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Title: NEAR-INFRARED REFLECTANCE SPECTROSCOPY FOR THE ANALYSIS OF LOW ORGANIC MATTER 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: 5/19/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Near-infrared reflectance spectroscopy (NIRS) is an instrumental technique using light invisible to the human eye to determine the composition of materials, i.e., forages, grains, foods, etc. The objective of this study was to investigate the potential usefulness of NIRS in determining various constituents [total nitrogen and carbon, several forms of biological active nitrogen (active, biomass and mineralizable), and pH] and parameters [soil source, depth from which sample was obtained, type of tillage used and rate of application of ammonium nitrate fertilizer] of low organic matter soils (LOMS). Soil samples (N = 179) were obtained from experimental plots consisting of two locations with 3 replicate plots under conventional and no till practices at each location with 3 rates of ammonium nitrate for each plot. For each of these, samples were taken from 5 depths for a total of 180 samples (one sample lost). Investigations demonstrated that NIRS can be successfully used to determine some compositional parameters of LOMS (particularly total carbon and nitrogen). It is also apparent that for non-biological parameters (excluding soil type as reflected by source and perhaps pH), that NIRS is not very useful unless a very limited set of samples is used (i.e., single tillage and location). For other determinations, such as the measures of biologically active nitrogen (excluding mineralizable N for which NIRS was totally unsatisfactory), the results were more variable and may be useful depending on the exact needs in question.

Technical Abstract: The objective of this work was to investigate the usefulness of NIRS in determining various constituents (total N and total C, active N, biomass and mineralizable N, and pH) and parameters (soil source, depth from which sample was obtained, type of tillage used and rate of application of NH4NO3 fertilizer) of low organic matter soils. Samples (N = 179) were obtained from experimental plots consisting of two locations with 3 replicate plots under plow and no till practices at each location with 3 rates of NH4NO3 for each plot (2 x 3 x 2 x 3). For each of these, samples were taken from 5 depths for a total of 2 x 3 x 2 x 3 x 5 or 180 samples (one sample lost). Investigations demonstrated that NIRS can be successfully used to determine some compositional parameters of low organic matter soils (particularly total C and total N). It is also apparent that for non- biological parameters (excluding soil type as reflected by source) such as the depth from which the sample was obtained, the rate of application of NH4NO3 fertilizer and the form of tillage used, that NIRS is not very useful, unless a very limited set of samples is used (i.e., single tillage and location). For other determinations, such as pH, biomass N and active N, the results were more variable and may be useful depending on the exact needs in question. Finally, from the results presented here, NIRS is unacceptable for determining soil N mineralizable in 21 days.