Impacts of feedlot floor condition, deposition frequency, and inhibitors on N2O and CH4 emissions from feedlot dung and urine patches

Impacts of slurry application methods and inhibitors on gaseous emissions and N2O pathways in meadow-cinnamon soil

This study aimed to evaluate the impact of mitigation practices (slurry application methods and inhibitors applications) on gas emissions and identify the soil N₂O production pathways in cattle slurry applied soil using isotopocule mapping approach. First, we compared the NH₃ and N₂O emissions of cattle slurry applied soil in a summer maize field experiment in north China plain (NCP) with four treatments: control (CK, no fertilization), slurry application using surface (SA-S), slurry application using band application (BA-S), and chemical fertilizer application using band application (BA-C). Then, an incubation experiment was conducted to investigate the mitigation effect of nitrification inhibitors (dicyandiamide, DCD) and denitrification inhibitors (procyanidins, PC) and their combination (DCD + PC) on gaseous N emissions with slurry applied using incorporation (IA) or surface application (SA) methods. The results showed that the total gaseous N emissions (N₂O-N and NH₃-N) in field were in the order of SA-S (1534 mg m^-2) > BA-S (338 mg m^-2) > BA-C (128 mg m^-2) > CK (55 mg m^-2), and the dominant N loss contributor varied from NH₃ in SA-S (∼89%) to N₂O in BA-S (∼94%) and BA-C (∼88%). Moreover, the isotopocule mapping approach indicated that emitted N₂O of the slurry applied soil in field appeared to have lower r_N2O values and led to more N₂O + N₂ emissions at the initial fertilization period. The incubation experiment indicated that the N₂O emissions of slurry-applied soil were significantly reduced by DCD (∼45%) and DCD + PC (∼67%) application in comparison with CK (p < 0.05), and the stronger contributions of bacterial denitrification/nitrifier denitrification to N₂O production were revealed by the lower δ¹⁵N^SP in N₂O using the isotopocule mapping approach. In conclusion, in NCP the gaseous losses of the slurry applied field can be largely reduced by using incorporation method, and greater reduction could be achieved given the simultaneous application of nitrification/denitrification inhibitors.

Effects of rumen undegradable protein sources on nitrous oxide, methane and ammonia emission from the manure of feedlot-finished cattle

The effects of sources of rumen undegradable protein (RUP) in diets on methane (CH₄), nitrous oxide (N₂O) and ammonia (NH₃) emissions from the manure of feedlot-finished cattle were evaluated. We hypothesized that the use of different RUP sources in diets would reduce N loss via urine and contribute to reduced N₂O, CH₄ and NH₃ emissions to the environment. Nellore cattle received different diets (18 animals/treatment), including soybean meal (SM, RDP source), by-pass soybean meal (BSM, RUP source) and corn gluten meal (CGM, RUP source). The protein source did not affect the N and C concentration in urine, C concentration in feces, and N balance (P > 0.05). The RUP sources resulted in a higher N₂O emission than the RDP source (P = 0.030), while BSM resulted in a higher N₂O emission than CGM (P = 0.038) (SM = 633, BSM = 2521, and CGM = 1153 g ha⁻² N–N₂O); however, there were no differences in CH₄ and NH₃ emission (P > 0.05). In conclusion, the use of RUP in diets did not affect N excretion of beef cattle or CH₄ and NH₃ emission from manure, but increased N₂O emission from the manure.

Nitrous Oxide from Beef Cattle Manure: Effects of Temperature, Water Addition and Manure Properties on Denitrification and Nitrification

Beef feedyards produce nitrous oxide (N2O), a potent greenhouse gas. Limited research has evaluated the processes that produce feedyard N2O, and how rainfall and temperature impact N2O losses. Manure in feedyard pens develops into a complex ecosystem of microbes, extracellular enzymes, feces, and urine, with varying H2O content. This study aimed to improve understanding of feedyard N cycling under differing environmental conditions by incubation of manure in simulated feedyard pens using large chambers under laboratory conditions. We hypothesized that nitrification was the primary source of feedyard N2O, with interactions among temperature, H2O content, and manure properties. Emissions of N2O were monitored with a real–time N2O analyzer. Manure samples were taken at intervals for analyses of physicochemical properties, denitrification enzyme activity (DEA), and nitrification activity (NA). Due to equipment limitations, there was only one chamber per temperature tested. Correlation was poor among N2O emissions and rates of DEA and NA. However, significant relationships were found among key manure characteristics, such as ammonia/ammonium and nitrate/nitrite concentrations, manure dry matter, redox status, and temperature. These data suggest that most N2O was derived from denitrification in the top 5 cm of the manure pack. Further study is warranted to identify the processes involved in flushes of N2O emitted immediately after rainfall, possibly due to abiotic chemical reactions that release N2O sequestered in manure pores.

Trade-offs of gaseous emissions from soils under vegetable, wheat-maize and apple orchard cropping systems applied with digestate: An incubation study

Land application of digestate from anaerobic digestion causes various gaseous emissions. A soil core incubation experiment was carried out in the laboratory to investigate the trade-offs of NH₃, N₂O and CH₄ emissions from soils collected from vegetable, arable and orchard cropping systems. Digestate derived from liquid cattle manure was applied to the soil cores through the surface (SA) and incorporation application (IA) methods under three soil moisture conditions (40%, 60%, and 80% water-filled pore space, WFPS). Gaseous emissions from vegetable soil were significantly greater (P< .05) than those from soils under the other two cropping systems under similar conditions, particularly under a high moisture condition. The greenhouse gas emissions (GHG, in term of CO₂-equivalents) of all soils increased with the increasing soil moisture contents, mainly due to rapidly increasing N₂O emissions. Trade-offs in the emissions of these three gases were observed between SA and IA. As expected, SA was characterized by greater NH₃ and CH₄ but lower N₂O emissions compared to IA. The increase in GHG under IA could be offset only somewhat by the reduced NH₃ (and this reduced indirect N₂O) and CH₄ emissions under lower moisture conditions (<60% WFPS), which indicates a requirement for other strategies to control gaseous emissions from wet soils applied with digestate. In conclusion, an environmentally friendly strategy for digestate application should consider the soil moisture, types of soils and application methods, and all the presented suggestions need to be verified in the field in the future.Implications: This study shows that digestate incorporation can decrease NH3 but increase GHG emissions verse the surface application method, where the increased GHG could only be offset by the NH3 reductions at relatively dry soil condition, indicating an urgent requirement to mitigating GHG emissions under moist soil condition.