A team ofIowa State University scientists have measured nitrate in soil with a uniqueinfrared sensor systemopening the possibility of determining the level of thisvital nutrient in real time as fertilizer is being applied to fields.

“We were actuallysurprised that we could get in the parts per million range with the soil movingpast the analyzer,” said JohnMcClelland, a research scientist with theRoyJ. Carver Department of Biochemistry, Biophysics and Molecular Biologyand AmesLaboratory-U.S. Department of Energy.

The team used atechnology, invented at Ames Laboratory, called transient infrared spectroscopy(TIRS) to measure nitrate insoil and then compared those values to onesobtained using traditional soil testing. TIRS works by measuring lightemissions inthe infrared spectrum after hot air is applied to the surface ofthe moving soil. The research was published in the journalAppliedSpectroscopy.

The research teamstressed that this was a preliminary study in the lab and many steps arenecessary before a possiblecommercial tester could be available.

“There are a lot ofsteps up that ladder before we’d have any hope of commercialization. Thebreakthrough here is that no onehas been able to come up with a plausible toolfor effectively measuring nitrate in the field,” said David Laird, a professorofagronomy.

He and McClelland didthe work with Roger Jones, a research scientist with the Roy J. CarverDepartment of Biochemistry,Biophysics and Molecular Biology and AmesLaboratory-USDOE and Sam Rathke, an agronomy research associate.

Laird emphasized thatnitrate was measured as opposed to total nitrogen. He said nitrate measurementis especially importantbecause it is the dominant available form of nitrogenfor growing crops, but is very mobile in the soil.

“Agricultural soils inIowa are leaky; that’s why we have so much nitrate going down the Mississippiand contributing to the zoneof hypoxia in the Gulf of Mexico,” he said. “Oneof the best ways to improve nitrogen use efficiency in agricultural productionisto spoon-feed nitrogen to the crop while it is growing. To do this, you needto be able to diagnose what the situation is at thecritical time; does thecrop need more nitrogen or not.”

Some technologiespropose determining nitrogen needs by analyzing the color of the growing crop’scanopy. Laird said thatapproach is complicated by alternative reasons thecanopy could start to yellow or not have the right colors, such as disease orenvironmental conditions.

Another advantage tothis technology is the ability to quickly determine the “spatial variability”of nitrate, in which one part ofthe field may have more than enough nitrogen,and another part of the field may be deficient.

“The late springnitrate test can do that, but it takes an army of people with soil probes togather samples, which then have tobe analyzed in the lab,” said Laird. “If youcould short-circuit all of that using a spectroscopic technique, that allows usin realtime to assess the current status of the soil’s nitrate level, it wouldgreatly benefit precision nitrogen management.”

McClelland said thenext step for the research is to test several soil types to see if they areable to obtain the same quality ofdata, and would help simulate fieldconditions because soil types vary continuously. The initial tests in the labwere on one typeof soil that was placed on a disc that rotated under theanalyzer’s probe.

“If we get good resultson additional soil samples that would be impetus to go on and get funding to goon beyond that,” hesaid.

If the researchprogresses to field tests, McClelland said it should be feasible to design acost effective tool that just looks at thenecessary wavelengths instead of themore expensive test machine they used. He has been in touch with Frenchresearcherswho are working on commercializing a smaller, more compactdetector.

Laird said a fieldmodel also would need an attachment that would remove any plant material fromin front of the probe andopen the soil so that the probe could be viewing afresh patch of soil an inch or two beneath the soil’s surface.