No-tillers wanting to get a better handle on how efficiently they’re using nitrogen on corn acres should consider late-season corn-stalk nitrate sampling programs, including one offered by the Iowa Soybean Association On-Farm Network.
For the past decade, the Iowa-based research organization has, through its “Guided Stalk Sampling” (GSS) program, been combining color aerial imagery with late-season, stalk-nitrate testing to help farmers improve nitrogen management on corn ground.
Stalk testing is “guided” by the use of geo-referenced color imagery, overlaid with a soils map, in selecting points where stalk samples will be collected.
The ISA On-Farm Network program has helped establish similar programs with farmer groups in Indiana, Minnesota, Missouri, Illinois, Ohio and states with watersheds draining into the Upper Chesapeake Bay. Similar programs are run in Kansas and Nebraska.
Color aerial imagery shows where nitrogen stresses are occurring in fields, and stalk-nitrate samples taken in the field can confirm if those areas have higher or lower nitrate levels, says Tracy Blackmer, former director of research for the ISA On-Farm Network.
Using geo-referenced aerial photos can show nitrogen stress down to a single row.
“Nitrogen stress is usually not uniform in a field, and fields don’t become nitrogen deficient uniformly,” Blackmer says.
In color aerial imagery, areas of a cornfield that appear light-green to yellow are more likely to be low in nitrogen, while darker green areas generally have sufficient or maybe even excess nitrogen available.
Farmers usually begin a GSS program using geo-referenced imagery, overlaid with a…