Phosphorus Determination in Forage and Manure Using Portable X-Ray Fluorescence Spectroscopy.

Traditional wet chemical methods of total P determination require destructive sampling, are costly, time-consuming, and generate hazardous waste. X-ray fluorescence (XRF) could overcome many of the disadvantages of wet chemical analysis and allow quick determination of P concentration. Several studies have indicated the possible use of Portable XRF (pXRF) in plant elemental concentration determination; however, there is still a gap in optimal sample preparation (particle size and moisture content) and instrumental parameter (scan time). Dried hay samples (n=42) were collected, oven dried and ground into three particle sizes (1-2mm, 0.25-0.5 mm, and <106um) and analyzed using pXRF and wet chemical method. Comparison of pXRF concentration with ICP (Inductively coupled plasma) determined value indicates that P could potentially be determined with portable XRF. The strength of the relationship increased with decreasing particle size. The coefficient of determination (r²) for 1-2 mm sample was 0.69 (p value = <0.001), for 1-2mm sample was 0.79 (p value = <0.001) and for <106um sample was 0.83 (p value = <0.001). Use of different scanning time (60s, 120s, and 180s) did not affect the relationship with ICP concentration for the samples of all particle size. In addition, dried and ground (0.5 mm) manure samples (n=40) produced r² value of 0.70 (p value= <0.001). The presence of moisture negatively affected P determination in manure samples. The strength of the relationship decreased (r²=0.59 for 40-50% moisture level and r²=0.27 for 60-70% moisture level) with increasing moisture content beyond 20%. Thus, using pXRF, P concentration in dried and ground hay and manure samples can be determined quickly at reduced cost. This, simplification of the P analytical method could contribute to better whole-farm P management.