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Quantifying spatial and temporal fluxes of phosphorus (P) within and among agricultural production systems is critical for sustaining agricultural production while minimizing environmental impacts. To better understand P fluxes in agricultural landscapes, P-FLUX, a detailed and harmonized dataset of P inputs, outputs, and budgets, as well as estimated uncertainties for each P flux and budget, was developed. Data were collected from 24 research sites and 61 production systems through the Longterm Agroecosystem Research (LTAR) network and partner organizations spanning 22 U.S. states and 2 Canadian provinces. The objectives of this paper are to (a) present and provide a description of the P-FLUX dataset, (b) provide summary analyses of the agricultural production systems included in the dataset and the variability in P inputs and outputs across systems, and (c) provide details for accessing the dataset, dataset limitations, and an example of future use. P-FLUX includes information on select site characteristics (area, soil series), crop rotation, P inputs (P application rate, source, timing, placement, P in irrigation water, atmospheric deposition), P outputs (crop removal, hydrologic losses), P budgets (agronomic budget, overall budget), uncertainties associated with each flux and budget, and data sources. Phosphorus fluxes and budgets vary across agricultural production systems and are useful resources to improve P use efficiency and develop management strategies to mitigate environmental impacts of agricultural systems. P-FLUX is available for download through the USDA Ag Data Commons (https://doi.org/10.15482/USDA.ADC/1523365).

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Determination of soil organic carbon (SOC) is highly desirable for assessing fertility and carbon sequestration; however, numerous methods of determination warrant study of method agreement. Recently, a novel method was developed following dichromate oxidation using a microplate spectrophotometer. This novel method was compared with (i) total C by dry combustion-soil inorganic carbon (DC w/o pretreatment-Pcal); (ii) traditional Walkley-Black titration (WBTIT) and (iii) loss on ignition (LOI 360°C) in calcareous soils of south central Idaho (n=75) in conjunction with North American Proficiency Testing program soils (n=10). A two-way ANOVA was fit with soils as a blocking factor to identify any difference between methods, means were separated using Tukey's HSD (α=0.05). Additional comparisons were made for all soils (n=85) and for soils in the lower 75 th percentile of SOC determined by WBTIT (n=56) using regression analysis. Only the WBTIT and LOI 360°C methods were statistically equivalent nevertheless there was high agreement (Lin's concordance coefficients >0.90) between all methods (n=85). Under low SOC soils (n=56) the agreement between all methods decreased, but the WBSPEC method fit other methods comparatively well r 2 = 0.71, 0.74, and 0.78 for LOI 360°C , DC w/o pretreatment-Pcal, and WBTIT respectively. The WBSPEC method provided estimates of SOC between the methods currently used in the region while reducing hazardous waste generation over traditional WBTIT and sample handling over LOI 360°C and DC w/o pretreatment-Pcal methods, positioning it as a sensible option for SOC determination in low SOC calcareous soils of south central Idaho.

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