A low efficiency of use of N fertilisers has been observed in mid-Wales on permanent pasture grazed intensively by cattle. Earlier laboratories studies have suggested that heterogeneity in redox conditions at shallow soil depths may allow nitrification and denitrification to occur concurrently resulting in gaseous losses of N from both NH4+ and NO3–. The objective of the investigation was to test the hypothesis that both nitrification and denitrification can occur simultaneously under simulated field capacity conditions (∼5 kPa matric potential). Intact soil cores were taken from grassland subjected to both grazing and amenity use. The fate of applied NH4+ was examined during incubation. 15N was used as a tracer. Nitrapyrin was used as a nitrification inhibitor and acetylene was used to block N2O reductase. More than 50% of N applied as NH4+ disappeared over a period of 42 days from the soil mineral-N pool. Some of this N was evolved as N2O. Accumulation of NO3––N in the surface 0–2.5 cm indicated active nitrification. Addition of nitrapyrin increased N recovery by 26% and inhibited both the accumulation of NO3–N and emission of N2O. When intact field cores were incubated after addition of 15N-urea, all of the N2O evolved was derived from added urea-N. It was concluded that nitrification and denitrification do occur simultaneously in the top 7.5 cm or so, of the silty clay loam grassland topsoils of mid-Wales at moisture contents typical of field capacity. The quantitative importance of these concurrent processes to N loss from grassland systems has not yet been assessed.

Estimation of simultaneous nitrification and denitrification in grassland soil associated with urea-N using 15N and nitrification inhibitor

The spatial heterogeneity of N 2 O flux at short distances (0.1-2 m) was characterized in relation to various soil physical and chemical properties and the location of incorporated crop residues in arable soils. Plots were prepared with uniform compaction (either zero or compacted by a laden two-wheel-drive tractor) in two field experiments, one under winter barley (Hordeum vulgare), the other under oil-seed rape (Brassica napus). Flux measurements were made of N 2 O using small chambers (7.3 cm diameter) placed at intervals of approximately 10 cm along a transect (c. 2 m long) across the direction of application of the treatments of compaction and residue incorporation. The flux of N 2 O and many other measurements showed large variation over short distances, particularly when fluxes were small. The spatial variation of the flux was not closely related to the soil properties. Correlations showed that cone resistance, air permeability and closeness to incorporated residues were as important as soil NO 3 , NH 4 and soluble C in determining flux of N 2 O from non-compacted soils. Most properties of compacted soils did not correlate with N 2 O flux. Correlation and multiple regression analysis failed to establish consistent relations between soil environmental variables and N 2 O flux, but principal component regression indicated that, overall, N 2 O flux increased with decreasing distance from straw residues and air permeability, and with increasing cone resistance and wet bulk density.

Short‐range spatial variation of nitrous oxide fluxes in relation to compaction and straw residues

Urine-treated soils have been implicated as an important source of gaseous N losses to the atmosphere. The goal of our research was to quantify NH3 and N2O emissions from urine under different simplified and controlled soil conditions and to relate these results to urinary-N transformation processes in soil. We studied the influence of soil texture (coarse vs. fine sand), moisture distribution with depth, air-filled pore space, and rate of air movement, which affected both soil drying processes and emission rates. Laboratory experiments were performed with synthetic urine in both aerobic and anaerobic conditions. Texture was the most important factor controlling NH3 volatilization and N2O emission factors in urine-treated sands. Generally, the finer the sand texture, the higher the input of denitrification to the total N2O emissions; however, the air-filled pore space threshold, below which denitrification became dominant, was greater in coarse sand. In addition, the evaporation rate of the urine water component was found to be an important parameter in total NH3 and N2O emissions. Ammonia volatilization occurred during the first day of the treatments, with volatilization rates closely related to evaporation rates in both sand textures. Finer sand texture caused reductions in the urine evaporation rate and therefore in NH3 volatilization rates. Urine evaporation increased air-filled pore space, thereby improving aeration conditions in the sand that contribute to nitrification dominance of N2O production. Moreover, evaporation of urine, enriched with dissolved N2O, increased total N2O emission. Results from these simplified experiments need confirmation under field soil conditions.

Nitrous Oxide and Ammonia Emissions from Urine-Treated Soils: Texture Effect

A low efficiency of use of N fertilisers has been observed in mid-Wales on permanent pasture grazed intensively by cattle. Earlier laboratories studies have suggested that heterogeneity in redox conditions at shallow soil depths may allow nitrification and deni- trification to occur concurrently resulting in gaseous losses of N from both NH4 c and NO3 . The objective of the investigation was to test the hypothesis that both nitrification and denitrification can occur simultaneous- ly under simulated field capacity conditions (F5 kPa matric potential). Intact soil cores were taken from grassland subjected to both grazing and amenity use. The fate of applied NH4 c was examined during incuba- tion. 15 N was used as a tracer. Nitrapyrin was used as a nitrification inhibitor and acetylene was used to block N2O reductase. More than 50% of N applied as NH4 c

http://rd.springer.com/content/pdf/10.1007%2Fs003740050621.pdf

Estimation of simultaneous nitrification and denitrification in grassland soil associated with urea-N using 15 N

/pdf/characterisation-of-natural-and-synthetic-nitrification-2ql72l9c94.pdf

Characterisation of natural and synthetic nitrification inhibitors and their potential use in tomato cultivation

Concurrent nitrification and denitrification in compacted grassland soil.

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Concurrent nitrification and denitrification in compacted grassland soil.