surface drainage, ameliorating significant soil compaction layers or whether to continue farming that 'wet hole'.

[In deference to Purdue's lawyers, none of the commercial products or services mentioned or linked to in this article are endorsed by me or Purdue University.]

Corn Growers GuidebookFor other information about corn, take a look at the Corn Growers Guidebook on the World Wide Web at

It is the policy of the Purdue Agronomy Department that all persons shall have equal opportunity and access to its programs and facilities without regard to race, color, sex, religion, national origin, age, or disability. Purdue University is an Affirmative Action employer. This material may be available in alternative formats.
© 2000, Purdue University
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