The effects of different cow urinary nitrogen rates on gaseous nitrogen fluxes from pasture soil

Cattle grazing pasture deposit urine at high nitrogen (N) rates that can impact the environment. Among the loss pathways, denitrification, which produces nitrous oxide (N2O) and dinitrogen (N2), is a major way that N can be lost to the atmosphere. There is limited information about N2 losses from grazed-pasture systems after urine deposition due to the method limitations with high ambient N2 concentrations. In this study, the 15N flux method and a high sampling frequency were used to explore N2 and N2O fluxes over time after urine application at two rates (400 and 800 kg N ha-1) on a New Zealand grazed pasture soil. N2O fluxes were significantly higher from the higher N application rate compared with the lower rate but there was no significant difference in N2 fluxes. Dinitrogen was the predominant gaseous N form lost from the applied urinary-N, contributing 32.1 ± 4.1% and 14.4 ± 1.7% of the total deposited N from 400 kg N ha-1 and 800 kg N ha-1, respectively, over the 95 measurement days. Denitrification and codenitrification both occurred in the pasture system, with denitrification being the predominant N2 production pathway, contributing 97.9 – 98.5% of the total N2 production. The similar N2 losses between the two urine-N rates is speculated to be due to enhanced ammonia volatilisation and transfer of N as nitrate, to deeper soil layers at the higher N rate. Soil relative gas diffusivity indicated that high N2 fluxes may have resulted from entrapped N2 diffusing from the draining soil

Temporal in situ synmics of N20 reductase activity as affected by nitrogen fertilization and implications for the N20/(N20+N2) product ratio and N20 mitigation.

In vitro, high nitrate (NO3) concentrations significantly inhibit N2O reductase activity. However, little information is available on the in situ temporal effects of excessive N fertilization on soil N2O reductase activity and the regulation of the N2O/(N2 + N2O) product ratio in agricultural soil. This study examined the monthly in situ dynamics of NO3 − concentration, N2O reductase activity, and N2O/(N2 + N2O) product ratio for 2 years in loamy soil that had received either continuous N fertilizer at 400 kg N ha−1 year−1 for 15 years (N400) or no N fertilizers (CK). N2O reductase activity was significantly lower under the N400 treatment than under the CK and correlated negatively with soil NO3 − concentration. The decrease in N2O reductase activity resulted in the N2O/(N2 + N2O) product ratio increasing. These results demonstrate that excessive N fertilization has the potential to increase N2O emissions by reducing N2O reductase activity in soils. These results highlight the need for N2O mitigation options to embrace the reduction of soil NO3 − concentrations

In situ nitrous oxide and dinitrogen fluxes from a grazed pasture soil following cow urine application at two nitrogen rates

Cattle grazing of pastures deposits urine onto the pasture soil at high nitrogen (N) rates that exceed the pasture's immediate N demands, increasing the risk of N loss. Nitrous oxide (N2O), a greenhouse gas, and dinitrogen (N2) are lost from the cattle urine patches. There is limited information on the in situ loss of N2 from grazed-pasture systems which is needed for understanding pasture soil N dynamics and balances. The 15N flux method was used to determine N2 and N2O fluxes over time following synthetic urine-15N application at either 400 or 800 kg N ha−1 to a grazed perennial pasture soil. Results showed that daily N2O fluxes were higher under 800 kg N ha−1 than under 400 kg N ha−1, but there was no significant difference in N2 fluxes. Cumulative N2O emissions from soil with 400 kg N ha−1 and 800 kg N ha−1 applied represented 0.16 ± 0.08% and 0.43 ± 0.08% of deposited N, respectively, while emitted N2 accounted for 32.1 ± 4.1% and 14.4 ± 1.7%, respectively, over 95 days after urine application. Codenitrification and denitrification co-occurred, with denitrification accounting for 97.9 to 98.5% of total N2 production. Recovery of urine-15N in pasture decreased with increasing N rate with 14.7 ± 0.5% and 9.9 ± 0.8% recovered at 400 and 800 kg N ha−1, respectively after 95 days. The N2O/(N2 + N2O) product ratio was generally higher during periods of nitrification of urine-N (the first month after urine application) but with no clear relationship to other measured variables. Contrary to our hypothesis, an elevated urine-N rate did not enhance N2 loss. This is speculated to be due to enhanced ammonia volatilisation and transfer of N as nitrate, to deeper soil layers. Soil relative gas diffusivity indicated that high N2 fluxes resulted from entrapped N2 diffusing from the draining soil

Nitrous oxide and dinitrogen fluxes from grazed pasture soil after cattle urine deposition

Ruminant cattle grazing pasture result in urine deposition at high nitrogen (N) rates that can impact the environment including via gaseous emissions. Among those lost pathways, nitrogen gas emission, especially nitrous oxide (N₂O) and dinitrogen (N2), is the primary way where N can be lost to the atmosphere. There is limited information on the magnitude or fluxes of N2 losses from grazed-pasture systems after urine deposition due to the method limitation. We used the 15N flux method and high sampling frequency to explore N2 and N₂O fluxes over time after urine application at two rates (400 and 800 kg N ha-1) on a New Zealand grazed pasture soil. The higher N rate significantly increased daily N₂O fluxes but has no significant effect on daily N2 fluxes in our study compared with the lower rate. N2 is the predominant gaseous N form lost from the applied urinary-N which contributed 32.1 ± 4.1% and 14.4 ± 1.7% of the total deposited-N from 400 kg N ha-1 and 800 kg N ha-1 respectively, over 95 measurement days. Denitrification and codenitrification co-occurred in the pasture system, with denitrification being the predominant N2 production pathway, contributing 97.9 – 98.5 % of total N2 production. The N₂O/(N2+N₂O) product ratio was generally higher during periods of nitrification (the first month after urine application) but with no clear relationship to other measured variables. Contrary to our hypothesis, an elevated urine-N rate did not enhance N2 loss. This is speculated to be due to enhanced ammonia volatilisation and transfer of N as nitrate, to deeper soil layers. Soil relative gas diffusivity indicated that high N2 fluxes resulted from entrapped N2 diffusing from the draining soil