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Title: NEAR-INFRARED REFLECTANCE SPECTROSCOPY FOR THE DETERMINATION OF BIOLOGICAL ACTIVITY IN AGRICULTURAL SOILS

Author
item Reeves Iii, James
item McCarty, Gregory
item Meisinger, John

Submitted to: Near Infrared Spectroscopy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Near-infrared reflectance spectroscopy is an instrumental technique which uses light to determine the composition of organic materials. The determination of the biological potential of soils to convert organic nitrogen into forms useable by plants is important if accurate estimates of the available nitrogen in manures are to be made. The objective of this work was to investigate the usefulness of NIRS in determining biological activity in agricultural soils. One hundred and seventy-nine samples obtained from experimental plots were studied. Biological activity as measured by four enzymes and nitrification potential (NP) was determined by conventional methods and NIRS. Investigations showed NIRS to be capable of determining biological activity as reflected by the four enzymes and NP to at least some degree. The results, while positive, were not as good as found previously for many other components (i.e., total carbon and nitrogen). Efforts at discrimination into high, medium, and low activities were not successful, and for the most part, results based on subsets, i.e., samples from only one location, were not found to be an improvement. Correlation analysis indicated that measures of biologically active nitrogen may be the basis for these determinations. In conclusion, the results indicated that NIRS may be useful for the rapid determination of soil biological activity in cases where extreme accuracy is not required or not practical.

Technical Abstract: The objective of this work was to investigate the usefulness of near-infrared reflectance spectroscopy (NIRS) in determining biological activity in agricultural soils. A FOSS-NIRSystems model 6500 spectrometer, equipped with a spinning sample cup module, was used to scan 179 soil samples obtained from experimental plots at two locations with three replicate plots under plow and no-till practices at each location with three rates of NH4NO3 for each plot with samples taken from five depths for a total of 180 samples (one sample lost). Biological activity as measured by four enzymes (dehydogenase, phosphatase, arylsulfatase and urease) and nitrification potential (NP) was determined by conventional methods and NIRS. Investigations showed NIRS to be capable of determining biological activity as reflected by the four enzymes and NP to at least some degree. With the best R2 in the range of 0.8, the results, while positive, were not as good as found previously for many other components (i.e., total C and N). Efforts at discrimination into high, medium, and low activities were not successful, and for the most part, calibrations based on subsets, i.e., samples from only one location, were not found to be an improvement. Correlation analysis indicated that measures of biologically active nitrogen may be the basis for these determinations. The results indicated that NIRS may be useful for the rapid determination of such activity in cases where extreme accuracy is not required.