Use of Near-infrared Spectroscopy for Monitoring and Analysis of Carbon Sequestration in Soil by P.D. Martin, and D.F. Malley PDK Projects, Inc. Winnipeg, Manitoba, Canada

Vision Soil and plant analyses are available when and where they are needed Need for information, rather than analytical cost, to dictate the number and kinds of analyses Analyses promote sound, sustainable environmental and agricultural management

Purpose Introduce Near-infrared Spectroscopy (NIRS) Describe: –Benefits to use of NIRS –How NIR can be used for soil carbon assessment –Services available from PDK

NIR Facts NIRS provides rapid, chemical-free, flexible analysis NIRS is used globally for food and feed analysis NIRS has enormous potential for agro- environmental applications, including soil carbon assessment

Near-infrared Spectroscopy Utilizes the absorbance of NIR light ( nm) by vibrating bonds between atoms in molecules O-H, C-H, C-N, C-O, P-O, S-O Molecular spectroscopy - analyzes intact samples NIR absorbances obey the Beer/Lambert law

The Work of Doing NIR Analysis Compositional information on samples (n ~>100) is correlated with the spectral information to develop statistical calibration models The calibrations “train” the instrument to analyze future unknown samples

Features does not destroy the sample is rapid, < 2 min/test analyzes many constituents simultaneously analyzes compositional and functional properties field portable

Lab and Field Instrument: Zeiss Corona

Organic Matter Compositional Parameters Organic matter/organic C –% OM, % OC –Total C (LECO) –%C HUMUS –Humic acid fractions –Humic and Fulvic –Fulvic acid fractions –Lignin content –Cellulose content r Performance good – exc. v.good - exc. v.good poor good

Compositional Parameters cont’d r 2 performance % Clay good Total N good - v.good % moisture v.good – exc. 0.9 v.goodCEC 0.9 v.good

Organic Carbon Miniota area Newdale Soil Assoc. Dried, ground samples (2mm) N = nm r 2 = 0.78 SEP = 0.33 %

“Field-moist” applications Moisture corrected calibration and 1.5 MPa moisture tension r 2 = 0.89 SEP = 0.23 % Range = 0.45 – 3.16 % OC Sudduth, K.A. and J.W. Hummel (1993). Soil organic matter, CEC and moisture sensing with a portable NIR spectrophotometer. Trans of the ASAE 36:

Example of On-site Soil Testing Method Soil cores - grid or stratified sampling Cores sliced on-site Presentation of static, “as is”, field moist samples Multiple constituents simultaneously

NIRS Benefits COST ! –LECO OC = $27/sample –NIR OC = $6/sample Minimal sample preparation –Dried and ground (2mm mesh) –Potential for “as is” or “field moist” determinations Timeliness –Potential for immediate analysis

NIRS Benefits, cont. Precision –Precision of NIR equal or better than reference Does not destroy the sample –The same sample can be analyzed many times over –Positive implications for long term and/or incubative studies

NIRS Limitations Site to Site Bias –Potential for bias in predictions of samples from one site using calibrations derived from samples from another site. –Affects absolute accuracy –Does not affect precision This can be corrected by “incorporating” a small number of samples from the “new” site into the calibration. At present, this means that NIRS is not practical for small sample groups

How can NIRS work for you? Objective sample selection 1 –NIRS can be used to select sample sets from a large group of samples which: Retain a maximum representation of overall sample population variability –Samples selected better than random because: Greater recovery of range Higher variance Better Kurtosis (more even distribution) 1 Stenberg, B. et al. (1995) Use of near infrared reflectance spectra of soils for objective selection of samples. Soil Science. 159:

Objective Sample Selection, cont. Using NIR for selecting analytical samples reduces cost directly by lowering the number of samples that need to be analyzed to encompass soil variability. –Stenberg, et al. estimated a 70% reduction in cost for their study using this method –For their study, the overall n = 144 samples, selected n = 20 samples

Calibration and Prediction Calibrations are developed on a selected set of samples (ie. using the NIR selection method) These calibrations can be used to predict the remaining samples. –Requires large sample sets –n calibration :100 samples recommended

Calibration and Prediction, cont. Extra cost of calibration and accompanying wet chemistry is offset by a large economy of scale –Once a calibration is developed, it only requires updating with a much smaller number of QA/QC samples Calibrations will eventually exist for various soils, bringing initial costs down

Monitoring and Long-term Soil Quality Assessment NIR spectra contain information for both carbon quantity, and carbon quality in soil High precision plus lower cost of NIR results make large scale assessments of soil carbon flux much more feasible, both: –Over time –Under varying management practices.

Monitoring and Long-term Soil Quality Assessment, cont. Non destructive nature of NIR, coupled with “as-is” and/or “on-site” assessment potential mean that: –The same sample could be analyzed indefinitely over time. –Could reduce potential subsampling error –Could increase relevance of results

Sensing Soil Quality Large Area Surveillance of Soil Condition and Trend

Services Available from PDK Introductory Pricing Objective Sample Selection Samples submitted dried and ground (2mm) –$6.00 per sample

Services Available from PDK, cont. Compositional Analysis 1.Calibration Samples (100+ samples, 5 g/sample min) submitted dried and ground in borosilicate vials or bags Reference values submitted for constituents of interest, including QA/QC data from the analytical laboratory. (Reference chemistry can be arranged at a Lab of your choice, at commercial rates -extra) –First calibration: $6.00/sample plus $150 –Each additional calibration: $250

Compositional Analysis, cont. 2. Prediction of future samples Prediction of future unknown samples of the same type as in the calibrations, submitted dried and ground –First constituent: $6.00/sample –Each additional constituent: $1.00/sample

Services available from PDK, cont. Consulting –Custom Quote for: Setup of personal NIR program Setup of field portable instrument Contract Research Instrument selection/evaluation

Conclusions NIR is the only practical method for analyzing large numbers of samples for measurement of C stores NIR has potential to determine quality/persistence of organic C in soil

Acknowledgments Foss NIRSystems Inc., USA Carl Zeiss, Germany Agriculture and Agri-Food Canada Manitoba Rural Adaptation Council (MRAC) Industrial Research Assistance Program (IRAP)