Reliable estimates of N excretion in the urine and feces of beef cattle are essential for developing cost-effective and environmentally sound nutrient management plans. A meta-analysis dataset was compiled that included data for starting live BW, DMI, N intake, dietary CP and RDP concentrations, urine N excretion, and feces N excretion. The data were taken from 12 individual feeding trials that included N balance data, and represented a total of 47 different dietary treatments and 255 animals. Correlation analysis was used to determine the animal and dietary parameters that were most closely related to N excretion in urine and feces by beef cattle. A multivariate mixed modeling approach was used to develop empirical equations to predict excretion of urine N, feces N, and the partitioning of total N excretion between urine and feces, as a function of N intake and the concentration of dietary CP. Univariate, regression, and mean difference comparisons indicated 46 to 95% agreement between observed and predicted values for the developed equations. Evaluation of the equations with an independent dataset taken from 6 studies, and 2 random subsets of the meta-analysis dataset showed moderate agreement (P < 0.05, r(2) = 0.34 to 0.86) for urine N excretion as a function of both N intake and %CP, and the partitioning of total N excretion into urine as a function of %CP. There was less agreement between predictions and observations for feces N excretion as a function of %CP (r(2) = 0.003 to 0.14) than N intake (r(2) = 0.52 to 0.75), indicating that %CP is not a good predictor of fecal N excretion. The empirical equations provide a simple tool that, if used with caution, could predict N excretion characteristics for a wide range of dietary and animal characteristics and could improve ammonia emissions estimates by process-based models.

Nitrous oxide (N₂O) emissions from concentrated animal feeding operations, including cattle feedyards, have become an important research topic. However, there are limitations to current measurement techniques, uncertainty in the magnitude of feedyard N₂O fluxes, and a lack of effective mitigation methods. The objective of this review was to assess N₂O emission from cattle feedyards, including comparison of measured and modeled emission rates, discussion of measurement methods, and evaluation of mitigation options. Published annual per capita flux rates for beef cattle feedyards and open‐lot dairies were highly variable and ranged from 0.002 to 4.3 kg N₂O animal⁻¹ yr⁻¹. On an area basis, published emission rates ranged from 0 to 41 mg N₂O m⁻² h⁻¹. From these studies and Intergovernmental Panel on Climate Change emission factors, calculated daily per capita N₂O fluxes averaged 18 ± 10 g N₂O animal⁻¹ d⁻¹ (range, 0.04–67 g N₂O animal⁻¹ d⁻¹). This variation was due to inconsistency in measurement techniques as well as irregularity in N₂O production and emission attributable to management, animal diet, and environmental conditions. Based on this review, it is clear that the magnitude and dynamics of N₂O emissions from open‐lot cattle systems are not well understood. Further research is required to quantify feedyard N₂O fluxes and develop cost‐effective mitigation methods.Core Ideas: The magnitude of published N₂O fluxes from open‐lot cattle systems was highly variable. N2O fluxes varied with measurement methods, management, and environmental conditions. Methods to mitigate feedyard N2O emissions are available but have yet to be thoroughly evaluated. Improved animal performance and reducing N intake are best options to reduce feedyard N2O losses.

Organic dairy (OD) production is increasing in the Northeastern United States due to consumer demand. Some physicochemical properties of OD manure differ from conventional dairy (CD) manure, which could influence nutrient cycling and soil fertility differently when OD manure is applied as fertilizer to meet plant N demands. Effects of OD manure on activities of acid phosphomonoesterase (ACP), alkaline phosphomonoesterase (ALP), phosphodiesterase (PDE), available soil phosphorus (P), and plant growth were investigated in a greenhouse study, where sorghum-sudangrass (Sorghum bicolor subsp. drummondii) was fertilized with manures from 13 organic dairies in Maine, CD manure, or NH₄NO₃. Soil phosphatase activities and modified Morgan P were determined at planting and after 16 weeks of plant growth. Plant growth did not differ (P > 0.05) when fertilized with OD and CD manures or inorganic fertilizer. However, there was a wide range in growth with OD manure, which was negatively correlated to manure C:N and C:P (P < 0.05) ratios. After 16 weeks, OD manure amended soils had higher modified Morgan P than soils with inorganic fertilizer (P < 0.05), but there was no difference between OD and CD manured soils (P > 0.05). Of the three soil phosphatases, ACP activity was highest and increased with OD manure similarly to CD manure. There was a negative correlation (P < 0.01) between ACP activity and manure C:P ratio, suggesting that manure C content influences P cycling and may reduce P availability in soils amended with OD manure, in a manner similar to CD manure.

The objectives of this study were to (1) examine the effects of plant condensed (CT) and hydrolyzable tannin (HT) extracts on CH₄ and N₂O emissions; (2) identify the reactions responsible for manure-derived GHG emissions, and (3) examine accompanying microbial community changes in fresh dairy manure. Five treatments were applied in triplicate to the freshly collected dairy manure, including 4% CT, 8% CT, 4% HT, 8% HT (V/V), and control (no tannin addition). Fresh dairy manure was placed into 710 mL glass incubation chambers. In vitro composted dairy manure samples were collected at 0, 24, 48, and 336 h after the start of incubation. Fluxes of N₂O and CH₄ were measured for 5-min/h for 14 d at a constant ambient incubation temperature of 39 °C. The addition of quebracho CT significantly decreased the CH₄ flux rates compared to the tannin-free controls (215.9 mg/m²/h), with peaks of 75.6 and 89.6 mg/m²/h for 4 and 8% CT inclusion rates, respectively. Furthermore, CT significantly reduced cumulative CH₄ emission by 68.2 and 57.3% at 4 and 8% CT addition, respectively. The HT treatments failed to affect CH₄ reduction. However, both CT and HT reduced (p < 0.001) cumulative and flux rates of N₂O emissions. The decrease in CH₄ flux with CT was associated with a reduction in the abundance of Bacteroidetes and Proteobacteria.