Abstract
The recent development of portable X-ray fluorescence spectrometers (PXRF) has created new avenues for rapid plant elemental concentration determination at reduced cost while avoiding hazardous chemicals. A few studies have indicated the potential use of PXRF for homogenous plant tissue analysis. However, there is a lack of information for analysis of heterogeneous plant samples like livestock forage, which consists of a mixture of several species and plant parts, each varying in elemental concentration. Our objective was to evaluate PXRF for forage analysis, specifically the effect of forage particle size and scan time on important elements including P, K, Ca, and Fe determination. Hay samples (n = 42) were oven dried (60°C for 3 days) and ground into three particle sizes (≤0.5 mm, 0.25–0.5 mm and 1–2 mm). Prepared samples were scanned by PXRF using a vacuum (<10 torr) without a filter. Samples were placed in cups over thin prolene X-ray film and scanned for 180 s. A subset (n = 29) were also scanned for 60 and 120 s. PXRF counts for P, K, Ca, and Fe were compared with laboratory Inductively Coupled Plasma Optical Emission Spectroscopy (ICP) determinations, using regression models. Results indicated that these elements could potentially be determined with PXRF (r2 ≥ 0.70) in heterogeneous forage samples. Relationship strength increased with decreasing particle size, however, the relationship was still strong (r2 ≥ 0.57) at the largest particle size. Scanning time did not affect the relationship with ICP concentration for any of the particle sizes evaluated. This work demonstrated that with the right sample preparation PXRF can obtain results comparable to acid digestion and ICP regardless of sample composition, and suggests the potential for in situ determinations.
Highlights
Forage is a major ruminant livestock feed and source of minerals including P, K, Ca, Mg, and Fe
Our results indicate that forage samples can be analyzed with as little as 60 s without losing accuracy
Mineral composition data in forage is an important part of the animal feeding plan
Summary
Forage is a major ruminant livestock feed and source of minerals including P, K, Ca, Mg, and Fe. Minerals are often still quantified with expensive and time-consuming wet-chemical methods; acid digestion followed by atomic spectroscopic techniques (Karla, 1998) These provide accurate quantification of minerals, they can have serious shortcomings. Assuming that half of the 20,600 livestock farms in West Virginia (West Virginia Department of Agriculture, 2017) submits 4–8 forage samples annually, the annual cost of forage analysis for mineral determination is 1.2–2.3 million dollars; significantly more nationally. Along with this cost, the generation of hazardous waste is a consideration. X-ray fluorescence (XRF) could overcome many of these disadvantages of wet chemical analysis and allows quick determination of elemental concentrations at reduced cost in plant samples (Reidinger et al, 2012; Towett et al, 2016; McGladdery et al, 2018)
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