Yadav Sapkota

Date of Graduation

2017

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Energy Land Mangement

Committee Chair

Louis M McDonald

Committee Co-Chair

Thomas Basden

Committee Member

Thomas C Griggs

Abstract

Phosphorus (P) runoff from agricultural fields is a major cause of water quality degradation problems. A P mass balance across the farm could maintain profitability and sustainability of animal-based farms and minimize water quality problems. Comprehensive Nutrient Management Plans (CNMPs) require mineral composition, especially P, data on soil, forage, and manure samples for accurate planning. However, traditional wet chemical methods of P determination are costly, time-consuming, and generate hazardous waste. X-ray fluorescence (XRF) could overcome many of these disadvantages and allow rapid determination of P concentrations. Portable XRF (PXRF) units are Energy Dispersive (ED) systems with low power X-ray tubes (10-40W) in comparison to benchtop units (50-300W). They are light and convenient to use either in benchtop or field-analysis modes. When a sample is scanned, the resulting spectrum identifies the element (peak position or energy); area under the peak (intensity) is proportional to concentration. A few studies have indicated the possible use of PXRF for the analysis of plant tissue and compost samples. However, there is a lack of information for analysis of heterogeneous forage and manure samples, including optimal sample preparation (particle size and moisture content) and instrumental parameters (scan time). The objective of this study was to evaluate the effect of manure moisture content and forage particle size on elemental concentrations determination using PXRF in benchtop mode. Manure samples (n=40) were oven dried at 50 and ground to 0.5 mm size and adjusted to four gravimetric moisture ranges: 10-20%, 20-30%, 40-50%, and 60-70%. Dry hay samples (n=42) were oven dried (600C for 3 days) and ground into two particle sizes (0.25-0.5 mm and 1-2 mm). Prepared samples were scanned by PXRF using a vacuum (<10 torr) and without a filter. Samples were placed in a sample cup over a thin proline X-ray film and scanned for 180s. Some forage samples (n=29) were also scanned for 60s and 120s for scan time analysis. Spectra for each analysis, photon counts (intensity) and P concentration were collected using the S1PXRF software. Reference standards were prepared by microwave digesting forage and manure samples in triplicate followed by elemental quantification through Inductively Coupled Plasma Optical Emission Spectrometry (ICP). Regression analysis, two sample t-test, matched paired t-test, and repeated measures ANOVA were used for data analysis. ICP measured P, K, Ca, Mg, Fe and Cu were in close agreement with West Virginia Department of Agriculture-measured concentration in manure samples. Dried and ground manure samples produced a stronger relationship with ICP-determined P, K, Ca, Fe, Cu, Zn (r 2> 0.90) and Mg (r2=0.59). Presence of moisture negatively affected elemental determination in manure samples. The strength of the relationship decreased with increasing moisture content beyond 20%.;Comparison of PXRF concentration with ICP-determined value indicated that forage P, K, Ca, and Fe (r2>0.88) could potentially be determined with portable XRF. The strength of the relationship increased with decreasing particle size in forage samples. The particle size of the sample was significant while the scan time and the interaction between scan time and particle size were not significant. There was no significant difference between ICP and PXRF measured concentration for 0.25-0.5 mm sample but significant difference between ICP and PXRF concentration for 1-2 mm samples. Likewise, there was a significant difference (p<0.001) between PXRF concentration measured with the two particle size of the sample. Use of different scanning time (60s, 120s, and 180s) did not affect the relationship with ICP concentration for the samples of particle size. Thus, P, K, Ca, Fe, Cu and Zn can be accurately be measured in manure samples and P, K, Ca, and Fe in forage samples using PXRF in benchtop mode. Additional work is needed to extend this to in-field analysis. This simplification of the elemental analytical method could expedite CNMP planning process and contribute to better whole-farm P management.

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