A Case study in the use of X-Ray Fluorescense to measure relationship between pH and Calcium levels in the soil.

Richard Stone. NDA. Agriculture. UK

Introduction

In the low rainfall area surroundingCondobolin (100 km radius)

• Soil acidity is seen mostly on the red earths

• In 2000, approximately 57% of the red soils in this area had a pH of less than 5.0

• Of these, 24% have a pH less than 4.5 and 33% have a pH of 4.5 – 5.0

Department Ag NSW

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Series3Number of Observations. Number of Observations % at each pH.

Distribution of surface soil pH in Central Western NSW

Introduction to X-ray Fluorescense (XRF)

XRF Technology is a non –destructive analytical technique used to determine the elemental composition of materials. XRF analyzers determine the chemistry of a sample by measuring the fluorescent (or secondary) X-ray emitted from a sample when it is excited by a primary X-ray source.

The X-ray fluorescence processA solid or a liquid sample is irradiated with high energy X-rays from a controlled X-ray tube.When an atom in the sample is struck with an X-ray of sufficient energy (greater than the atom’s K or L shell binding energy), an electron from one of the atom’s inner orbital shells is dislodged.The atom regains stability, filling the vacancy left in the inner orbital shell with an electron from one of the atom’s higher energy orbital shells.The electron drops to the lower energy state by releasing a fluorescent X-ray. The energy of this X-ray is equal to the specific difference in energy between two quantum states of the electron. The measurement of this energy is the basis of XRF analysis.

Interpretation of XRF spectra• Interpretation of XRF spectra• Most atoms have several electron

orbitals (K shell, L shell, M shell, for example). When x-ray energy causes electrons to transfer in and out of these shell levels, XRF peaks with varying intensities are created and will be present in the spectrum, a graphical representation of X-ray intensity peaks as a function of energy peaks. The peak energy identifies the element, and the peak height/intensity is generally indicative of its concentration.

Case Study of 29 paddocks South West of Nyngan NSW

• 29 paddocks ( 7,000 hectares) of red earth dry land farming country was sampled and tested using the CSBP laboratories in West Australia. Calcium and pH levels were recorded and calcium levels tested using XRF. As can be seen by the results ( next slide) there is a strong correlation between Calcium and pH

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XRF cALCIUM/PH RELATIONSHIP 29 paddocks at nyngan nsw

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Results