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 (a) total C by dry combustion − soil inorganic carbon (DC _{w/o pretreatment} –pressure calcimater [Pcal]); (b) traditional Walkley–Black titration (WBTIT) and (c) 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 honestly significant difference test (α = .05). Additional comparisons were made for all soils ( n = 85) and for soils in the lower 75th 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 > .90) between all methods ( n = 85). Under low SOC soils ( n = 56) the agreement between all methods decreased, but the Walkley–Black spectrophotometric method (WBSPEC) method fit other methods comparatively well r ²  = .71, .74, and .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.

Insufficient characterization of soil organic carbon (SOC) dynamics in semi-arid climates contributes uncertainty to SOC sequestration estimates. This study estimated changes in SOC (0–30 cm depth) due to variations in manure management, tillage regime, winter cover crop, and crop rotation in southern Idaho (USA). Empirical data were used to drive the Denitrification Decomposition (DNDC) model in a “default” and calibrated capacity and forecast SOC levels until 2050. Empirical data indicates: (i) no effect (p = 0.51) of winter triticale on SOC after 3 years; (ii) SOC accumulation (0.6 ± 0.5 Mg ha^–1 year^–1) under a rotation of corn-barley-alfalfa^x3 and no change (p = 0.905) in a rotation of wheat-potato-barley-sugarbeet; (iii) manure applied annually at rate 1X is not significantly different (p = 0.75) from biennial application at rate 2X; and (iv) no significant effect of manure application timing (p = 0.41, fall vs. spring). The DNDC model simulated empirical SOC and biomass C measurements adequately in a default capacity, yet specific issues were encountered. By 2050, model forecasting suggested: (i) triticale cover resulted in SOC accrual (0.05–0.27 Mg ha^–1 year^–1); (ii) when manure is applied, conventional tillage regimes are favored; and (iii) manure applied treatments accrue SOC suggesting a quadratic relationship (all R² > 0.85 and all p < 0.0001), yet saturation behavior was not realized when extending the simulation to 2100. It is possible that under very large C inputs that C sequestration is favored by DNDC which may influence “NetZero” C initiatives.

Surface broadcast of dairy slurry is a common practice; however, concerns over nuisance odors and nutrient losses have prompted research into alternatives. Manure injection is one practice that addresses these concerns but is not widely adopted. Therefore, two studies were conducted to quantify NH3-N loss by volatilization, impacts on soil N cycling, and microbial response between surface broadcast and subsurface injection of dairy slurry. A constant air flow volatilization chamber system measured NH3-N losses and soil inorganic N, mineralizable carbon, and active microbial biomass. A 40-day static air incubation was performed to study nitrogen transformations over a longer period after application. Statistical significance was evaluated at the α = 0.05 level. In the volatilization study, subsurface injection reduced NH3-N losses by 98% and 87% in a clay loam and sandy loam, respectively, resulting in greater soil inorganic nitrogen compared with surface application. There were no significant differences in active microbial biomass between treatments. Surface application prompted greater microbial respiration in the sandy loam, but there were no significant differences between treatments in the clay loam. In the static incubation study, differences in soil NO3−-N became significant on day 28, and by day 40, injection showed increases in soil NO3−-N of 13% and 26% in the sandy loam and clay loam, respectively, relative to surface application. While the effect of subsurface injection on soil microbial response was unclear, it remains a tool that can greatly reduce NH3-N losses by volatilization and increase soil plant available nitrogen.

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 Long‐term 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).

Access to livestock manure is increasing in semi‐arid cropping systems of U.S. Northwest prompting evaluation of fertilization strategies on regional production systems. A study conducted from fall 2012 to 2019 used: fall‐ or spring‐applied dairy manure (56 Mg ha⁻¹), fall‐applied composted dairy manure (33 Mg ha⁻¹), spring‐applied urea or SUPERU (Koch Agronomic Services), and a control (n = 6) on a corn (Zea mays L.)–barley (Hordeum vulgare L.)–alfalfa (Medicago sativa L.)–alfalfa–alfalfa rotation. The effects of fertilization strategies on (a) soil nutrients, (b) crop tissue nutrient concentration and removal, and (c) digestibility and energy content of forages are discussed. Compost and manure additions increased corn silage N, P, K, respectively, by 0.86, 0.28, and 2.4 g kg⁻¹ over other treatments; silage Ca and Mg were depressed 0.4 and 0.53 g kg⁻¹ by manure applications. Barley grain P_removal and K_removal increased 5.10 and 7.65 g kg⁻¹ under manure applications relative to urea and SUPERU treatments while crude protein (CP) (19.1 g N kg⁻¹) neared limits of high‐quality malt extract (16–19 g N kg⁻¹). Compost and manure increased alfalfa K by 2.3 and 5.5 g kg⁻¹ over other treatments, approaching levels of concern for hypocalcemia in dairy cattle (≥30 g K kg⁻¹). No major impact on corn silage or alfalfa quality parameters, were observed. Present Idaho nutrient removal estimates were representative of corn and alfalfa, but not barley in which observed N removal was 28% lower. In 17 of 18 instances, contrast testing suggested nutrient removal differed under organic amended treatments, suggesting nutrient removal modifiers in production systems receiving organic amendment may need established.