Nitrous oxide emissions from an irrigated soil as affected by fertilizer and straw management

Nitrous oxide (N₂O) emission from farmland is a concern for both environmental quality and agricultural productivity. Field experiments were conducted in 1996–1997 to assess soil N₂O emissions as affected by timing of N fertilizer application and straw/tillage practices for crop production under irrigation in southern Alberta. The crops were soft wheat (Triticum aestivumL.) in 1996 and canola (Brassica napusL.) in 1997. Nitrous oxide flux from soil was measured using a vented chamber technique and calculated from the increase in concentration with time. Nitrous oxide fluxes for all treatments varied greatly during the year, with the greatest fluxes occurring in association with freeze-thaw events during March and April. Emissions were greater when N fertilizer (100 kg N ha⁻¹) was applied in the fall compared to spring application. Straw removal at harvest in the fall increased N₂O emissions when N fertilizer was applied in the fall, but decreased emissions when no fertilizer was applied. Fall plowing also increased N₂O emissions compared to spring plowing or direct seeding. The study showed that N₂O emissions may be minimized by applying N fertilizer in spring, retaining straw, and incorporating it in spring. The estimates of regional N₂O emissions based on a fixed proportion of applied N may be tenuous since N₂O emission varied widely depending on straw and fertilizer management practices. This revised version was published online in August 2006 with corrections to the Cover Date.     

Influence of time and method of alfalfa stand termination on yield,seed quality,N uptake,soil properties and greenhouse gas emissions under different N fertility regimes

A field experiment was conducted in a 7-year old alfalfa stand to compare the influence of time and method of terminating alfalfa stands on crop yield, seed quality, N uptake and recovery of applied N for wheat (Triticum aestivum L.) and canola (Brassica napus L.), soil properties (ammonium-N, nitrate-N, bulk density, total and light fraction organic C and N), and N₂O emissions on a Gray Luvisol (Typic Cryoboralf) loam near Star City, Saskatchewan, Canada. The treatments were a 3 × 3 × 4 factorial combination of three termination methods [herbicide (H), tillage (T), and herbicide + tillage (HT)], three termination times (after cut 1 and cut 2 in 2003, and in spring 2004) and four rates of N (0, 40, 80 and 120 kg N ha⁻¹) applied at seeding to wheat-canola rotation from 2004 to 2007. In the termination year, soil nitrate-N was considerably higher in T or HT treatments than in the H treatment and decreased with delay in termination. In the first crop year, seed and straw yields of wheat grown on T and HT treatments were significantly greater than H alone (by 1,055–1,071 kg seed ha⁻¹ and by 869–929 kg straw ha⁻¹), due to greater content of soil available N in T treatments. Yields decreased with delay in termination time. In general, yield and N uptake in seed and straw, and protein concentration tended to increase with increasing N rate. A greater yield increase occurred on the H compared to T and HT treatments from the first increments of N applied. Nitrous oxide emissions were generally low and there were no treatment differences evident when cumulative 4-year N₂O-N losses were compared. Appropriate N fertilization was able to compensate for yield reductions due to delayed termination timing, but could not do so entirely for yield reductions on the H compared to T or HT termination method. The amounts of TOC, TON, LFOC and LFON after four growing seasons were usually higher or tended to be higher under H treatment than under T treatment in the 0–5 cm soil layer, but the opposite was true in the 5–10 cm or 10–15 cm soil layers.     

Nitrous Oxide Emissions from a Fertilized and Grazed Grassland in the South East of Ireland

Agriculture currently accounts for 28% of national greenhouse gas emissions in Ireland. Nitrous oxide (N₂O) emissions from agricultural soils account for 38% of this total. A 2-year study was conducted, using the chamber technique on a fertilized and grazed grassland to quantify the effect of fertilizer application rate, soil and meteorological variables on N₂O emissions. Three N fertilizer regimes (0, 225 & 390 kg N ha⁻¹) were imposed with three replicates of each treatment. Nitrogen fertilizer was applied as urea (46% N) in spring with calcium ammonium nitrate (CAN-26% N) applied in the summer (June–September). Rotational grazing was practiced using steers. Nitrous oxide emissions arising from the unfertilized plots (0 N) were consistently low. Emissions from the N-fertilized plots (225 & 390 kg N ha⁻¹) were concentrated in relatively short periods (1–2 weeks) following fertilizer applications and grazing, with marked differences between treatments, relative patterns and magnitudes of emissions at different times of the year and between years. Variation in N₂O emissions throughout both years was pronounced with mean coefficients of variation of 116% in year 1 and 101% in year 2. The study encompassed two climatologically contrasting years. As a result the N₂O–N loss, as a percent of the N applied in the cooler and wetter 2002 (0.2–2.0%), were similar to those used for N-fertilized grasslands under the Intergovernmental Panel on Climate Change (IPCC) N₂O emission inventory calculation methodology (1.25% ± 1). In contrast, the percentage losses in the warmer and drier 2003 (3.5–7.2%) were substantially higher.     

Effect of controlled-release fertilizer on nitrous oxide emission from a winter wheat field

A 2-year field experiment was conducted to study effects of application rate of controlled-release fertilizer (CRF) and urea on N₂O emission from a wheat cropping system. Two kinds of N fertilizers, CRF and urea, and four application rates (0, 100, 200 and 270?kg?N?ha^?1) were used. Results indicate that the application of either urea or CRF, increased total N₂O emission during the wheat growing period linearly from 32 to 164?%, with increasing N rate (p?<?0.05), compared to the zero N control, and the increase was less significant in CRF than urea treatments. Compared with urea, CRF significantly reduced N₂O emission by 25?C56?% during the wheat growing period (p?<?0.05), and the effect was more significant when N rate was higher. Grain yield increased in a power pattern from 24 to 43?% in urea treatments and from 30 to 45?% in CRF treatments with increasing N rate (p?<?0.05). Specific N₂O emission (N₂O emission per unit of yield) increased linearly from 31 to 114?% in urea treatments (p?<?0.05), and from 2 to 50?% in CRF treatments (p?<?0.05), with increasing N rate. Compared with urea, CRF significantly inhibited specific N₂O emission (p?<?0.05), and the effect increased with increasing N rate. Peaks of N₂O emission did not occur immediately after fertilization, but did immediately after rainfall events. CRF released fertilizer-N slowly, prolonging nitrogen supply and reducing peaks of N₂O fluxes stimulated by rainfall. The application rate of CRF could be reduced by 26?C50?% lower than that of urea for mitigating N₂O emission without sacrificing grain yield. We would not risk any significant loss of wheat yield while achieving economic and environmental benefits by reducing urea or CRF application rate from 270?kg to 200?kg?N?ha^?1.     

Method and timing of grassland renovation affects herbage yield,nitrate leaching,and nitrous oxide emission in intensively managed grasslands

Managed grasslands are occasionally ploughed up and reseeded in order to maintain or increase the sward productivity. It has been reported that this renovation of grassland is associated with a flush of soil organic nitrogen (N) mineralization and with a temporary increase in soil mineral N contents. Here, we report on the effects of method and time of grassland renovation on herbage yield, nitrate (NO₃ ⁻) leaching and nitrous oxide (N₂O) emission. Field experiments were carried out at three sites (two sandy soils and a clay soil) in the Netherlands for three years. Renovation of grassland increased the percentage of Perennial ryegrass from 48–70% up to more than 90%. However, averaged over three years, dry matter yields were higher for the reference (not reseeded) swards (on average 13.6 Mg ha⁻¹ for the highest N application rate) than for the renovated grasslands (12.2–13.1 Mg ha⁻¹ dry matter). Grassland renovation in April did not increase N leaching in comparison to the reference. However, renovation in September increased the risk of leaching, because mineral N contents in the 0–90 cm were in November on average 46–77 kg N ha⁻¹ higher than in the reference. Contents of dissolved organic N (DON) in the soil were not affected by renovation. Renovation increased N₂O emissions by a factor of 1.8–3.0 relative to the reference grassland. Emissions of N₂O were on average higher after renovation in April (8.2 kg N₂O-N ha⁻¹) than in September (5.8 kg N₂O-N ha⁻¹). Renovation without ploughing (i.e. only chemically destruction of the sward) resulted in a lower percentage of perennial ryegrass (60–84%) than with ploughing (>90%). Moreover, N₂O emissions were higher after renovation without ploughing than with ploughing. Clearly, farmers need better recommendations and tools for determining when grassland renovation has beneficial agronomic effects. Losses of N via leaching and N₂O emission after renovation can probably not be avoided, but renovation in spring in stead of autumn in combination with ploughing and proper timing of fertilizer application can minimize N losses.     

Impact of different forms of N fertilizer on N2O emissions from intensive grassland

Nitrous oxide (N₂O) emissions were measured over two years from an intensively managed grassland site in the UK. Emissions from ammonium nitrate (AN) and urea (UR) were compared to those from urea modified by various inhibitors (a nitrification inhibitor, UR(N), a urease inhibitor, UR(U), and both inhibitors together, SU), as well as a controlled release urea (CR). N₂O fluxes varied through time and between treatments. The differences between the treatments were not consistent throughout the year. After the spring and early summer fertilizer applications, fluxes from AN plots were greater than fluxes from UR plots, e.g. the cumulative fluxes for one month after N application in June 1999 were 5.2 ± 1.1 kg N₂O-N ha^–1 from the AN plots, compared to 1.4 ± 1.0 kg N₂O-N ha^–1 from the UR plots. However, after the late summer application, there was no difference between the two treatments, e.g. cumulative fluxes for the month following N application in August 2000 were 3.3 ± 0.7 kg N₂O-N ha^–1 from the AN plots and 2.9 ± 1.1 kg N₂O-N ha^–1 from the UR plots. After all N applications, fluxes from the UR(N) plots were much less than those from either the AN or the UR plots, e.g. 0.2 ± 0.1 kg N₂O-N ha^–1 in June 1999 and 1.1 ± 0.3 kg N₂O-N ha^–1 in August 2000. Combining the results of this experiment with earlier work showed that there was a greater N₂O emission response to rainfall around the time of fertilizer application in the AN plots than in the UR plots. It was concluded that there is scope for reducing N₂O emissions from N-fertilized grassland by applying UR instead of AN to wet soils in cool conditions, e.g. when grass growth begins in spring. Applying UR with a nitrification inhibitor could cut emissions further.     

Effect of encapsulated calcium carbide and urea application methods on denitrification and N loss from flooded rice

Poor N fertilizer use efficiency by flooded rice is caused by gaseous losses of N. Improved fertilizer management and use of nitrification inhibitors may reduce N losses. A microplot study using¹⁵N-labelled urea was conducted to investigate the effects of fertilizer application method (urea broadcast, incorporated, deep-placed) and nitrification inhibitor [encapsulated calcium carbide (ECC)] treatments on emission of N₂+N₂0 and total loss of applied N on a grey clay near Griffith, NSW, Australia. Both incorporation and deep placement of urea decreased N₂+N₂O emission compared to urea broadcast into the floodwater. Addition of ECC significantly (P < 0.05) reduced emission of N₂+N₂0 from incorporated or deep-placed urea and resulted in increased exchangeable ammonium concentrations in the soil in both treatments. Fifty percent of the applied N was lost when urea was broadcast into the floodwater. Total N loss from the applied N was significantly (P < 0.05) reduced when urea was either incorporated or deep placed. In the presence of ECC the losses were reduced further and the lowest loss (34.2% of the applied N) was noted when urea was deep-placed with ECC.     

Fertilizer dynamics in different tillage and crop rotation systems in a Vertisol in Central Mexico

N-fertilization dynamics and agronomic practices on a Vertisol in central Mexico were evaluated under irrigated conditions: (1) wheat-maize rotation with conventional tillage (CT) and burning of residues (W-M/CT/B, regional control); (2) wheat-beans rotation with CT and incorporation of residues into the soil (W-P/CT/I); (3) wheat-maize rotation with CT and incorporation of residues into the soil (W-M/CT/I); (4) maize-beans rotation bi-annual with CT and incorporation of residues into the soil (M-P/CT/Bi); and (5) wheat-maize, no tillage (NT) and residues left on the soil surface as mulch (W-M/NT/S). ¹⁵N and acetylene inhibition techniques were used to estimate N fertilizer efficiency and losses (N₂ + N₂O). Treatments received 240, 60, and 300 kg N ha⁻¹ for spring maize, beans and winter wheat, as ammonium sulphate enriched with 5.468% atoms ¹⁵N excess. In the spring summer cycle, the fertilizer N recovery ranged from 27% for W-M/NT/S to 68% for M-P/CT/Bi. From the total N-fertilizer applied, only 3 to 9% remained in soil after harvest (W-M/NT/S and W-M/CT/I being the respective extremes). Unaccounted N-fertilizer ranged between 27 and 69%, the highest losses corresponding to W-M/NT/S treatment. Fertilizer N recovery in wheat varied from 19 to 37% (W-M/NT/S–W-M/CT/B). N-fertilizer remaining in soil was 14 to 24% (W-M/NT/S – W-M/CT/I). N₂ and N₂O emissions were higher in the no tillage system. Emissions ranged from 3 to 28 kg N ha⁻¹ for W-P/CT/I and W-M/NT/S, respectively. The best treatments were those in which residues were incorporated resulting in N immobilization in top soil (0–15 cm), small N gas losses, and higher soil organic matter, these treatments were W-P/CT/I, W-M/CT/I.     

Partial balance of nitrogen in a maize cropping system in humic nitisol of Central Kenya

The application of nitrogen in a soil under agricultural production is subject to several pathways including de-nitrification, leaching and recovery by an annual crop. This is as well greatly influenced by the management practices, nitrogen source and soil conditions. The main objective of this study was to investigate the loss of nitrogen (N) through nitrous oxide (N₂O) emissions and mineral N leaching and uptake by annual crop as influenced by the N source. The study was carried out at Kabete in Central Kenya. Measurements were taken during the second season after two seasons of repeated application of N as urea and Tithonia diversifolia (tithonia) leaves. Results obtained indicated that nitrous oxide (N₂O) emissions at 4 weeks after planting were as high as 12.3 μg N m ⁻² h⁻¹ for tithonia treatment and 2.9 μg N m⁻² h⁻¹ for urea treatment. Tithonia green biomass treatment was found to emit N₂O at relatively higher rate compared to urea treatment. This was only evident during the fourth week after treatment application.Soil mineral N content at the end of the season increased down the profile. This was evident in the three treatments (urea, tithonia and control) investigated in the study. Urea treatment exhibited significantly higher mineral N content down the soil profile (9% of the applied N) compared to tithonia (0.6% of the applied N). This was attributed to the washing down of the nitrate-N from the topsoil accumulating in the lower layers of the soil profile. However, there was no significant difference in N content down the soil profile between tithonia treatment and the control. It could be concluded that there was no nitrate leaching in the tithonia treatment. Nitrogen recovery by the maize crop was higher in the urea treatment (76% of the applied N) as compared to tithonia treatment (55.5% of the applied N). This was also true for the residual mineral N in the soil at the end of the season which was about 7.8% of the applied N in the urea treatment and 5.2% in the tithonia treatment.From this study, it was therefore evident that although there is relatively lower N recovery by maize supplied with tithonia green biomass compared to maize supplied with urea, more nitrogen is being lost (through leaching) from the soil–plant system in the urea applied plots than in tithonia applied plots. However, a greater percentage (37.8%) of the tithonia-applied N could not be accounted for and might have been entrapped in the soil organic matter unlike urea-applied N whose greater percentage (92%) could be accounted for.     

Effects of fertiliser type and the presence or absence of plants on nitrous oxide emissions from irrigated soils

Nitrous oxide (N₂O) emissions and denitrification losses from an irrigated sandy loam soil amended with composted municipal solid waste (MSW), sheep manure (SM), surface applied pig slurry (SPS), incorporated pig slurry (IPS) or urea (U) were studied under Mediterranean conditions. We quantified emissions, in both the presence and absence of maize and N₂O production, via denitrification and nitrification pathways using varying concentrations of acetylene. Discounting the N₂O lost in the Control, the percentages of N₂O lost in relation to the total N applied were greater for urea (1.80%) than for MSW (0.50%), SM (0.46%), SPS (1.02%) or IPS (1.27%). In general, plots treated with organic fertilisers emitted higher amounts of N₂O when under maize than bare soil plots. On the other hand, greater denitrification losses were also recorded for plots in the absence of plants (between 9.7 and 29.3 kg N₂O-N ha⁻¹) than for areas with plants (between 7.1 and 24.1 kg N₂O-N ha⁻¹). The proportion of N₂O produced via denitrification was greater from fertiliser treatments than for the controls and also greater without plants (between 66 and 91 % of the N₂O emitted) than with plants (between 48 and 81%).     

Effect of increased N use and dry periods on N<Subscript>2</Subscript>O emission from a fertilized grassland

To better understand the effects of increased N input and dry periods on soil nitrous oxide (N₂O) emission, we examined a unique data-set of weather, soil microclimate, N input, and N₂O emissions (using the eddy covariance method), measured at a fertilized grassland over the period 2003–2008. We found that the N₂O emission (11.5 kg N ha⁻¹ year⁻¹), the ratio of N₂O emission to N input (3.4), and the duration of elevated N₂O flux (57 days) in 2003 were about two times greater than those of the following years. 2003 had the highest annual N input (343 kg N ha⁻¹ year⁻¹) which exceeded the agronomical requirements for Irish grasslands (up to 306 kg ha⁻¹ year⁻¹). In the summer of 2003, the site had a significantly higher soil temperature, lower WFPS and lowest rainfall of all years. Large N₂O emission events followed rainfall after a long dry period in the summer of 2003, attributed to dominant nitrification processes. Furthermore, in the non summer periods, when temperature was lower and WFPS was higher and when there were prior N applications, lower N₂O emissions occurred and were attributed to dominant denitrification processes. Throughout the study period, the N input and soil dryness related factors (duration of WFPS under 50%, summer average WFPS, and low rainfall) showed exponential relationships with N₂O emission and the ratio of N₂O emission to N input. Based on these findings, we infer that the observed anomalously high N₂O emission in 2003 may have been caused by the combined effects of excess N input above the plant uptake rate, elevated soil temperature, and N₂O flux bursts that followed the rewetting of dry soil after an unusually long dry summer period. These results suggest that high N input above plant uptake rate and extended dry periods may cause abnormal increases in N₂O emissions.     

Temporal and Spatial Variations in N2O Emissions from a Chinese Cabbage Field as a Function of Type of Fertilizer and Application

We conducted a field experiment in an Andosol near Tsukuba (Japan) to study the effects of the type of nitrogen fertilizer on nitrous oxide (N₂O) emissions and on nitrogen uptake by Chinese cabbage (Brassica campestris L.). We used four treatments: fertilizer containing no nitrogen (CONT), broadcast application of urea (BR-U), band application of urea (B-U), and band application of controlled-release urea (B-CU). The application rate was 250 kg N ha⁻¹, a conventional rate in the region. We measured N₂O flux two or three times a week during the 82-day growth period, then divided the cumulative emissions into three stages: early (28 days), middle (27 days), and late (27 days). The temporal variation in N₂O emissions differed among the treatments. Broadcast urea application produced 70% of N₂O emissions during the early stage. N₂O emissions increased with increasing cabbage growth in the CONT treatment, indicating that plant growth accompanied by increasing root biomass could stimulate N₂O emissions from unfertilized soil. There were no differences in the patterns of temporal variation in N₂O flux between the two band applications (B-U and B-CU); N₂O emissions in the early and middle stages were 46 and 42%, respectively, for B-U, vs. 41 and 40% for B-CU. However, the overall N₂O emission was reduced by 40.5% in the B-CU treatment compared with the B-U treatment. N₂O emissions from the soils within fertilized bands were dramatically higher than those between the fertilized bands, and this trend continued until harvesting.     

Effects of N management on N2O and CH4 fluxes and15N

Forage production in irrigated mountain meadows plays a vital role in the livestock industry in Colorado and Wyoming. Mountain meadows are areas of intensive fertilization and irrigation which may impact regional CH₄ and N₂O fluxes. Nitrogen fertilization typically increases yields, but N-use efficiency is generally low. Neither the amount of fertilizer-N recovered by the forage nor the effect on N₂O and CH₄ emissions were known. These trace gases are long-lived in the atmosphere and contribute to global warming potential and stratospheric ozone depletion. From 1991 through 1993 studies were conducted to determine the effect of N source, and timing of N-fertilization on forage yield, N-uptake, and trace gas fluxes at the CSU Beef Improvement Center near Saratoga, Wyoming. Plots were fertilized with 168 kg N ha^-1. Microplots labeled with¹⁵N-fertilizer were established to trace the fate of the added N. Weekly fluxes of N₂O and CH₄ were measured during the snow-free periods of the year. Although CH₄ was consumed when soils were drying, flood irrigation converted the meadow into a net source of CH₄. Nitrogen fertilization did not affect CH₄ flux but increased N₂O emissions. About 5% of the applied N was lost as N₂O from spring applied NH₄NO₃, far greater than the amount lost as N₂O from urea or fall applied NH₄NO₃. Fertilizer N additions increased forage biomass to a maximum of 14.6 Mg ha^-1 with spring applied NH₄NO₃. Plant uptake of N-fertilizer was greater with spring applications (42%), than with fall applications (22%).     

N2O and NO emissions from a field of Chinese cabbage as influenced by band application of urea or controlled-release urea fertilizers

A field experiment was conducted in an Andosol in Tsukuba, Japan to study the effect of banded fertilizer applications or reduced rate of fertilizer N (20% less) on emissions of nitrous oxide (N₂O) and nitric oxide (NO), and also crop yields of Chinese cabbage during the growing season in 2000. Six treatments were applied by randomized design with three replications, which were; no N fertilizer (CK); broadcast application of urea (BC); band application of urea (B); band application of urea at a rate 20% lower than B (BL); band application of controlled-release urea (CB) and band application of controlled-release urea at a rate 20% lower than CB (CBL). The results showed that reduced application rates, applied in bands, of both urea (BL) and controlled-release urea fertilizer (CBL) produced yields that were not significantly lower than yields from the full rate of broadcast urea (BC). The emissions of N₂O and NO from the reduced fertilizer treatments (BL, CBL) were lower than that of normal fertilizer rates (B, CB). N₂O and NO emissions from controlled-release urea applied in band mode (CB, CBL) were less than those from urea applied in band mode (B, BL). The total emissions of N₂O and NO indicated that applying fertilizers in band mode mitigated NO emission from soils, but N₂O emissions from banded urea (B) were no lower than from broadcast urea (BC).     

Reducing nitrous oxide emissions and optimizing nitrogen-use efficiency in dryland crop rotations with different nitrogen rates

Recent interests in improving agricultural production while minimizing environmental footprints emphasized the need for research on management strategies that reduce nitrous oxide (N₂O) emissions and increase nitrogen-use efficiency (NUE) of cropping systems. This study aimed to evaluate N₂O emissions, annualized crop grain yield, emission factor, and yield-scaled- and NUE-scaled N₂O emissions under continuous spring wheat (Triticum aestivum L.) (CW) and spring wheat–pea (Pisum sativum L.) (WP) rotations with four N fertilization rates (0, 50, 100, and 150 kg N ha^?1). The N₂O fluxes peaked immediately after N fertilization, intense precipitation, and snowmelt, which accounted for 75–85% of the total annual flux. Cumulative N₂O flux usually increased with increased N fertilization rate in all crop rotations and years. Annualized crop yield and NUE were greater in WP than CW for 0 kg N ha^?1 in all years, but the trend reversed with 100 kg N ha^?1 in 2013 and 2015. Crop yield maximized at 100 kg N ha^?1, but NUE declined linearly with increased N fertilization rate in all crop rotations and years. As N fertilization rate increased, N fertilizer-scaled N₂O flux decreased, but NUE-scaled N₂O flux increased non-linearly in all years, regardless of crop rotations. The yield-scaled N₂O flux decreased from 0 to 50 kg N ha^?1 and then increased with increased N fertilization rate. Because of non-significant difference of N₂O fluxes between 50 and 100 kg N ha^?1, but increased crop yield, N₂O emissions can be minimized while dryland crop yields and NUE can be optimized with 100 kg N ha^?1, regardless of crop rotations.

     

Emissions of N<Subscript>2</Subscript>O from fertilized and grazed grassland on organic soil in relation to groundwater level

Intensively managed grasslands on organic soils are a major source of nitrous oxide (N₂O) emissions. The Intergovernmental Panel on Climate Change (IPCC) therefore has set the default emission factor at 8 kg N–N₂O ha⁻¹ year⁻¹ for cultivation and management of organic soils. Also, the Dutch national reporting methodology for greenhouse gases uses a relatively high calculated emission factor of 4.7 kg N–N₂O ha⁻¹ year⁻¹. In addition to cultivation, the IPCC methodology and the Dutch national methodology account for N₂O emissions from N inputs through fertilizer applications and animal urine and faeces deposition to estimate annual N₂O emissions from cultivated and managed organic soils. However, neither approach accounts for other soil parameters that might control N₂O emissions such as groundwater level. In this paper we report on the relations between N₂O emissions, N inputs and groundwater level dynamics for a fertilized and grazed grassland on drained peat soil. We measured N₂O emissions from fields with different target groundwater levels of 40 cm (‘wet’) and 55 cm (‘dry’) below soil surface in the years 1992, 1993, 2002, 2006 and 2007. Average emissions equalled 29.5 kg N₂O–N ha⁻¹ year⁻¹ and 11.6 kg N–N₂O ha⁻¹ year⁻¹ for the dry and wet conditions, respectively. Especially under dry conditions, measured N₂O emissions exceeded current official estimates using the IPCC methodology and the Dutch national reporting methodology. The N₂O–N emissions equalled 8.2 and 3.2% of the total N inputs through fertilizers, manure and cattle droppings for the dry and wet field, respectively and were strongly related to average groundwater level (R ² = 0.74). We argue that this relation should be explored for other sites and could be used to derive accurate emission data for fertilized and grazed grasslands on organic soils.     

Nitrous oxide emissions from fertilized and unfertilized grasslands on peat soil

Emissions of nitrous oxide (N₂O) from managed and grazed grasslands on peat soils are amongst the highest emissions in the world per unit of surface of agriculturally managed soil. According to the IPCC methodology, the direct N₂O emissions from managed organic soils is the sum of N₂O emissions derived from N input, including fertilizers, urine and dung of grazing cattle, and a constant ‘background’ N₂O emission from decomposition of organic matter that depends on agro-climatic zone. In this paper we questioned the constant nature of this background emission from peat soils by monitoring N₂O emissions, groundwater levels, N inputs and soil NO₃ ⁻–N contents from 4 grazed and fertilized grassland fields on managed organic peat soil. Two fields had a relatively low groundwater level (‘dry’ fields) and two fields had a relatively high groundwater level (‘wet’ fields). To measure the background N₂O emission, unfertilized sub-plots were installed in each field. Measurements were performed monthly and after selected management events for 2 years (2008–2009). On the managed fields average cumulative emission equaled 21 ± 2 kg N ha⁻¹y⁻¹ for the ‘dry’ fields and 14 ± 3 kg N ha⁻¹y⁻¹ for the ‘wet’ fields. On the unfertilized sub-plots emissions equaled 4 ± 0.6 kg N ha⁻¹y⁻¹ for the ‘dry’ fields and 1 ± 0.7 kg N ha⁻¹y⁻¹ for the ‘wet’ fields, which is below the currently used estimates. Background emissions were closely correlated with groundwater level (R ² = 0.73) and accounted for approximately 22% of the cumulative N₂O emission for the dry fields and for approximately 10% of the cumulative N₂O emissions from the wet fields. The results of this study demonstrate that the accuracy of estimating direct N₂O emissions from peat soils can be improved by approximately 20% by applying a background emission of N₂O that depends on annual average groundwater level rather than applying a constant value.     

Use of urease inhibitors and urea fertilizers on winter wheat

Phosphoroamide urease inhibitors were evaluated for their ability to increase grain protein and yield of winter wheat (Triticum aestivum L.) when added to surfaceapplied urea-based fertilizers. Six urease inhibitors [trichloroethyl phosphorodiamidate, diethyl phosphoric triamide, dimethyl phosphoric triamide, N-(diaminophosphinyl)-cyclohexylamine, N-benzyl-N-methyl phosphoric triamide, and phenylphosphorodiamide] were evaluated. Nitrogen treatments were urea prills, urea solution, and ureaammonium nitrate (UAN) solution broadcast and UAN solution band applied. Ammonium sulfate and no N treatments were included as controls. Fertilizer treatments were applied in the fall and spring. Soils were Ryker silt loam (Typic Paleudalf), Rensselaer loam (Typic Argiaquoll), and Avonburg silt loam (Aeric Fragiaqualf).Grain yield was a more responsive indicator of N addition than was grain N content. Urea prills and ammonium sulfate were more effective fertilizers than was UAN solution. UAN was not more effective applied in a band than broadcast. Urease inhibitors did not improve the efficiency of urea fertilizers since NH₃ volatilization did not appear to be a problem following addition of urea fertilizers in spring or fall.Journal Paper No. 10528. This work was supported in part by a grant from Allied Chemical, Solvay, NY 13209.     

Nitrous oxide emissions from a light-textured arable soil of North-Western Russia: effects of crops,fertilizers, manures and climate parameters

Direct nitrous oxide emissions from a light-textured arable soil typical of North-Western Russia and subject to different management systems were measured during three growing seasons (May–September) in 2003–2005. Cumulative fluxes varied between 0.26 ± 0.06 and 2.98 ± 1.56 kg N₂O–N ha⁻¹, with the lowest flux produced where no N was added as mineral fertilizers/manures or where green manure/low inputs of mineral fertilizer were used as a source of N. Highest cumulative fluxes were measured from the plots where high inputs of farmyard manure were used. Of the crops studied, potatoes produced the highest N₂O fluxes; this was attributed to the use of furrows, in which the soil tended to be more compact with higher water-filled pore space, making the soil more prone to denitrification than that in fields without furrows. The available N content of the soil at the start of each growing season was quite low and cumulative N₂O fluxes were significantly affected by N-fertilizer application within one growing season. However, for different growing seasons with highly changeable rainfall patterns and with different soil management for different crops, the quite high yearly correlation between N application and N₂O fluxes was much reduced.     

Soil nitrogen response to coupling cover crops with manure injection

Coupling winter small grain cover crops (CC) with manure (M) application may increase retention of manure nitrogen (N) in corn (Zea mays L.), -soybean [Glycine max (L.) Merr], cropping systems. The objective of this research was to quantify soil N changes after application of liquid swine M (Sus scrofa L.) at target N rates of 112, 224, and 336 kg N ha⁻¹ with and without a CC. A winter rye (Secale cereale L.)-oat (Avena sativa L.) CC was established prior to fall M injection. Surface soil (0–20 cm) inorganic N concentrations were quantified every week for up to 6 weeks after M application in 2005 and 2006. Soil profile (0–120 cm in 5, 20-cm depth increments) inorganic N, total N, total organic carbon and bulk density were quantified for each depth increment in the fall before M application and before the CC was killed the following spring. Surface soil inorganic N on the day of application averaged 318 \textmg  \textN  \textkg ^{- 1}_\textsoil 318\,{\text{mg}}\;{\text{N}}\;{\text{kg}}^{ - 1}{_{\text{soil}}} in 2005 and 186 \textmg  \textN  \textkg ^{- 1}_\textsoil 186\,{\text{mg}}\;{\text{N}}\;{\text{kg}}^{ - 1}{_{\text{soil}} } in 2006 and stabilized at 150 \textmg  \textN  \textkg ^{- 1}_\textsoil 150\,{\text{mg}}\;{\text{N}}\;{\text{kg}}^{ - 1}{_{\text{soil}}} in both years by mid-November. Surface soil NO₃-N concentrations in the M band were more than 30 times higher in the fall of 2005 than in 2006. The CC reduced surface soil NO₃-N concentrations after manure application by 32% and 67% in mid- November 2005 and 2006, respectively. Manure applied at 224 kg N ha⁻¹ without a CC had significantly more soil profile inorganic-N (480 kg N ha⁻¹) in the spring after M application than manured soils with a CC for the 112 (298 kg N ha⁻¹) and 224 (281 kg N ha⁻¹) N rates, and equivalent inorganic N to the 336 (433 kg N ha⁻¹) N rate. These results quantify the potential for cover crops to enhance manure N retention and reduce N leaching potential in farming systems utilizing manure.