ICRAF Spectral Library

The ICRAF spectral library contains over 30,000 spectra (wavelength range of 350 to 2500 nm) of more than 12,000 soil samples, 168 sediment samples, 500 plant samples, and several manmade material samples and rock samples. Matching attribute data on physical and chemical properties are available for large numbers of soil and plant samples.  Samples from more than 3000 sites in the Kenya Lake Victoria Basin are georeferenced to survey grade accuracy. More specialized attribute data, not yet documented in the main database, are available for specific sets of samples. The library provides a valuable resource for testing new analytical approaches in soil spectroscopy and remote sensing applications.

Soil Library
Organic Resource Library
Database Structure
Spectral methods

 

Soil Library

The soil samples are mostly from Kenya, but including samples from other countries in eastern and southern Africa and Indonesia. The samples were taken from ICRAF multi-location experiments, on-farm trials, and soil surveys conducted from 1993 to present. Basic soil properties analyzed by the ICRAF soil laboratory are available for over 1000 soils (see below). The library includes soils from Malawi, Kenya, Rwanda, Tanzania, Uganda, Zambia, and Zimbabwe, taken from a wide variety of landscape positions, parent materials, and land uses. Although the soils were not formally classified on-site they were sampled from areas broadly mapped (1:1 million) as Soil Taxonomy orders Alfisols, Andisols, Aridisols, Entisols, Histosols, Inceptisols, Mollisols, Oxisols, Ultisols and Vertisols. 

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Organic Resource Library

The plant samples include samples from the Organic Resource Database System (TSBF - Imperial College Wye)

Plant properties in the ICRAF Spectral Library

Property

n

Min

Max

N

319

0.13

6.6

N

514

0.13

6.6

P

351

0.01

1.2

K

306

0.04

6.6

Ca

229

0.01

6.9

Mg

220

0.02

2.4

Lignin

319

1.9

44

Soluble polyphenols

319

0.01

15

† Samples for which lignin and polyphenol were also determined.
‡ All samples for which N was determined.

 

Database Structure

The data is stored in a Microsoft Access database. The data tables and fields in the ICRAF Spectral Library Database are specified below.

Table

Column

Fieldname

Description

Soil Lab Data

1

Batch

Batch number that a soil or plant sample is allocated to by the ICRAF Soil Laboratory.

Soil Lab Data

2

Labid

Laboratory ID code allocated to a soil or plant sample by the ICRAF Soil Laboratory. Both the Batch and Labid are required to uniquely identify a sample. This combination of codes is used to match soil and plant analytical data produced by the laboratory with the reflectance spectra.

Soil Lab Data

3

ph

Soil pH. 1:2.5 soil:solution ratio.

Soil Lab Data

4

exa

Exchangeable acidity (cmolc kg-1). Extraction with 1M KCl using a 1:10 soil:solution ratio, analyzed by NaOH titration. Samples with pH>=5.5 were assumed to have zero exchangeable acidity.

Soil Lab Data

5

exca

Exchangeable Ca (cmolc kg-1). Extraction with 1M KCl using a 1:10 soil:solution ratio, analyzed by atomic absorption spectrometry.

Soil Lab Data

6

exmg

Exchangeable Mg (cmolc kg-1). Extraction with 1M KCl using a 1:10 soil:solution ratio, analyzed by atomic absorption spectrometry.

Soil Lab Data

7

exna

Exchangeable Na (cmolc kg-1). Extraction with 1M KCl using a 1:10 soil:solution ratio, analyzed by flame photometry. Samples with pH <7.5 were assumed to have zero exchangeable Na.

Soil Lab Data

8

exk

Exchangeable K (cmolc kg-1). Extraction with 0.5M NaHCO3 + 0.01M EDTA (pH 8.5, modified Olsen) using a 1:10 soil:solution ratio and analyzed by flame photometer.

Soil Lab Data

9

exp

Exchangeable P (mg kg-1). Extraction with 0.5M NaHCO3 + 0.01M EDTA (pH 8.5, modified Olsen) using a 1:10 soil:solution ratio and analyzed colorimetrically (molybdenum blue).

Soil Lab Data

10

soc

Organic C (g kg-1). Determined colorimetrically after H2SO4–dichromate oxidation at 150°C.

Soil Lab Data

11

clay

Clay content (g kg-1). Particle size distribution was determined using the hydrometer method after pre-treatment with H2O2 to remove organic matter

Soil Lab Data

12

sand

Sand content (g kg-1). Particle size distribution was determined using the hydrometer method after pre-treatment with H2O2 to remove organic matter

Soil Lab Data

13

silt

Silt content (g kg-1). Particle size distribution was determined using the hydrometer method after pre-treatment with H2O2 to remove organic matter

Soil Lab Data

14

amn

N mineralization potential (mg kg-1 d-1) was determined by determination of ammonium production with 7-d anaerobic incubations at 40°C

Soil Lab Data

15

exbas

Exchangeable bases (cmolc kg-1.) Calculated as the sum of exchangeable Ca, Mg, Na, and K,

Soil Lab Data

16

ecec

Effective cation exchange capacity (cmolc kg-1.) Calculated as the sum of exchangeable acidity and exchangeable bases.

Soil Lab Data

17

ececlay

Effective cation exchange capacity per unit clay (cmolc kg-1 clay) calculated as effective cation exchange capacity divided by the clay fraction.

Spectral Codes

1

Study

Code denoting the research study with which the spectra are associated. See "Studies" table for description of study codes.

Spectral Codes

2

Batch

Batch number that a soil or plant sample is allocated to by the ICRAF Soil Laboratory.

Spectral Codes

3

Labid

Laboratory ID code allocated to a soil or plant sample by the ICRAF Soil Laboratory. Both the Batch and Labid are required to uniquely identify a sample. This combination of codes is used to match soil and plant analytical data produced by the laboratory with the reflectance spectra.

Spectral Codes

4

Material

Material type scanned. Soil = soil samples; Sediment = sediment samples; Plant = plant samples; Rock = rock or mineral samples; Manmade = manmade samples; S_Card = internal standard (brown coloured card); S_Mylar = internal standard (Mylar two-way reflectance); S_Soil = internal soil standard 1; S_Soil2 = internal soil standard 2. [Further details of materials are described in the Treatment field]

Spectral Codes

5

Spectrum#

Spectrum code given when saving the original spectra on the spectrometer. It is used for matching the Spectral Data to the Spectral Codes tables.

Spectral Codes

6

Spectralon

White reference code issued by Labsphere for calibrated Spectralon. This code can be used to match spectra with the white reference calibration spectrum to correct relative reflectance to US National Laboratory Traceable Standard SRS-99-020-M99 (MIST).

Spectral Codes

7

Site

Name of geographic location of sample.

Spectral Codes

8

Plot_Code

Plot code used for matching samples to georeferencing and other field data in landscape level studies.

Spectral Codes

9

Gradsect

Gradient-directed transect number (generally directed down steepest slope) used in landscape level studies.

Spectral Codes

10

Position

Position (in metres) of exact sample location within a plot or gradsect (generally directed down steepest slope from plot edge or start of transect).

Spectral Codes

11

Plot

Plot code used in field experiments (study specific).

Spectral Codes

12

Block

Block code used in field experiments (study specific).

Spectral Codes

13

Treatment

Treatment code used in field experiments (study specific) or sample description.

Spectral Codes

14

Depth Code

Sequential numbering of soil depth layers sampled from surface layer downwards (study specific).

Spectral Codes

15

Depth

Soil depth range sampled (metres).

Spectral Codes

16

Replicate

Replicate number for dishes of the same material sample scanned by the spectrometer.

Spectral Codes

17

Rotation

Rotation number where the same dish of the same sample is scanned by the spectrometer, rotated through 90 degrees on each successive rotation.

Spectral Codes

18

Region

ICRAF region from which sample was collected (Eastern Africa, Southern Africa, Western Africa, SE Asia, Latin America).

Spectral Codes

19

Country

Country from which sample was collected.

Spectral Codes

20

Optics

Optical set up used for reflectance readings. Lamp = raw fibreoptic from above illuminated with Lowell lamps (Shepherd & Walsh, 2000);  torch =  viewed from below using a high intensity reflectance probe, through Duran glass petri dishes; torch_B = torch plus black background plate; mug = viewed from below using a high intensity source probe, through Duran glass petri dishes; mug_B = mug probe plus black background plate; outdoors = solar illumination

Spectral Codes

21

Calibration

Instrument calibration number issued by Analytical Spectral Devices after each recalibration/service.

Spectral Data

1

Spectrum#

Spectrum code given when saving the original spectra on the spectrometer. It is used for matching the Spectral Data to the Spectral Codes tables.

Spectral Data

2

W350_W2500

Relative reflectance in each waveband from 350 nm to 2500 nm at 10 nm intervals (216 wavebands).

 

Spectral Methods

Samples were scanned using a FieldSpecTM FR spectroradiometer (Analytical Spectral Devices Inc, Boulder, Colorado) at wavelengths from 0.35 to 2.5 µm with a spectral sampling interval of 1 nm. The optical set up used for a particular sample is recorded in the database, and the methods are described on the Sensing Soil Quality Page and Reflectance Measurements Page. The relative reflectance spectra in the database were resampled to a spectral interval of 10 nm, by selecting every tenth–nanometer value from 0.35 to 2.5 µm, to reduce the volume of data for analysis and to match it more closely to the spectral resolution of the instrument (3 to 10 nm). The original spectra at a 1 nm sampling interval are available in a data archive.