Soil nutrients affect crop growth and yield. Growth depends on soil
phosphorus, potassium and nitrogen availability and has an impact
on soil productivity. Most soils have an inadequate supply of
phosphorus. Chemical fertilizers and manure are most often added to
boost soil phosphorus. There are two reasons to adopt technologies
that can result in precision fertilizer application: phosphorus
fertilizers are constrained by finite resources—therefore accurate
application and efficient use is required. Second, over fertilization  
can result in runoff and leaching into water systems. This can lead to
contamination and eutrophication of inland fresh water bodies and
stimulation of phytoplankton and microalgae growth in coastal water
bodies. This can lead to the decline of light penetration and
dissolved oxygen.

Conventional analysis of soil phosphorus is laborious and time-
consuming. NIR spectroscopy provides an alternative that is fast,
less costly and can be applied in situ. In soil, phosphorus usually
takes the form of phosphates: calcium phosphate, aluminum
phosphate, iron phosphate dihydrate and magnesium phosphate
hydrate. Iron phosphate dihydrate has recognizable absorbance
peaks at 867, 1464 and 1944nm. Magnesium phosphate hydrate has
two peak values at 1419 and 1938nm. Calcium phosphate shows two
distinct peaks at 1439 and 1948nm. Aluminum phosphate shows low
absorbance between 1374 and 2500nm.

PSR+ is a lightweight, reliable high resolution NIR
spectroradiometer designed for field use. The PSR+ covers the full
UV/VIS/NIR range from 350-2500 nanometers with unmatched
sensitivity and accuracy. It is easy for one person in the field to use
with an optional handheld microcomputer and direct screw-on
lenses, or fiberoptic connection to a pistol grip or sample contact
probe. The PSR+ includes our exclusive DARWin SP Data Acquisition
software with access to the USGS spectral library and 19 vegetation
indices. It can work in standalone mode to store up to 1000 field
scans before offloading. It is supplied with two rechargeable lithium-
ion batteries each capable of up to 4 hours of use for a total of 8
hours of scanning. The PSR+ is also available with a benchtop probe
and sample compactor for soil analysis use in the lab.

Or take ultra-high resolution measurements with the
spectroradiometer.  Resolution at FWHM for the SR6500 is:
•        1.5nm @ 700nm
•        3.0nm @ 1500nm
•        3.8nm @ 2100nm

Resolution is achieved using three high density solid state
thermoelectrically cooled photodiode arrays.

The SR-6500 features the following Noise Equivalence Radiance
(NER) performance with a 1.5 meter fiber optic:
•        1.0 x 10-9 W/cm2/nm/sr @ 400nm
•        2.8 x 10-9 W/cm2/nm/sr @ 1500nm
•        6.8 x 10-9 W/cm2/nm/sr @ 2100nm

NER is a measure of instrument sensitivity. Other features of the SR-
6500 include:
•        All fixed optics – no moving parts for rugged reliability
•        Auto-exposure, auto dark current shutter
•        DARWin SP Data Acquisition software saves all scans as
     ASCII files for use with other software programs

For field work, the SR-6500 can be placed in a backpack. It runs off
one lithium-ion battery. Two are provided for up to 6 hours of in-field

Optional EZ-ID sample identification software includes access to
mineral identification libraries — very useful for identifying clays in
soil. Using pattern matching algorithms, EZ-ID matches your target
scan to known samples and provides a matching “confidence level”
percentage. It also allows you to quickly take scans of known
samples and create your own region-specific soils library.

Since DARWin software saves all your spectra as ASCII files, it can
easily be imported into 3rd party analysis or chemometric programs
like TSG, Camo’s Unscrambler and R2.

In addition to measuring phosphorus content, other soil analysis
applications can include: nitrogen measurement, topsoil fertility,
erosion risk, hydraulic properties,  soil degradation,  total organic
carbon, organic matter in soil, CEC, and indirect measurement of soil
 First in Full Range PDA Spectrometer, Spectroradiometer and Spectrophotometer Systems
Every Spectral Evolution instrument includes
DARWin SP Data Acquisition software.
Scans can be compared using multiple
scans in a single plot.
Measuring phosphorus in soil
 First in Full Range PDA Spectrometer, Spectroradiometer and Spectrophotometer Systems
1 Canal Street  ◊  Unit B1
Lawrence, MA 01840  USA
Tel: 978 687-1833  ◊  Fax: 978 945-0372

Copyright © 2012 Spectral Evolution, Inc
The benchtop probe includes a sample compactor for powders and soils. Soil analysis can also be done in
the field with our 10mm or 3mm spot size contact probes.
PSR+ works with our benchtop probe and compactor for in the lab soil analysis.